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  • 1.
    Amiel, Joshua Johnstone
    et al.
    University of Sydney, Australia.
    Lindström, Tom
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology. Linköping University, The Institute of Technology. University of Sydney, Australia.
    Shine, Richard
    University of Sydney, Australia.
    Egg incubation effects generate positive correlations between size, speed and learning ability in young lizards2014In: Animal Cognition, ISSN 1435-9448, E-ISSN 1435-9456, Vol. 17, no 2, 337-347 p.Article in journal (Refereed)
    Abstract [en]

    Previous studies have suggested that body size and locomotor performance are targets of Darwinian selection in reptiles. However, much of the variation in these traits may derive from phenotypically plastic responses to incubation temperature, rather than from underlying genetic variation. Intriguingly, incubation temperature may also influence cognitive traits such as learning ability. Therefore, we might expect correlations between a reptiles size, locomotor speed and learning ability either due to selection on all of these traits or due to environmental effects during egg incubation. In the present study, we incubated lizard eggs (Scincidae: Bassiana duperreyi) under hot and cold thermal regimes and then assessed differences in hatchling body size, running speed and learning ability. We measured learning ability using a Y-maze and a food reward. We found high correlations between size, speed and learning ability, using two different metrics to quantify learning (time to solution, and directness of route), and showed that environmental effects (incubation temperature) cause these correlations. If widespread, such correlations challenge any simple interpretation of fitness advantages due to body size or speed within a population; for example, survivors may be larger and faster than nonsurvivors because of differences in learning ability, not because of their size or speed.

  • 2.
    Berg, Sofia
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology. Linköping University, The Institute of Technology.
    Community Robustness Analysis: Theoretical Approaches to Identifying Keystone Structures in Ecological Communities2013Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Most of the world’s ecosystems suffer from stress caused by human activities such as habitat destruction, fragmentation, overexploitation of species and climate change. These factors affect the reproduction and/or survival of individual species as well as interactions between species in ecological communities. Forthcoming effects of this are altered abundances, direct species loss, and indirect cascading extinctions, with yet largely unknown consequences on community structure and functioning. Today, biodiversity loss is of global concern since human society and welfare depend upon resources and services provided by ecosystems. The importance of considering entire ecological communities as a target for conservation and management has been increasingly recognized due to the interdependencie  of species. Our ability to make predictions of the response of ecological communities to stress and biodiversity loss is in need of a deeper understanding of how structure and dynamical processes contributes to the functioning and stability of a community. In this thesis I use mathematical theory and dynamical models to study the response of community structure and resilience to a variety of disturbances affecting species and species interactions, ranging from small perturbations (Papers I-II) to large perturbations (species extinctions, Papers IIIIV).

    In Paper I we develop Community Sensitivity Analysis (CSA) as an analytical tool to study how a small permanent perturbation to the intrinsic growth rate, or mortality rate, of species is expected to affect i) the resilience (return rate) and ii) the structure (distribution of species equilibrium abundances) of an ecological community. Species interactions are described using Lotka-Volterra predator-prey dynamics. We apply CSA on the pelagic food webs of Lake Vättern and the Baltic Sea, respectively, and find that a change in the mortality rate of large-bodied species has a higher impact on community resilience and structure, compared to a perturbation to small-bodied species. However, analyzing the effect of a proportional change to the growth or mortality rate of species (elasticity analysis) shows that smallbodied species have proportionally larger effects on species equilibrium abundances, but not on resilience. CSA can also be used to study the effect of permanent (absolute or proportional) changes to inter- and intraspecific interaction strengths. For the two pelagic systems used in this study, CSA reveal that changes in the effect of a prey on its consumer tend to affect community structure and resilience significantly more than changes in the effect of a predator on its prey.

    In Paper II we assess the importance of rare species for the structure and resilience of ecological communities. First we show analytically, for a two species predator-prey system, that a change in the intrinsic growth rate of the rare species affect resilience more than a change in the growth rate of the common species. To test the generality of these results we next apply CSA on complex model food webs. In the analysis we distinguish between four trophic groups, each including only species with a similar trophic position, to separate the effect of abundance from the trophic position of species. Using mixed effect models we find support for our analytical predictions. More precisely, we find a strong negative relationship between the importance (sensitivity) of a species and its equilibrium abundance within all consumer groups and a weaker, but significant, relationship for producer species. The results from this study suggest that rare species can act as keystones through their effect on both community resilience and community structure, regardless of its trophic position.

    In Paper III we evaluate the risk of food web collapse caused by different trait-based extinction scenarios. In previous studies, groups of species, e.g. rare species, large-bodied species and top predators, have been identified to be relatively more prone to extinctions and other studies have found that extinctions of such species have comparably small effects on the remaining community. Using mathematical models of species dynamics we study the response of ecological communities to species removal (i.e. the proportion of species needed to be primarily removed to cause a 50% reduction in species richness, R50) when species are sequentially removed from the food web based on eight different traits. We show, contrary to some previous studies of sequential extinction simulations, that communities can be very vulnerable to realistic species loss. We furthermore find that the response of communities seems to depend on whether the extinction sequence follows a bottom-up or top-down direction, making it difficult to identify one particular extinction sequence as the most important/severe sequence.

    Finally, in Paper IV we aim to identify traits of species that can be used to identify keystone species, in terms of causing the highest proportion of secondary extinctions following their loss, in food webs with different degree of disassembly. Moreover, we analyze if the loss of a species that triggers a cascade of many secondary extinctions are the same species being identified as a keystones using Community Sensitivity Analysis. To answer these questions we randomly remove species from a set of 100 model communities. We analyze the relationship between the number of secondary extinctions following the randomly removed species and a range of species traits in communities where i) 75-100% of the initial number of species remain, ii) 50-75% of all species remain, iii) 25-50% of all species remain and iv) only 0-25% of all species remain. We find that the variation in secondary extinctions explained using species traits increases when the degree of food web disassembly and food web connectance are taken into account. The most important trait varies for different degrees of food web disassembly and also depends on whether basal species can go primarily extinct or not. However, due to correlation between most important traits, we conclude that the key status of different traits is rather robust against structural changes in the model food webs. Interestingly, food webs seem to be most sensitive to a random species loss after the loss of more than 25% of all initial species, suggesting that there is a threshold from which secondary extinctions increases. We also conclude that species being identified as keystones, based on the effect of their loss, are to some extent the same species being identified as having the largest effect on community structure and resilience, respectively, following a small perturbation.

    List of papers
    1. Using sensitivity analysis to identify keystone species and keystone links in size-based food webs
    Open this publication in new window or tab >>Using sensitivity analysis to identify keystone species and keystone links in size-based food webs
    2011 (English)In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 120, no 4, 510-519 p.Article in journal (Refereed) Published
    Abstract [en]

    Human-induced alterations in the birth and mortality rates of species and in the strength of interactions within and between species can lead to changes in the structure and resilience of ecological communities. Recent research points to the importance of considering the distribution of body sizes of species when exploring the response of communities to such perturbations. Here, we present a new size-based approach for assessing the sensitivity and elasticity of community structure (species equilibrium abundances) and resilience (rate of return to equilibrium) to changes in the intrinsic growth rate of species and in the strengths of species interactions. We apply this approach on two natural systems, the pelagic communities of the Baltic Sea and Lake Vättern, to illustrate how it can be used to identify potential keystone species and keystone links. We find that the keystone status of a species is closely linked to its body size. The analysis also suggests that communities are structurally and dynamically more sensitive to changes in the effects of prey on their consumers than in the effects of consumers on their prey. Moreover, we discuss how community sensitivity analysis can be used to study and compare the fragility of communities with different body size distributions by measuring the mean sensitivity or elasticity over all species or all interaction links in a community. We believe that the community sensitivity analysis developed here holds some promise for identifying species and links that are critical for the structural and dynamic robustness of ecological communities.

    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-66991 (URN)10.1111/j.1600-0706.2010.18864.x (DOI)000288753800005 ()
    Available from: 2011-03-24 Created: 2011-03-24 Last updated: 2013-01-29
    2. Rare but important: perturbations to uncommon species have disproportionately large impact on ecological communities
    Open this publication in new window or tab >>Rare but important: perturbations to uncommon species have disproportionately large impact on ecological communities
    Show others...
    (English)Manuscript (preprint) (Other academic)
    Abstract [en]

    The majority of species in the ecosystems of the world are rare. Because the contributions to community biomass and productivity of many of these species are small it has been suggested that loss of rare species should have relatively small ecological consequences. However, the extent to which rare species affect the structure and stability of ecosystems is largely unknown. Using a theoretical approach, based on analytical methods, we here   investigate how perturbations to rare as well as common species affect the structure (distribution of equilibrium abundances of species) and resilience (recovery rate) of complex ecological communities. We show that, contrary to expectation, resilience and structure of ecological communities are generally more sensitive to perturbations to rare than to common species. We find the explanation for this to lie in the cause of rarity: rare species tend to interact strongly, on a per capita basis, with other species. Our results suggest that many rare species are likely to fill important ecological roles in ecosystems.

    Keyword
    Community sensitivity analysis, species abundance, species importance, food webs, stability, resilience
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-88048 (URN)
    Available from: 2013-01-29 Created: 2013-01-29 Last updated: 2013-01-29Bibliographically approved
    3. Ecological communities are vulnerable to realistic extinction sequences
    Open this publication in new window or tab >>Ecological communities are vulnerable to realistic extinction sequences
    Show others...
    (English)Manuscript (preprint) (Other academic)
    Abstract [en]

    Loss of species will directly change the structure of ecological communities, which in turn may cause additional species loss (secondary extinctions) due to indirect effects (e.g. loss of resources or altered population dynamics). The vulnerability of food webs to repeated species loss is expected to be affected by food web topology, species interactions and the order in which species go extinct. Species traits such as body size, abundance and connectivity probably determine the vulnerability to extinction of species and, thus, the order in which species go primarily extinct. However, how different sequences of primary extinctions affect the vulnerability of food webs to secondary extinctions, when species abundances are allowed to respond dynamically, is not well understood. So far, only one study has incorporated species dynamics when assessing the effect of different extinction sequences on community structure, and only a limited number of extinction sequences have been evaluated. Here, using complex model food webs and including population dynamics, we analyze the effect of 33 extinction sequences on community structure using R50 (the proportion of primarily removed species needed to cause a 50% reduction in species richness) as a measure of community robustness to secondary extinctions. As expected, we find community structure to be highly vulnerable to removal of primary producers. More surprisingly, removing species based on traits that are strongly linked to the trophic position of species (such as large-bodied species, rare species, species with a high net effect, species with a high trophic position) are found to be as destructive as removing only primary producers. Such top-down oriented removal of species are often considered to correspond to realistic primary extinctions of species, but earlier studies, based on topological approaches, have not found such realistic extinction sequences to have any drastic effect on the remaining community. Thus, our result suggests that ecological communities could be more vulnerable to realistic extinction sequences than previously believed.

    Keyword
    Community structure, extinction sequence, food webs, species loss, community robustness
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-88050 (URN)
    Available from: 2013-01-29 Created: 2013-01-29 Last updated: 2013-01-29Bibliographically approved
    4. Using species traits to predict secondary extinctions during food web disassembly
    Open this publication in new window or tab >>Using species traits to predict secondary extinctions during food web disassembly
    Show others...
    (English)Manuscript (preprint) (Other academic)
    Abstract [en]

    Global change keeps pushing species towards extinction which results in altered structures of ecological communities. Consequently, the loss of certain species can trigger a cascade of secondary extinctions resulting in further degradation of the system. The importance of species for upholding the structure of communities may be linked to the traits of species. However, due to the altered structure of communities following species loss, the importance of species (and species traits) may change as the structure of the food web change. Using a dynamical approach and simulating species loss in complex model communities we analyze the potential importance of 11 species traits. We find that the most important trait varies for different degree of food web collapse and food web connectance. Though, as the most important traits of species usually are correlated we conclude that the importance of species traits is rather robust against structural changes in the communities (especially when only consumer species are targets of primarily extinctions). Interestingly, food webs display a collapse threshold (after the initial loss of approximately 25% of all species) from which secondary extinctions increases. Finally, consider only the loss of consumer species, the effect (number of secondary extinctions) on community structure caused by a large perturbation (species loss) is positively correlated to the response of food webs resulting from a small perturbation to the same species.

    Keyword
    Community structure, extinction sequence, food webs, species loss, community robustness
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-88052 (URN)
    Available from: 2013-01-29 Created: 2013-01-29 Last updated: 2013-01-29Bibliographically approved
  • 3.
    Berg, Sofia
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology . Linköping University, The Institute of Technology.
    Christianou, Maria
    Linköping University, Department of Physics, Chemistry and Biology, Biotechnology . Linköping University, The Institute of Technology.
    Jonsson, Tomas
    Research centre for Systems Biology, Univ. of Skövde, Sweden.
    Ebenman, Bo
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology . Linköping University, The Institute of Technology.
    Using sensitivity analysis to identify keystone species and keystone links in size-based food webs2011In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 120, no 4, 510-519 p.Article in journal (Refereed)
    Abstract [en]

    Human-induced alterations in the birth and mortality rates of species and in the strength of interactions within and between species can lead to changes in the structure and resilience of ecological communities. Recent research points to the importance of considering the distribution of body sizes of species when exploring the response of communities to such perturbations. Here, we present a new size-based approach for assessing the sensitivity and elasticity of community structure (species equilibrium abundances) and resilience (rate of return to equilibrium) to changes in the intrinsic growth rate of species and in the strengths of species interactions. We apply this approach on two natural systems, the pelagic communities of the Baltic Sea and Lake Vättern, to illustrate how it can be used to identify potential keystone species and keystone links. We find that the keystone status of a species is closely linked to its body size. The analysis also suggests that communities are structurally and dynamically more sensitive to changes in the effects of prey on their consumers than in the effects of consumers on their prey. Moreover, we discuss how community sensitivity analysis can be used to study and compare the fragility of communities with different body size distributions by measuring the mean sensitivity or elasticity over all species or all interaction links in a community. We believe that the community sensitivity analysis developed here holds some promise for identifying species and links that are critical for the structural and dynamic robustness of ecological communities.

  • 4.
    Berg, Sofia
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology. Linköping University, The Institute of Technology.
    Jonsson, Tomas
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology. Linköping University, The Institute of Technology.
    Hauzy, Céline
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology. Linköping University, The Institute of Technology.
    Säterberg, Torbjörn
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology. Linköping University, The Institute of Technology.
    Christianou, Maria
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology. Linköping University, The Institute of Technology.
    Yearsley, Jon
    School of Biology and Environmental Science, University College Dublin, Ireland.
    Ebenman, Bo
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology. Linköping University, The Institute of Technology.
    Rare but important: perturbations to uncommon species have disproportionately large impact on ecological communitiesManuscript (preprint) (Other academic)
    Abstract [en]

    The majority of species in the ecosystems of the world are rare. Because the contributions to community biomass and productivity of many of these species are small it has been suggested that loss of rare species should have relatively small ecological consequences. However, the extent to which rare species affect the structure and stability of ecosystems is largely unknown. Using a theoretical approach, based on analytical methods, we here   investigate how perturbations to rare as well as common species affect the structure (distribution of equilibrium abundances of species) and resilience (recovery rate) of complex ecological communities. We show that, contrary to expectation, resilience and structure of ecological communities are generally more sensitive to perturbations to rare than to common species. We find the explanation for this to lie in the cause of rarity: rare species tend to interact strongly, on a per capita basis, with other species. Our results suggest that many rare species are likely to fill important ecological roles in ecosystems.

  • 5.
    Berg, Sofia
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology. Linköping University, The Institute of Technology.
    Pimenov, Alexander
    Weierstrass Institute, Berlin, Germany.
    Palmer, Catherine
    Environmental Research Institute, University College Cork, Cork, Ireland.
    Emmerson, Mark
    Environmental Research Institute, University College Cork, Cork, Ireland.
    Jonsson, Tomas
    Department of Ecology, Swedish University of Agricultural Sciences, Uppsala, Sweden.
    Ecological communities are vulnerable to realistic extinction sequencesManuscript (preprint) (Other academic)
    Abstract [en]

    Loss of species will directly change the structure of ecological communities, which in turn may cause additional species loss (secondary extinctions) due to indirect effects (e.g. loss of resources or altered population dynamics). The vulnerability of food webs to repeated species loss is expected to be affected by food web topology, species interactions and the order in which species go extinct. Species traits such as body size, abundance and connectivity probably determine the vulnerability to extinction of species and, thus, the order in which species go primarily extinct. However, how different sequences of primary extinctions affect the vulnerability of food webs to secondary extinctions, when species abundances are allowed to respond dynamically, is not well understood. So far, only one study has incorporated species dynamics when assessing the effect of different extinction sequences on community structure, and only a limited number of extinction sequences have been evaluated. Here, using complex model food webs and including population dynamics, we analyze the effect of 33 extinction sequences on community structure using R50 (the proportion of primarily removed species needed to cause a 50% reduction in species richness) as a measure of community robustness to secondary extinctions. As expected, we find community structure to be highly vulnerable to removal of primary producers. More surprisingly, removing species based on traits that are strongly linked to the trophic position of species (such as large-bodied species, rare species, species with a high net effect, species with a high trophic position) are found to be as destructive as removing only primary producers. Such top-down oriented removal of species are often considered to correspond to realistic primary extinctions of species, but earlier studies, based on topological approaches, have not found such realistic extinction sequences to have any drastic effect on the remaining community. Thus, our result suggests that ecological communities could be more vulnerable to realistic extinction sequences than previously believed.

  • 6.
    Berg, Sofia
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology. Linköping University, The Institute of Technology. University of Skovde, Sweden.
    Pimenov, Alexander
    Weierstrass Institute, Germany; National University of Ireland University of Coll Cork, Ireland.
    Palmer, Catherine
    Weierstrass Institute, Germany.
    Emmerson, Mark
    Queens University of Belfast, North Ireland.
    Jonsson, Tomas
    University of Skovde, Sweden; Swedish University of Agriculture Science, Sweden.
    Ecological communities are vulnerable to realistic extinction sequences2015In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 124, no 4, 486-496 p.Article in journal (Refereed)
    Abstract [en]

    Loss of species will directly change the structure and potentially the dynamics of ecological communities, which in turn may lead to additional species loss (secondary extinctions) due to direct and/or indirect effects (e.g. loss of resources or altered population dynamics). Furthermore, the vulnerability of food webs to repeated species loss is expected to be affected by food web topology, species interactions, as well as the order in which species go extinct. Species traits such as body size, abundance and connectivity might determine a species vulnerability to extinction and, thus, the order in which species go primarily extinct. Yet, the sequence of primary extinctions, and their effects on the vulnerability of food webs to secondary extinctions, when species abundances are allowed to respond dynamically, has only recently become the focus of attention. Here, we analyse and compare topological and dynamical robustness to secondary extinctions of model food webs, in the face of 34 extinction sequences based on species traits. Although secondary extinctions are frequent in the dynamical approach and rare in the topological approach, topological and dynamical robustness tends to be correlated for many bottom-up directed, but not for top-down directed deletion sequences. Furthermore, removing species based on traits that are strongly positively correlated to the trophic position of species (such as large body size, low abundance, high net effect) is, under the dynamical approach, found to be as destructive as removing primary producers. Such top-down oriented removal of species are often considered to correspond to realistic extinction scenarios, but earlier studies, based on topological approaches, have found such extinction sequences to have only moderate effects on the remaining community. Thus, our result suggests that the structure of ecological communities, and therefore the integrity of important ecosystem processes could be more vulnerable to realistic extinction sequences than previously believed.

  • 7.
    Berg, Sofia
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology. Linköping University, The Institute of Technology.
    Pimenov, Alexander
    Weierstrass Institute, Berlin, Germany.
    Palmer, Catherine
    Environmental Research Institute, University College Cork, Cork, Ireland.
    Emmerson, Mark
    Environmental Research Institute, University College Cork, Cork, Ireland.
    Jonsson, Tomas
    Department of Ecology, Swedish University of Agricultural Sciences, Uppsala, Sweden.
    Using species traits to predict secondary extinctions during food web disassemblyManuscript (preprint) (Other academic)
    Abstract [en]

    Global change keeps pushing species towards extinction which results in altered structures of ecological communities. Consequently, the loss of certain species can trigger a cascade of secondary extinctions resulting in further degradation of the system. The importance of species for upholding the structure of communities may be linked to the traits of species. However, due to the altered structure of communities following species loss, the importance of species (and species traits) may change as the structure of the food web change. Using a dynamical approach and simulating species loss in complex model communities we analyze the potential importance of 11 species traits. We find that the most important trait varies for different degree of food web collapse and food web connectance. Though, as the most important traits of species usually are correlated we conclude that the importance of species traits is rather robust against structural changes in the communities (especially when only consumer species are targets of primarily extinctions). Interestingly, food webs display a collapse threshold (after the initial loss of approximately 25% of all species) from which secondary extinctions increases. Finally, consider only the loss of consumer species, the effect (number of secondary extinctions) on community structure caused by a large perturbation (species loss) is positively correlated to the response of food webs resulting from a small perturbation to the same species.

  • 8.
    Berlow, E.L.
    et al.
    University of California, White Mountain Research Station, Bishop, CA 93514, United States, Department of Integrative Biology, University of California, Berkeley, CA 94720, United States.
    Neutel, A.-M.
    Department of Environmental Sciences, Utrecht University, PO Box 80115, 3508 TC Utrecht, Netherlands.
    Cohen, J.E.
    Rockefeller Columbia Universities, Box 20, 1230 York Avenue, New York, NY 10021-6399, United States.
    De, Ruiter P.C.
    De Ruiter, P.C., Department of Environmental Sciences, Utrecht University, PO Box 80115, 3508 TC Utrecht, Netherlands.
    Ebenman, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology .
    Emmerson, M.
    Dept. of Zool., Ecol. and Plant Sci., University College Cork, Prospect Row, Cork, Eire, Ireland.
    Fox, J.W.
    NERC Centre for Population Biology, Imperial College, Silwood Park, Ascot, Berkshire SL5 7PY, United Kingdom.
    Jansen, V.A.A.
    School of Biological Sciences, Royal Holloway, University of London, Egham, Surrey TW20 0EX, United Kingdom.
    Jones, J.I.
    School of Biological Sciences, Queen Mary, University of London, Mile End Road, London E1 4NS, United Kingdom.
    Kokkoris, G.D.
    Department of Marine Sciences, University of the Aegean, University Hill, 81100 Mytilene, Lesvos Island, Greece.
    Logofet, D.O.
    Laboratory of Math. Ecology, IFARAN, Pyzhevsky Pereulok 3, Moscow, 119017, Russian Federation.
    Mckane, A.J.
    Department of Theoretical Physics, University of Manchester, Manchester M13 9 PL, United Kingdom.
    Montoya, J.M.
    Complex Systems Laboratory, IMIM - UPF (GRIB), Dr Aigvader 80, 08003 Barcelona, Spain.
    Petchey, O.
    Dept. of Animal and Plant Sciences, University of Sheffield, Sheffield S10 2TN, United Kingdom.
    Interaction strengths in food webs: Issues and opportunities2004In: Journal of Animal Ecology, ISSN 0021-8790, Vol. 73, no 3, 585-598 p.Article, review/survey (Refereed)
    Abstract [en]

    1. Recent efforts to understand how the patterning of interaction strength affects both structure and dynamics in food webs have highlighted several obstacles to productive synthesis. Issues arise with respect to goals and driving questions, methods and approaches, and placing results in the context of broader ecological theory. 2. Much confusion stems from lack of clarity about whether the questions posed relate to community-level patterns or to species dynamics, and to what authors actually mean by the term 'interaction strength'. Here, we describe the various ways in which this term has been applied and discuss the implications of loose terminology and definition for the development of this field. 3. Of particular concern is the clear gap between theoretical and empirical investigations of interaction strengths and food web dynamics. The ecological community urgently needs to explore new ways to estimate biologically reasonable model coefficients from empirical data, such as foraging rates, body size, metabolic rate, biomass distribution and other species traits. 4. Combining numerical and analytical modelling approaches should allow exploration of the conditions under which different interaction strengths metrics are interchangeable with regard to relative magnitude, system responses, and species identity. 5. Finally, the prime focus on predator-prey links in much of the research to date on interaction strengths in food webs has meant that the potential significance of nontrophic interactions, such as competition, facilitation and biotic disturbance, has been largely ignored by the food web community. Such interactions may be important dynamically and should be routinely included in future food web research programmes.

  • 9.
    Binzer, Amrei
    et al.
    J.F. Blumenbach Institute of Zoology and Anthropology, Georg-August University Göttingen, Germany.
    Brose, Ulrich
    J.F. Blumenbach Institute of Zoology and Anthropology, Georg-August University Göttingen, Germany.
    Curtsdotter, Alva
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology. Linköping University, The Institute of Technology.
    Eklöf, Anna
    Department of Ecology and Evolution, University of Chicago, United States.
    Rall, Björn C.
    J.F. Blumenbach Institute of Zoology and Anthropology, Georg-August University Göttingen, Germany.
    Riede, Jens O.
    J.F. Blumenbach Institute of Zoology and Anthropology, Georg-August University Göttingen, Germany.
    de Castro, Fransisco
    Institute for Biochemistry and Biology, University of Potsdam, Germany.
    The susceptibility of species to extinctions in model communities2011In: Basic and Applied Ecology, ISSN 1439-1791, E-ISSN 1618-0089, Vol. 12, no 7, 590-599 p.Article in journal (Refereed)
    Abstract [en]

    Despite the fact that the loss of a species from a community has the potential to cause a dramatic decline in biodiversity, for example through cascades of secondary extinctions, little is known about the factors contributing to the extinction risk of any particular species. Here we expand earlier modeling approaches using a dynamic food-web model that accounts for bottom-up as well as top-down effects. We investigate what factors influence a species’ extinction risk and time to extinction of the non-persistent species. We identified three basic properties that affect a species’ risk of extinction. The highest extinction risk is born by species with (1) low energy input (e.g. high trophic level), (2) susceptibility to the loss of energy pathways (e.g. specialists with few prey species) and (3) dynamic instability (e.g. low Hill exponent and reliance on homogeneous energy channels when feeding on similarly sized prey). Interestingly, and different from field studies, we found that the trophic level and not the body mass of a species influences its extinction risk. On the other hand, body mass is the single most important factor determining the time to extinction of a species, resulting in small species dying first. This suggests that in the field the trophic level might have more influence on the extinction risk than presently recognized.

  • 10.
    Binzer, Amrei
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology. Linköping University, Faculty of Science & Engineering. University of Gottingen, Germany.
    Guill, Christian
    University of Gottingen, Germany; University of Potsdam, Germany; University of Amsterdam, Netherlands.
    Rall, Bjoern C.
    University of Gottingen, Germany; German Centre Integrat Biodivers Research iDiv, Germany; University of Jena, Germany.
    Brose, Ulrich
    University of Gottingen, Germany; German Centre Integrat Biodivers Research iDiv, Germany; University of Jena, Germany.
    Interactive effects of warming, eutrophication and size structure: impacts on biodiversity and food-web structure2016In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 22, no 1, 220-227 p.Article in journal (Refereed)
    Abstract [en]

    Warming and eutrophication are two of the most important global change stressors for natural ecosystems, but their interaction is poorly understood. We used a dynamic model of complex, size-structured food webs to assess interactive effects on diversity and network structure. We found antagonistic impacts: Warming increases diversity in eutrophic systems and decreases it in oligotrophic systems. These effects interact with the community size structure: Communities of similarly sized species such as parasitoid-host systems are stabilized by warming and destabilized by eutrophication, whereas the diversity of size-structured predator-prey networks decreases strongly with warming, but decreases only weakly with eutrophication. Nonrandom extinction risks for generalists and specialists lead to higher connectance in networks without size structure and lower connectance in size-structured communities. Overall, our results unravel interactive impacts of warming and eutrophication and suggest that size structure may serve as an important proxy for predicting the community sensitivity to these global change stressors.

  • 11.
    Borrvall, Charlotte
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology . Linköping University, The Institute of Technology.
    Biodiversity and Species Extinctions in Model Food Webs2006Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Many of the earth’s ecosystems are experiencing large species losses due to human impacts such as habitat destruction and fragmentation, climate change, species invasions, pollution, and overfishing. Due to the complex interactions between species in food webs the extinction of one species could lead to a cascade of further extinctions and hence cause dramatic changes in species composition and ecosystem processes. The complexity of ecological systems makes it difficult to study them empirically. The systems often consist of large species numbers with lots of interactions between species. Investigating ecological communities within a theoretical approach, using mathematical models and computer simulations, is an alternative or a complement to experimental studies. This thesis is a collection of theoretical studies. We use model food webs in order to explore how biodiversity (species number) affects the response of communities to species loss (Paper I-III) and to environmental variability (Paper IV).

    In paper I and II we investigate the risk of secondary extinctions following deletion of one species. It is shown that resistance against additional species extinctions increases with redundancy (number of species per functional group) (Paper I) in the absence of competition between basal species but decreases with redundancy in the presence of competition between basal species (Paper II). It is further shown that food webs with low redundancy run the risk of losing a greater proportion of species following a species deletion in a deterministic environment but when demographic stochasticity is included the benefits of redundancy are largely lost (Paper II). This finding implies that in the construction of nature reserves the advantages of redundancy for conservation of communities may be lost if the reserves are small in size. Additionally, food webs show higher risks of further extinctions after the loss of basal species and herbivores than after the loss of top predators (Paper I and II).

    Secondary extinctions caused by a primary extinction and mediated through direct and indirect effects, are likely to occur with a time delay since the manifestation of indirect effects can take long time to appear. In paper III we show that the loss of a top predator leads to a significantly earlier onset of secondary extinctions in model communities than does the loss of a species from other trophic levels. If local secondary extinctions occur early they are less likely to be balanced by immigration of species from local communities nearby implying that secondary extinctions caused by the loss of top predators are less likely to be balanced by dispersal than secondary extinctions caused by the loss of other species. As top predators are vulnerable to human-induced disturbances on ecosystems in the first place, our results suggest that conservation of top predators should be a priority. Moreover, in most cases time to secondary extinction is shown to increase with species richness indicating the decay of ecological communities to be slower in species-rich than in species-poor communities.

    Apart from the human-induced disturbances that often force species towards extinction the environment is also, to a smaller or larger extent, varying over time in a natural way. Such environmental stochasticity influences the dynamics of populations. In paper IV we compare the responses of food webs of different sizes to environmental stochasticity. Species-rich webs are found to be more sensitive to environmental stochasticity. Particularly, species-rich webs lose a greater proportion of species than species-poor webs and they also begin losing species faster than species-poor webs. However, once one species is lost time to final extinction is longer in species-rich webs than in species-poor webs. We also find that the results differ depending on whether species respond similarly to environmental fluctuations or whether they are totally uncorrelated in their response. For a given species richness, communities with uncorrelated species responses run a considerable higher risk of losing a fixed proportion of species compared with communities with correlated species responses.

    List of papers
    1. Biodiversity lessens the risk of cascading extinction in model food webs
    Open this publication in new window or tab >>Biodiversity lessens the risk of cascading extinction in model food webs
    2000 (English)In: Ecology Letters, ISSN 1461-023X , Vol. 3, no 2, 131-136 p.Article in journal (Refereed) Published
    Abstract [en]

    Due to the complex interactions between species in food webs, the extinction of one species could lead to a cascade of further extinctions and hence cause dramatic changes in species composition and ecosystem processes. We found that the risk of additional species extinction, following the loss of one species in model food webs, decreases with the number of species per functional group. For a given number of species per functional group, the risk of further extinctions is highest when an autotroph is removed and lowest when a top predator is removed. In addition, stability decreases when the distribution of interaction strengths in the webs is changed from equal to skew (few strong and many weak links). We also found that omnivory appears to stabilize model food webs. Our results indicate that high biodiversity may serve as an insurance against radical ecosystem changes.

    Keyword
    Biodiversity, extinction • food webs, functional groups, redundancy, resistance, species deletion, stability
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-13855 (URN)10.1046/j.1461-0248.2000.00130.x (DOI)
    Available from: 2006-06-08 Created: 2006-06-08
    2. Community viability analysis: the response of ecological communities to species loss.
    Open this publication in new window or tab >>Community viability analysis: the response of ecological communities to species loss.
    2004 (English)In: Ecology, ISSN 0012-9658, Vol. 85, no 9, 2591-2600 p.Article in journal (Refereed) Published
    Abstract [en]

    The loss of a species from an ecological community can set up a cascade of secondary extinctions that in the worst case could lead to the collapse of the community. Both deterministic and stochastic mechanisms may be involved in such secondary extinctions. To investigate the extent of secondary extinctions in ecological communities following the loss of a species, we here develop a community viability analysis. We introduce a measure called the “quasi-collapse risk” that is defined as the probability that the number of species in a community falls below some defined value within a fixed period of time following the loss of a species. We develop deterministic and stochastic methods for finding post-extinction communities. We use these methods to investigate the relationship between diversity (species richness) and quasi-collapse risks in model communities. It is shown that, in a deterministic context, communities with more species within trophic levels have a larger fraction of species remaining in post-extinction communities. This benefit of species richness is to a large extent lost in the presence of demographic stochasticity. The reason for this is a negative relationship between population density and species diversity. We also show that communities become increasingly triangular in shape as secondary extinctions take place, due to greater extinction risk of species at higher trophic levels. We argue that this new approach holds some promise for identifying fragile ecosystems and keystone species.

    Keyword
    collapse risk, community viability analysis, demographic stochasticity, individual-based models, permanence, redundancy, secondary extinctions, species diversity, species loss
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-13856 (URN)10.1890/03-8018 (DOI)
    Available from: 2006-06-08 Created: 2006-06-08 Last updated: 2009-05-08
    3. Early onset of secondary extinctions in ecological communities following the loss of top predators
    Open this publication in new window or tab >>Early onset of secondary extinctions in ecological communities following the loss of top predators
    2006 (English)In: Ecology Letters, ISSN 1461-023X, Vol. 9, no 4, 435-442 p.Article in journal (Refereed) Published
    Abstract [en]

    The large vulnerability of top predators to human-induced disturbances on ecosystems is a matter of growing concern. Because top predators often exert strong influence on their prey populations their extinction can have far-reaching consequences for the structure and functioning of ecosystems. It has, for example, been observed that the local loss of a predator can trigger a cascade of secondary extinctions. However, the time lags involved in such secondary extinctions remain unexplored. Here we show that the loss of a top predator leads to a significantly earlier onset of secondary extinctions in model communities than does the loss of a species from other trophic levels. Moreover, in most cases time to secondary extinction increases with increasing species richness. If local secondary extinctions occur early they are less likely to be balanced by immigration of species from local communities nearby. The implications of these results for community persistence and conservation priorities are discussed.

    Keyword
    Ecological community, food web, relaxation time, secondary extinction, species interactions, species loss, species richness, top predators, trophic level
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-13857 (URN)10.1111/j.1461-0248.2006.00893.x (DOI)
    Available from: 2006-06-08 Created: 2006-06-08
    4. Biodiversity and persistence of ecological communities in a stochastic environment
    Open this publication in new window or tab >>Biodiversity and persistence of ecological communities in a stochastic environment
    Manuscript (Other academic)
    Identifiers
    urn:nbn:se:liu:diva-13858 (URN)
    Available from: 2006-06-08 Created: 2006-06-08 Last updated: 2010-01-13
  • 12.
    Borrvall, Charlotte
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology .
    Christianou, Maria
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology .
    Ebenman, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology .
    Biodiversity Decreases the risk of Collapse2005In: Systems shocks - Systems resilience, The 2000 Abisko Workshop,2000, London: World Scientific , 2005, 209- p.Conference paper (Refereed)
  • 13.
    Borrvall, Charlotte
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology .
    Ebenman, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology .
    Biodiversity and persistence of ecological communities in variable environments2008In: Ecological Complexity: An International Journal on Biocomplexity in the Environment and Theoretical Ecology, ISSN 1476-945X, Vol. 5, 99-105 p.Article in journal (Refereed)
  • 14.
    Borrvall, Charlotte
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology . Linköping University, The Institute of Technology.
    Ebenman, Bo
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology . Linköping University, The Institute of Technology.
    Early onset of secondary extinctions in ecological communities following the loss of top predators2006In: Ecology Letters, ISSN 1461-023X, Vol. 9, no 4, 435-442 p.Article in journal (Refereed)
    Abstract [en]

    The large vulnerability of top predators to human-induced disturbances on ecosystems is a matter of growing concern. Because top predators often exert strong influence on their prey populations their extinction can have far-reaching consequences for the structure and functioning of ecosystems. It has, for example, been observed that the local loss of a predator can trigger a cascade of secondary extinctions. However, the time lags involved in such secondary extinctions remain unexplored. Here we show that the loss of a top predator leads to a significantly earlier onset of secondary extinctions in model communities than does the loss of a species from other trophic levels. Moreover, in most cases time to secondary extinction increases with increasing species richness. If local secondary extinctions occur early they are less likely to be balanced by immigration of species from local communities nearby. The implications of these results for community persistence and conservation priorities are discussed.

  • 15.
    Borrvall, Charlotte
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology . Linköping University, The Institute of Technology.
    Ebenman, Bo
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology . Linköping University, The Institute of Technology.
    Jonsson, Tomas
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Biodiversity lessens the risk of cascading extinction in model food webs2000In: Ecology Letters, ISSN 1461-023X , Vol. 3, no 2, 131-136 p.Article in journal (Refereed)
    Abstract [en]

    Due to the complex interactions between species in food webs, the extinction of one species could lead to a cascade of further extinctions and hence cause dramatic changes in species composition and ecosystem processes. We found that the risk of additional species extinction, following the loss of one species in model food webs, decreases with the number of species per functional group. For a given number of species per functional group, the risk of further extinctions is highest when an autotroph is removed and lowest when a top predator is removed. In addition, stability decreases when the distribution of interaction strengths in the webs is changed from equal to skew (few strong and many weak links). We also found that omnivory appears to stabilize model food webs. Our results indicate that high biodiversity may serve as an insurance against radical ecosystem changes.

  • 16.
    Brommesson, Peter
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology. Linköping University, Faculty of Science & Engineering.
    Wennergren, Uno
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology. Linköping University, Faculty of Science & Engineering.
    Lindström, Tom
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology. Linköping University, Faculty of Science & Engineering.
    Spatiotemporal Variation in Distance Dependent Animal Movement Contacts: One Size Doesnt Fit All2016In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 11, no 10, e0164008- p.Article in journal (Refereed)
    Abstract [en]

    The structure of contacts that mediate transmission has a pronounced effect on the outbreak dynamics of infectious disease and simulation models are powerful tools to inform policy decisions. Most simulation models of livestock disease spread rely to some degree on predictions of animal movement between holdings. Typically, movements are more common between nearby farms than between those located far away from each other. Here, we assessed spatiotemporal variation in such distance dependence of animal movement contacts from an epidemiological perspective. We evaluated and compared nine statistical models, applied to Swedish movement data from 2008. The models differed in at what level ( if at all), they accounted for regional and/or seasonal heterogeneities in the distance dependence of the contacts. Using a kernel approach to describe how probability of contacts between farms changes with distance, we developed a hierarchical Bayesian framework and estimated parameters by using Markov Chain Monte Carlo techniques. We evaluated models by three different approaches of model selection. First, we used Deviance Information Criterion to evaluate their performance relative to each other. Secondly, we estimated the log predictive posterior distribution, this was also used to evaluate their relative performance. Thirdly, we performed posterior predictive checks by simulating movements with each of the parameterized models and evaluated their ability to recapture relevant summary statistics. Independent of selection criteria, we found that accounting for regional heterogeneity improved model accuracy. We also found that accounting for seasonal heterogeneity was beneficial, in terms of model accuracy, according to two of three methods used for model selection. Our results have important implications for livestock disease spread models where movement is an important risk factor for between farm transmission. We argue that modelers should refrain from using methods to simulate animal movements that assume the same pattern across all regions and seasons without explicitly testing for spatiotemporal variation.

  • 17.
    Brose, Ulrich
    et al.
    German Centre for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig, 04103, Leipzig, Germany 2 Faculty of Biology and Pharmacy, Institute of Ecology, Friedrich Schiller University Jena, 07743, Jena, Germany.
    Blanchard, Julia L.
    Institute for Marine and Antarctic Studies and Centre for Marine Socioecology, University of Tasmania, 20 Castray Esplanade, Battery Point TAS 7004 Australia.
    Eklöf, Anna
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology. Linköping University, Faculty of Science & Engineering.
    Galiana, Nuria
    Ecological Networks and Global Change Group, Experimental Ecology Station, Centre National de la Recherche Scientifique, 09200, Moulis, France.
    Hartvig, Martin
    Center for Macroecology, Evolution and Climate, Natural History Museum of Denmark, University of Copenhagen, DK-2100, Copenhagen, Denmark 7 National Institute of Aquatic Resources, Technical University of Denmark, DK-2920, Charlottenlund, Denmark 8 Systemic Conservation Biology Group, J.F. Blumenbach Institute of Zoology and Anthropology, Georg-August University of Göttingen, 37073, Göttingen, Germany.
    Hirt, Myriam R.
    German Centre for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig, 04103, Leipzig, Germany 2 Faculty of Biology and Pharmacy, Institute of Ecology, Friedrich Schiller University Jena, 07743, Jena, Germany.
    Kalinkat, Gregor
    Department of Biology and Ecology of Fishes, Leibniz-Institute of Freshwater Ecology and Inland Fisheries, 12587, Berlin, Germany 10 Department of Fish Ecology and Evolution, Eawag, 6047, Kastanienbaum, Switzerland.
    Nordström, MArie C.
    Environmental and Marine Biology, Åbo Akademi University, FI-20520, Åbo, Finland.
    O'Gorman, Eoin J.
    Imperial College London, Silwood Park Campus, Buckhurst Road, Ascot, Berkshire, SL5 7PY, UK.
    Rall, Björn C.
    German Centre for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig, 04103, Leipzig, Germany 2 Faculty of Biology and Pharmacy, Institute of Ecology, Friedrich Schiller University Jena, 07743, Jena, Germany.
    Schneider, Florian D.
    Institut des Sciences de l’Evolution, Universit´e Montpellier, CNRS, IRD, EPHE, CC065, 34095, Montpellier Cedex 05, France.
    Thébault, Elisa
    Institute of Ecology and Environmental Sciences - Paris, UMR 7618 (UPMC, CNRS, IRD, INRA, UPEC, Paris Diderot), Universit´e Pierre et Marie Curie, 75005, Paris, France.
    Jacob, Ute
    Department of Biology, Institute for Hydrobiology and Fisheries Science, Center for Earth System Research and Sustainability (CEN), KlimaCampus, University of Hamburg, 22767, Hamburg, Germany.
    Predicting the consequences of species lossusing size-structured biodiversity approaches2017In: Biological Reviews, ISSN 1464-7931, E-ISSN 1469-185X, Vol. 92, no 2, 684-697 p.Article, review/survey (Refereed)
    Abstract [en]

    Understanding the consequences of species loss in complex ecological communities is one of the great challenges in current biodiversity research. For a long time, this topic has been addressed by traditional biodiversity experiments. Most of these approaches treat species as trait-free, taxonomic units characterizing communities only by species number without accounting for species traits. However, extinctions do not occur at random as there is a clear correlation between extinction risk and species traits. In this review, we assume that large species will be most threatened by extinction and use novel allometric and size-spectrum concepts that include body mass as a primary species trait at the levels of populations and individuals, respectively, to re-assess three classic debates on the relationships between biodiversity and (i) food-web structural complexity, (ii) community dynamic stability, and (iii) ecosystem functioning. Contrasting current expectations, size-structured approaches suggest that the loss of large species, that typically exploit most resource species, may lead to future food webs that are less interwoven and more structured by chains of interactions and compartments. The disruption of natural body-mass distributions maintaining food-web stability may trigger avalanches of secondary extinctions and strong trophic cascades with expected knock-on effects on the functionality of the ecosystems. Therefore, we argue that it is crucial to take into account body size as a species trait when analysing the consequences of biodiversity loss for natural ecosystems. Applying size-structured approaches provides an integrative ecological concept that enables a better understanding of each species' unique role across communities and the causes and consequences of biodiversity loss.

  • 18.
    Brose, Ulrich
    et al.
    Technical University of Darmstadt, Germany.
    Pavao-Zuckerman, Mitchell
    University of Arizona, Tucson, Arizona, USA.
    Eklöf, Anna
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology. Linköping University, The Institute of Technology.
    Bengtsson, Janne
    Swedish University of Agricultural Sciences, Uppsala, Sweden.
    Berg, Matty P.
    Vrije Universiteit Amsterdam, The Netherlands.
    Cousins, Steven H.
    Cranfield University, United Kingdom.
    Mulder, Christian
    National Institute for Public Health and the Environment (RIVM), Bilthoven, The Netherlands.
    Verhoef, Herman A.
    Vrije Universiteit Amsterdam, The Netherlands.
    Wolters, Volkmar
    Justus-Liebig-University, Giessen, Germany.
    Spatial aspects of food webs2005In: Dynamic Food Webs: Multispecies Assemblages, Ecosystem Development and Environmental Change / [ed] P.C. deRuiter, V. Wolters & J.C. Moore, London, UK: Elsevier, 2005, Vol. 3, 463-469 p.Conference paper (Refereed)
    Abstract [en]

    Aspects of spatial scale have until recently been largely ignored in empirical and theoretical food web studies (e.g., Cohen & Briand 1984, Martinez 1992, but see Bengtsson et al. 2002, Bengtsson & Berg, this book). Most ecologists tend to conceptualize and represent food webs as static representations of communities, depicting a community assemblage as sampled at a particular point in time, or highly aggregated trophic group composites over broader scales of time and space (Polis et al. 1996). Moreover, most researchers depict potential food webs, which contain all species sampled and all potential trophic links based on literature reviews, several sampling events, or laboratory feeding trials. In reality, however, not all these potential feeding links are realized as not all species co-occur, and not all samples in space or time can contain all species (Schoenly & Cohen 1991), hence, yielding a variance of food web architecture in space (Brose et al. 2004). In recent years, food web ecologists have recognized that food webs are open systems – that are influence by processes in adjacent systems – and spatially heterogeneous (Polis et al. 1996). This influence of adjacent systems can be bottom-up, due to allochthonous inputs of resources (Polis & Strong 1996, Huxel & McCann 1998, Mulder & De Zwart 2003), or top-down due to the regular or irregular presence of top predators (e.g., Post et al. 2000, Scheu 2001). However, without a clear understanding of the size of a system and a definition of its boundaries it is not possible to judge if flows are internal or driven by adjacent systems. Similarly, the importance of allochthony is only assessable when the balance of inputs and outputs are known relative to the scale and throughputs within the system itself. At the largest scale of the food web – the home range of a predator such as wolf, lion, shark or eagle of roughly 50 km2 to 300 km2 –the balance of inputs and outputs caused by wind and movement of water may be small compared to the total trophic flows within the home range of the large predator (Cousins 1990). Acknowledging these issues of space, Polis et al (1996) argued that progress toward the next phase of food web studies would require addressing spatial and temporal processes. Here, we present a conceptual framework with some nuclei about the role of space in food web ecology. Although we primarily address spatial aspects, this framework is linked to a more general concept of spatio-temporal scales of ecological research.

  • 19.
    Buhnerkempe, Michael G.
    et al.
    Colorado State University, CO 80523 USA .
    Tildesley, Michael J.
    University of Warwick, England .
    Lindström, Tom
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology. Linköping University, The Institute of Technology.
    Grear, Daniel A.
    Colorado State University, CO 80523 USA .
    Portacci, Katie
    US Anim and Plant Health Inspect Serv, CO USA US Anim and Plant Health Inspect Serv, CO USA .
    Miller, Ryan S.
    US Anim and Plant Health Inspect Serv, CO USA US Anim and Plant Health Inspect Serv, CO USA .
    Lombard, Jason E.
    US Anim and Plant Health Inspect Serv, CO USA US Anim and Plant Health Inspect Serv, CO USA .
    Werkman, Marleen
    University of Warwick, England .
    Keeling, Matt J.
    University of Warwick, England .
    Wennergren, Uno
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology. Linköping University, The Institute of Technology.
    Webb, Colleen T.
    Colorado State University, CO 80523 USA .
    The Impact of Movements and Animal Density on Continental Scale Cattle Disease Outbreaks in the United States2014In: PLoS ONE, ISSN 1932-6203, Vol. 9, no 3, 0091724- p.Article in journal (Refereed)
    Abstract [en]

    Globalization has increased the potential for the introduction and spread of novel pathogens over large spatial scales necessitating continental-scale disease models to guide emergency preparedness. Livestock disease spread models, such as those for the 2001 foot-and-mouth disease (FMD) epidemic in the United Kingdom, represent some of the best case studies of large-scale disease spread. However, generalization of these models to explore disease outcomes in other systems, such as the United Statess cattle industry, has been hampered by differences in system size and complexity and the absence of suitable livestock movement data. Here, a unique database of US cattle shipments allows estimation of synthetic movement networks that inform a near-continental scale disease model of a potential FMD-like (i.e., rapidly spreading) epidemic in US cattle. The largest epidemics may affect over one-third of the US and 120,000 cattle premises, but cattle movement restrictions from infected counties, as opposed to national movement moratoriums, are found to effectively contain outbreaks. Slow detection or weak compliance may necessitate more severe state-level bans for similar control. Such results highlight the role of large-scale disease models in emergency preparedness, particularly for systems lacking comprehensive movement and outbreak data, and the need to rapidly implement multi-scale contingency plans during a potential US outbreak.

  • 20.
    Christianou, Maria
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology. Linköping University, The Institute of Technology.
    Interaction strength and responses of ecological communities to disturbances2006Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Ecological communities are continuously exposed to natural or anthropogenic disturbances of varied intensity and frequency. The way communities respond to disturbances can depend on various factors, such as number of species, structural characteristics of the community, stability properties, species characteristics and the nature of the disturbance. This thesis is a collection of theoretical studies on how ecological communities respond to different kind of disturbances, mainly in relation to interaction strength between species, a measure of how strongly or weakly species interact with each other.

    A major disturbance for natural communities is the loss of a species. Although species extinctions is a natural process in the geological time scale, it has lately been dangerously accelerated due to human activities and interferences. Extinction of a species can have dramatic consequences for the community, can trigger a cascade of secondary species extinction and can even lead to community collapse. In Paper I, we identify species whose loss can trigger a large number of secondary extinctions (namely keystone species), species that are particularly vulnerable to become extinct following the loss of another species and mechanisms behind the sequence of secondary extinctions. We also highlight the fact that the keystone status of a species can be context dependent, that is, it is dependent on the structure of the community where it is embedded.

    Although the global extinction of a species is an irreversible process, in cases of local extinction, conservation and restoration plans can include reintroduction of the species to their former location. Such reintroduction or translocation attempts often fail, due to characteristics of the reintroduced species and to changes in the community structure caused by the initial loss of the species (Paper II ). Using model communities we show that this risk of reintroduction failure can be high - even in cases where the initial species loss did not cause any secondary extinctions - and it differs between attempts to reintroduce weakly or strongly interacting species (Paper II ).

    Disturbances are not always as profound as species extinction. Human activities and environmental changes can cause small and permanent changes in birth and mortality rates of species and in the strength of interaction between species. Such disturbances can change the stability properties of ecological communities making them more vulnerable to further disturbances. In Paper III, we derive analytical expressions for the sensitivity of resilience to changes in the intrinsic growth rate of species and in the strength of interaction links. We also apply the method to model communities and identify keystone species and links, i.e. species and links whose small disturbance would cause large changes in community resilience. We found that changes in the growth rate of strongly interacting species have a larger impact on resilience than changes in the growth rate of weakly interacting species, which is in line with the main findings of the species deletion study (Paper I ).

    Community complexity - mainly expressed as number of species and links - was one of the first community characteristics to be related to stability properties and the way communities respond to disturbances. Many theoretical works support the hypothesis that complexity reduces stability, contradicting intuition, observation and many experimental studies. In Paper IV, we state that this could be, at least partly, due to methodological misconceptions and misinterpretations. We propose a new sampling method for parameterizing model communities and we highlight the importance of feasibility of model communities (all species densities are strictly positive), for a more proper estimation of stability probability of communities with different degrees of complexity.

    List of papers
    1. Keystone species and vulnerable species in ecological communities: strong or weak interactors?
    Open this publication in new window or tab >>Keystone species and vulnerable species in ecological communities: strong or weak interactors?
    2005 (English)In: Journal of Theoretical Biology, ISSN 0022-5193, Vol. 35, no 1, 95-103 p.Article in journal (Refereed) Published
    Abstract [en]

    The loss of a species from an ecological community can trigger a cascade of secondary extinctions. The probability of secondary extinction to take place and the number of secondary extinctions are likely to depend on the characteristics of the species that is lost—the strength of its interactions with other species—as well as on the distribution of interaction strengths in the whole community. Analysing the effects of species loss in model communities we found that removal of the following species categories triggered, on average, the largest number of secondary extinctions: (a) rare species interacting strongly with many consumers, (b) abundant basal species interacting weakly with their consumers and (c) abundant intermediate species interacting strongly with many resources. We also found that the keystone status of a species with given characteristics was context dependent, that is, dependent on the structure of the community where it was embedded. Species vulnerable to secondary extinctions were mainly species interacting weakly with their resources and species interacting strongly with their consumers.

    Keyword
    Species loss; Keystone species; Interaction strength; Community dynamics; Permanence; Secondary extinction
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-14053 (URN)10.1016/j.jtbi.2004.12.022 (DOI)
    Available from: 2006-10-04 Created: 2006-10-04
    2. Prospects and risks of species reintroductions: a community ecological perspective
    Open this publication in new window or tab >>Prospects and risks of species reintroductions: a community ecological perspective
    (English)Manuscript (Other academic)
    Abstract [en]

    For many threatened species reintroduction of captive-reared individuals into the wild may offer the only hope of preventing global extinction. However, attempts to reintroduce a species into an ecological community from which it has once gone extinct often fail. This can be due to captivity-induced genetic and behavioural changes in the species itself. Here we argue that also changes in the structure of the community caused by the initial loss of the species can hinder its subsequent reintroduction. Due to the interdependences amongspecies in ecological communities the local extinction of a species leads to changes in the densities and strength of interactions among the remaining species in the community and sometimes even to a cascade of secondary extinctions. Such alterations in the structure of a community caused by the initial extinction of the species might make it impossible for the species to reinvade at a later stage. Here we show, using models of multitrophic communities, that the risk of reintroduction failure can be high and that it differs between species belonging to different trophic levels and between weakly and strongly interacting species. Specifically, there is a high risk of reintroduction failure for primary producer species and weakly interacting consumer species. We also find the risk that the reintroduction will cause new extinctions to be higher in communities where the initial loss triggered secondary extinctions. In the worst case extinctions caused by the reintroduction may lead to the subsequent extinction of the reintroduced species itself. This risk is not negligible implicating that reintroductions might sometimes aggravate the state of local communities.

    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-14054 (URN)
    Available from: 2006-10-04 Created: 2006-10-04 Last updated: 2012-11-14
    3. Sensitivity analysis at the community level
    Open this publication in new window or tab >>Sensitivity analysis at the community level
    2006 (English)Manuscript (preprint) (Other academic)
    Abstract [en]

    Human-induced changes in the birth and mortality rates of species and in the strength of interactions within and between species can lead to changes in the resilience of ecological communities. Here we derive analytical expressions for the sensitivity of community resilience to changes in the intrinsic growth rate of species and in the strengths of interaction links. These new methods are applied on model communities to illustrate how they can be used to identify keystone species and keystone links - keystone species and keystone links in the sensethat small changes in their growth rates and strengths, respectively, will have large effects on the resilience of the community. We find that small changes in the intrinsic growth rates of rare species (e.g. top predators) and strongly interacting species have larger effect on resilience than changes in the growth rates of abundant species and weakly interacting species. Moreover, we find that small changes in the strength of weak interaction links cause larger changes in resilience than changes in the strength of strong links. We believe that thecommunity sensitivity analysis developed here holds some promise for identifying species and links that are critical for the resilience of ecological communities.

    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-14055 (URN)
    Available from: 2006-10-04 Created: 2006-10-04 Last updated: 2012-11-14
    4. Diversity-stability relation from a methodological point of view
    Open this publication in new window or tab >>Diversity-stability relation from a methodological point of view
    (English)Manuscript (Other academic)
    Abstract [en]

    The complexity - stability relation has been a central issue in ecology for a long time. Both theoretical and empirical studies have been investigating whether complexity promotes stability or not, which could be the underlying mechanisms creating a positive or negative cmnplexity-stability relation and which are the structures, characteristics and constraints that would allow complex ecological systems to persist and be stable. In this paper we approach the subject from amethodological point of view. We study the effect of parameterizing the communities in a certain way and illustrate the effect of treating feasibility (i.e. densities of all species are strictly positive) separately from stability. We observe that increasing number of species in the communities requires a more skewed interaction strength distribution toward weak interactions, in order for the communities to theoretically exist. Using model Lotka-Volterra competition communities we illustrate that probability of feasibility decreases with increasing interaction strength and number of species in the community. However, forfeasible systems we find that local stability probability and resilience do not significantly differ between communities with few or many species, in contrast with earlier studies that, did not account for feasibility and concluded that species poor communities had higher probability of being locally stable than species rich communities.

    Keyword
    Local stability, resilience, feasibility, Lotka-Volterra model, competition community, Central Limit Theorem
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-14056 (URN)
    Note

    Alternative title: Complexity - Stability relation from a methodological point of view

    Available from: 2006-10-04 Created: 2006-10-04 Last updated: 2012-11-14
  • 21.
    Christianou, Maria
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology . Linköping University, The Institute of Technology.
    Ebenman, Bo
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology . Linköping University, The Institute of Technology.
    Keystone species and vulnerable species in ecological communities: strong or weak interactors?2005In: Journal of Theoretical Biology, ISSN 0022-5193, Vol. 35, no 1, 95-103 p.Article in journal (Refereed)
    Abstract [en]

    The loss of a species from an ecological community can trigger a cascade of secondary extinctions. The probability of secondary extinction to take place and the number of secondary extinctions are likely to depend on the characteristics of the species that is lost—the strength of its interactions with other species—as well as on the distribution of interaction strengths in the whole community. Analysing the effects of species loss in model communities we found that removal of the following species categories triggered, on average, the largest number of secondary extinctions: (a) rare species interacting strongly with many consumers, (b) abundant basal species interacting weakly with their consumers and (c) abundant intermediate species interacting strongly with many resources. We also found that the keystone status of a species with given characteristics was context dependent, that is, dependent on the structure of the community where it was embedded. Species vulnerable to secondary extinctions were mainly species interacting weakly with their resources and species interacting strongly with their consumers.

  • 22.
    Christianou, Maria
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology. Linköping University, The Institute of Technology.
    Ebenman, Bo
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology. Linköping University, The Institute of Technology.
    Prospects and risks of species reintroductions: a community ecological perspectiveManuscript (Other academic)
    Abstract [en]

    For many threatened species reintroduction of captive-reared individuals into the wild may offer the only hope of preventing global extinction. However, attempts to reintroduce a species into an ecological community from which it has once gone extinct often fail. This can be due to captivity-induced genetic and behavioural changes in the species itself. Here we argue that also changes in the structure of the community caused by the initial loss of the species can hinder its subsequent reintroduction. Due to the interdependences amongspecies in ecological communities the local extinction of a species leads to changes in the densities and strength of interactions among the remaining species in the community and sometimes even to a cascade of secondary extinctions. Such alterations in the structure of a community caused by the initial extinction of the species might make it impossible for the species to reinvade at a later stage. Here we show, using models of multitrophic communities, that the risk of reintroduction failure can be high and that it differs between species belonging to different trophic levels and between weakly and strongly interacting species. Specifically, there is a high risk of reintroduction failure for primary producer species and weakly interacting consumer species. We also find the risk that the reintroduction will cause new extinctions to be higher in communities where the initial loss triggered secondary extinctions. In the worst case extinctions caused by the reintroduction may lead to the subsequent extinction of the reintroduced species itself. This risk is not negligible implicating that reintroductions might sometimes aggravate the state of local communities.

  • 23.
    Christianou, Maria
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology. Linköping University, The Institute of Technology.
    Ebenman, Bo
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology. Linköping University, The Institute of Technology.
    Sensitivity analysis at the community level2006Manuscript (preprint) (Other academic)
    Abstract [en]

    Human-induced changes in the birth and mortality rates of species and in the strength of interactions within and between species can lead to changes in the resilience of ecological communities. Here we derive analytical expressions for the sensitivity of community resilience to changes in the intrinsic growth rate of species and in the strengths of interaction links. These new methods are applied on model communities to illustrate how they can be used to identify keystone species and keystone links - keystone species and keystone links in the sensethat small changes in their growth rates and strengths, respectively, will have large effects on the resilience of the community. We find that small changes in the intrinsic growth rates of rare species (e.g. top predators) and strongly interacting species have larger effect on resilience than changes in the growth rates of abundant species and weakly interacting species. Moreover, we find that small changes in the strength of weak interaction links cause larger changes in resilience than changes in the strength of strong links. We believe that thecommunity sensitivity analysis developed here holds some promise for identifying species and links that are critical for the resilience of ecological communities.

  • 24.
    Christianou, Maria
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology. Linköping University, The Institute of Technology.
    Kokkoris, Giorgos D.
    Dept. of Marine Sciences, Faculty of Environment, University of the Aegean, Mytilene, Lesvos Island, Greece.
    Diversity-stability relation from a methodological point of viewManuscript (Other academic)
    Abstract [en]

    The complexity - stability relation has been a central issue in ecology for a long time. Both theoretical and empirical studies have been investigating whether complexity promotes stability or not, which could be the underlying mechanisms creating a positive or negative cmnplexity-stability relation and which are the structures, characteristics and constraints that would allow complex ecological systems to persist and be stable. In this paper we approach the subject from amethodological point of view. We study the effect of parameterizing the communities in a certain way and illustrate the effect of treating feasibility (i.e. densities of all species are strictly positive) separately from stability. We observe that increasing number of species in the communities requires a more skewed interaction strength distribution toward weak interactions, in order for the communities to theoretically exist. Using model Lotka-Volterra competition communities we illustrate that probability of feasibility decreases with increasing interaction strength and number of species in the community. However, forfeasible systems we find that local stability probability and resilience do not significantly differ between communities with few or many species, in contrast with earlier studies that, did not account for feasibility and concluded that species poor communities had higher probability of being locally stable than species rich communities.

  • 25.
    Cirtwill, Alyssa
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology. Linköping University, Faculty of Science & Engineering. University of Canterbury, New Zealand; University of Otago, New Zealand.
    Lagrue, Clement
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering.
    Poulin, Robert
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering.
    Stouffer, Daniel B.
    University of Canterbury, New Zealand.
    Host taxonomy constrains the properties of trophic transmission routes for parasites in lake food webs2017In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 98, no 9, 2401-2412 p.Article in journal (Refereed)
    Abstract [en]

    Some parasites move from one host to another via trophic transmission, the consumption of the parasite (inside its current host) by its future host. Feeding links among free-living species can thus be understood as potential transmission routes for parasites. As these links have different dynamic and structural properties, they may also vary in their effectiveness as trophic transmission routes. That is, some links may be better than others in allowing parasites to complete their complex life cycles. However, not all links are accessible to parasites as most are restricted to a small number of host taxa. This restriction means that differences between links involving host and non-host taxa must be considered when assessing whether transmission routes for parasites have different food web properties than other links. Here we use four New Zealand lake food webs to test whether link properties (contribution of a link to the predators diet, prey abundance, prey biomass, amount of biomass transferred, centrality, and asymmetry) affect trophic transmission of parasites. Critically, we do this using both models that neglect the taxonomy of free-living species and models that explicitly include information about which free-living species are members of suitable host taxa. Although the best-fit model excluding taxonomic information suggested that transmission routes have different properties than other feeding links, when including taxonomy, the best-fit model included only an intercept. This means that the taxonomy of free-living species is a key determinant of parasite transmission routes and that food-web properties of transmission routes are constrained by the properties of host taxa. In particular, many intermediate hosts (prey) attain high biomasses and are involved in highly central links while links connecting intermediate to definitive (predator) hosts tend to be dynamically weak.

  • 26.
    Curtsdotter, Alva
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology. Linköping University, The Institute of Technology.
    Extinctions in Ecological Communities: direct and indirect effects of perturbation on biodiversity2014Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In the dawning of what may become Earth’s 6th mass extinction the topic of this thesis, understanding extinction processes and what determines the magnitude of species loss, has become only too relevant. The number of known extinctions (~850) during the last centuries translates to extinction rates elevated above the background rate, matching those of previous mass extinction events. The main drivers of these extinctions have been human land use, introduction of exotic species and overexploitation. Under continued anthropogenic pressure and climate change, the current extinction rates are predicted to increase tenfold.

    Large perturbations, such as the extinction drivers mentioned above, affects species directly, causing a change in their abundance. As species are not isolated, but connected to each other through a multitude of interactions, the change in abundance of one species can in turn affect others. Thus, in addition to the direct effect, a perturbation can affect a species indirectly through the ecological network in which the species is embedded. With this thesis, I wish to contribute to our basic understanding of these indirect effects and the role they play in determining the magnitude of species loss. All the studies included here are so called in silico experiments, using mathematical models to describe ecological communities and computer simulations to observe the response of these communities to perturbation.

    When a perturbation is severe enough, a species will be driven to extinction. The loss of a species from a system is in itself a large perturbation, and may result in further extinctions, so called secondary extinctions. The traits of the species initially lost, can be a potential predictor of the magnitude of secondary species loss. In Paper I of this thesis, I show that when making such predictions, it is important to incorporate temporally dynamic species interactions and abundances, in order not to underestimate the importance of certain species, such as top predators.

    I further show that species traits alone are not particularly good predictors of secondary extinction risk (Paper I), but that in combination with community level properties they are (Paper II). Indeed, there seems to be an interaction such that the specific property making a community prone to secondary species loss, depends on what kind of species was lost in the primary extinction. As different types of perturbation put different types of species at risk of (primary) extinction, this means that the specific property making a community prone to secondary species loss, will depend on the type of perturbation the community is subjected to.

    One of the predicted main drivers of future species extinction is climate change. If the local climate becomes adverse, a species can either migrate to new and better areas or stay and evolve. Both these processes will be important in determining the magnitude of species loss under climate change. However, migration and evolution do not occur in vacuum – the biotic community in which these processes play out may modulate their effect on biodiversity. In paper III, I show that the strength of competition between species modulates the effect of both dispersal and evolution on the magnitude of species loss under climate change. The three-way interaction between interspecific competition, evolution and dispersal, creates a complex pattern of biodiversity responses, in which both evolution and dispersal can either increase or decrease the magnitude of species loss. Thus, when species interactions are incorporated, it is clear that even though migration and evolution may alleviate the impact of climate change for some species, they may indirectly aggravate the situation for others.

    In Paper III, the aspect of climate change incorporated in the model is an increase in mean annual temperature. But climate change is also predicted to increase environmental variability. Paper IV shows that species-rich communities are more sensitive to high environmental variability than species-poor ones. The smaller population sizes in the species-rich communities increased the extinction risk connected to population fluctuations driven by the variable environment. Hence, systems such as tropical forests and coral reefs are predicted to be particularly sensitive to the increased variability that may follow with climate change.

    In Paper IV, primary extinctions of primary producers result in extinction cascades of consumer species, when they lose their prey. However, in reality a consumer species might be able to switch to another prey, and such flexibility has both been observed and suggested as a potential rescue mechanism. But what is beneficial for an individual predator in the short-term can become detrimental to the ecological community in the long-term. Paper V shows that consumer flexibility often led to consumers continuously overexploiting their new prey, in the worst case to the point of system collapse. Thus, the suggested rescue mechanism aggravated the effect of initial species loss, rather than ameliorating it.

    Overall, the research presented here, underscores the importance of including population dynamics and biotic interactions when studying the effects of perturbation on biodiversity. Many of the results are complex, hard to foresee or even counter-intuitive, arising from the indirect effects of the perturbation being translated through the living web of species interactions.

    List of papers
    1. Robustness to secondary extinctions: Comparing trait-based sequential deletions in static and dynamic food webs
    Open this publication in new window or tab >>Robustness to secondary extinctions: Comparing trait-based sequential deletions in static and dynamic food webs
    Show others...
    2011 (English)In: Basic and Applied Ecology, ISSN 1439-1791, E-ISSN 1618-0089, Vol. 12, no 7, 571-580 p.Article in journal (Refereed) Published
    Abstract [en]

    The loss of species from ecological communities can unleash a cascade of secondary extinctions, the risk and extent of which are likely to depend on the traits of the species that are lost from the community. To identify species traits that have the greatest impact on food web robustness to species loss we here subject allometrically scaled, dynamical food web models to several deletion sequences based on species’ connectivity, generality, vulnerability or body mass. Further, to evaluate the relative importance of dynamical to topological effects we compare robustness between dynamical and purely topological models. This comparison reveals that the topological approach overestimates robustness in general and for certain sequences in particular. Top-down directed sequences have no or very low impact on robustness in topological analyses, while the dynamical analysis reveals that they may be as important as high-impact bottom-up directed sequences. Moreover, there are no deletion sequences that result, on average, in no or very few secondary extinctions in the dynamical approach. Instead, the least detrimental sequence in the dynamical approach yields an average robustness similar to the most detrimental (non-basal) deletion sequence in the topological approach. Hence, a topological analysis may lead to erroneous conclusions concerning both the relative and the absolute importance of different species traits for robustness. The dynamical sequential deletion analysis shows that food webs are least robust to the loss of species that have many trophic links or that occupy low trophic levels. In contrast to previous studies we can infer, albeit indirectly, that secondary extinctions were triggered by both bottom-up and top-down cascades.

    Place, publisher, year, edition, pages
    Elsevier, 2011
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-73611 (URN)10.1016/j.baae.2011.09.008 (DOI)000299149700003 ()
    Note

    funding agencies|European Science Foundation||German Research Foundation| BR 2315/11-1 |

    Available from: 2012-01-10 Created: 2012-01-10 Last updated: 2017-04-19
    2. The interaction between species traits and community properties determine food web resistance to species loss
    Open this publication in new window or tab >>The interaction between species traits and community properties determine food web resistance to species loss
    2014 (English)Manuscript (preprint) (Other academic)
    Abstract [en]

    The ability to identify the ecosystems most vulnerable to species loss is fundamental for the allocation of conservation efforts. With this aim, the traits of keystone species have been investigated, as have the properties defining systems especially sensitive to species loss. However, these two have rarely been investigated in relation to each other. Here we show, that the traits of the species primarily lost act in conjunction with the properties of the food web from which it is lost, in determining the resistance of the system. We find that the extent of bottom-up extinction cascades is determined mainly by traits related to food web topology, while traits related to population dynamics govern the extent of top-down cascades. As different disturbances affect species with different traits, this interaction implies that the characteristics defining a sensitive community depend on the disturbance it is subjected to.

    Keyword
    Sequential deletion, species loss, perturbation, stability, robustness, secondary extinction cascades, top-predator loss, meso-predator release, body size, allometric relationships, functional response.
    National Category
    Other Biological Topics
    Identifiers
    urn:nbn:se:liu:diva-108903 (URN)
    Available from: 2014-07-11 Created: 2014-07-11 Last updated: 2014-07-11Bibliographically approved
    3. The strength of interspecific competition modulates the eco-evolutionary response to climate change
    Open this publication in new window or tab >>The strength of interspecific competition modulates the eco-evolutionary response to climate change
    Show others...
    2014 (English)Manuscript (preprint) (Other academic)
    Abstract [en]

    Climate change is predicted to have major implications for global biodiversity. Dispersal and evolution may become crucial for species survival, as species must either adapt or migrate to track the changing climate. However, migration and evolution do not occur in vacuum – the biotic community in which these processes play out may modulate their effect on biodiversity. Here, we use an eco-evolutionary, spatially explicit, multi-species model that allows us to examine the interactive effects of competition, adaptation and dispersal on species richness in plant communities under global warming. We find that there is a larger decline in global species richness when interspecific competition is strong. Furthermore, there is a three-way interaction between interspecific competition, evolution and dispersal that creates a complex pattern of biodiversity responses, in which both evolution and dispersal can either increase or decrease the magnitude of species loss. This interaction arises for at least two reasons: 1) different levels of dispersal, evolution and competition creates differences in local and global community structure before climate change, and 2) competitive interactions determine whether the benefits of dispersal and/or evolution (climate tracking and adaptation) outweighs the risks (competitive exclusion).

    Keyword
    Climate change, increased temperature, biodiversity loss, species extinctions, competition communities, dispersal, migration, invasion, evolution, local adaptation, tolerance curves
    National Category
    Other Biological Topics
    Identifiers
    urn:nbn:se:liu:diva-108904 (URN)
    Available from: 2014-07-11 Created: 2014-07-11 Last updated: 2014-07-11Bibliographically approved
    4. Species-rich ecosystems are vulnerable to cascading extinctions in an indreasingly variable world
    Open this publication in new window or tab >>Species-rich ecosystems are vulnerable to cascading extinctions in an indreasingly variable world
    Show others...
    2012 (English)In: Ecology and Evolution, ISSN 2045-7758, E-ISSN 2045-7758, Vol. 2, no 4, 858-874 p.Article in journal (Refereed) Published
    Abstract [en]

    Global warming leads to increased intensity and frequency of weather extremes. Such increased environmental variability might in turn result in increased variation in the demographic rates of interacting species with potentially important consequences for the dynamics of food-webs. Using a theoretical approach we here explore the response of food-webs to a highly variable environment. We investigate how species richness and correlation in the responses of species to environmental fluctuations affect the risk of extinction cascades. We find that the risk of extinction cascades increases with increasing species richness, especially when correlation among species is low. Initial extinctions of primary producer species unleash bottom-up extinction cascades, especially in webs with specialist consumers. In this sense, species-rich ecosystems are less robust to increasing levels of environmental variability than species-poor ones. Our study thus suggests that highly species-rich ecosystems like coral reefs and tropical rainforests might be particularly vulnerable to increased climate variability.

    Place, publisher, year, edition, pages
    John Wiley & Sons, 2012
    Keyword
    Biodiversity; climate change; environmental variability; ecological networks; extinction cascades; food-web; species interactions; stability; stochastic models; weather extremes
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-74700 (URN)10.1002/ece3.218 (DOI)000312444000015 ()
    Available from: 2012-02-05 Created: 2012-02-05 Last updated: 2017-04-19Bibliographically approved
    5. Adaptive rewiring aggravates the effects of species loss in ecosystems
    Open this publication in new window or tab >>Adaptive rewiring aggravates the effects of species loss in ecosystems
    2015 (English)In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 6, 8412Article in journal (Other academic) Published
    Abstract [en]

    Loss of one species in an ecosystem can trigger extinctions of other dependent species. For instance, specialist predators will go extinct following the loss of their only prey unless they can change their diet. It has therefore been suggested that an ability of consumers to rewire to novel prey should mitigate the consequences of species loss by reducing the risk of cascading extinction. Using a new modelling approach on natural and computer-generated food webs we find that, on the contrary, rewiring often aggravates the effects of species loss. This is because rewiring can lead to overexploitation of resources, which eventually causes extinction cascades. Such a scenario is particularly likely if prey species cannot escape predation when rare and if predators are efficient in exploiting novel prey. Indeed, rewiring is a two-edged sword; it might be advantageous for individual predators in the short term, yet harmful for long-term system persistence.

    Place, publisher, year, edition, pages
    Nature Publishing Group, 2015
    Keyword
    Resistance, extinction risk, secondary extinction cascades, environmental variation, stochastic, response diversity, functional responses
    National Category
    Biological Sciences
    Identifiers
    urn:nbn:se:liu:diva-108905 (URN)10.1038/ncomms9412 (DOI)000363138400004 ()
    Note

    Funding text: Linkoping University.

    The original titel of this article was Adaptive rewiring aggravates the effects of species loss in ecological networks.

    Available from: 2014-07-11 Created: 2014-07-11 Last updated: 2016-01-21Bibliographically approved
  • 27.
    Curtsdotter, Alva
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology. Linköping University, The Institute of Technology.
    Binzer, Amrei
    J.F. Blumenbach Institute of Zoology and Anthropology, Georg-August University, Göttingen, Germany.
    Brose, Ulrich
    J.F. Blumenbach Institute of Zoology and Anthropology, Georg-August University, Göttingen, Germany.
    de Castro, Fransisco
    Department of Ecology and Ecological Modelling, University of Potsdam, Germany.
    Ebenman, Bo
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology. Linköping University, The Institute of Technology.
    Eklöf, Anna
    Department of Ecology and Evolution, University of Chicago, United States.
    O. Riede, Jens
    J.F. Blumenbach Institute of Zoology and Anthropology, Georg-August University, Göttingen, Germany.
    Thierry, Aaron
    Department of Animal and Plant Sciences, University of Sheffield, United Kingdom. Microsoft Research, JJ Thompson Avenue, Cambridge, CB3 0FB, UK.
    Rall, Björn C.
    J.F. Blumenbach Institute of Zoology and Anthropology, Georg-August University, Göttingen, Germany.
    Robustness to secondary extinctions: Comparing trait-based sequential deletions in static and dynamic food webs2011In: Basic and Applied Ecology, ISSN 1439-1791, E-ISSN 1618-0089, Vol. 12, no 7, 571-580 p.Article in journal (Refereed)
    Abstract [en]

    The loss of species from ecological communities can unleash a cascade of secondary extinctions, the risk and extent of which are likely to depend on the traits of the species that are lost from the community. To identify species traits that have the greatest impact on food web robustness to species loss we here subject allometrically scaled, dynamical food web models to several deletion sequences based on species’ connectivity, generality, vulnerability or body mass. Further, to evaluate the relative importance of dynamical to topological effects we compare robustness between dynamical and purely topological models. This comparison reveals that the topological approach overestimates robustness in general and for certain sequences in particular. Top-down directed sequences have no or very low impact on robustness in topological analyses, while the dynamical analysis reveals that they may be as important as high-impact bottom-up directed sequences. Moreover, there are no deletion sequences that result, on average, in no or very few secondary extinctions in the dynamical approach. Instead, the least detrimental sequence in the dynamical approach yields an average robustness similar to the most detrimental (non-basal) deletion sequence in the topological approach. Hence, a topological analysis may lead to erroneous conclusions concerning both the relative and the absolute importance of different species traits for robustness. The dynamical sequential deletion analysis shows that food webs are least robust to the loss of species that have many trophic links or that occupy low trophic levels. In contrast to previous studies we can infer, albeit indirectly, that secondary extinctions were triggered by both bottom-up and top-down cascades.

  • 28.
    Curtsdotter, Alva
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology. Linköping University, The Institute of Technology.
    Binzer, Amrei
    J.F. Blumenbach Institute of Zoology and Anthropology, Georg-August University, Göttingen, Germany.
    Brose, Ulrich
    J.F. Blumenbach Institute of Zoology and Anthropology, Georg-August University, Göttingen, Germany.
    Ebenman, Bo
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology. Linköping University, The Institute of Technology.
    The interaction between species traits and community properties determine food web resistance to species loss2014Manuscript (preprint) (Other academic)
    Abstract [en]

    The ability to identify the ecosystems most vulnerable to species loss is fundamental for the allocation of conservation efforts. With this aim, the traits of keystone species have been investigated, as have the properties defining systems especially sensitive to species loss. However, these two have rarely been investigated in relation to each other. Here we show, that the traits of the species primarily lost act in conjunction with the properties of the food web from which it is lost, in determining the resistance of the system. We find that the extent of bottom-up extinction cascades is determined mainly by traits related to food web topology, while traits related to population dynamics govern the extent of top-down cascades. As different disturbances affect species with different traits, this interaction implies that the characteristics defining a sensitive community depend on the disturbance it is subjected to.

  • 29.
    Curtsdotter, Alva
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology. Linköping University, The Institute of Technology.
    Münger, Peter
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Norberg, Jon
    Department of Systems Ecology, Stockholm University/Stockholm Resilience Centre, Stockholm University, Sweden.
    Åkesson, Anna
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Ebenman, Bo
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology. Linköping University, The Institute of Technology.
    The strength of interspecific competition modulates the eco-evolutionary response to climate change2014Manuscript (preprint) (Other academic)
    Abstract [en]

    Climate change is predicted to have major implications for global biodiversity. Dispersal and evolution may become crucial for species survival, as species must either adapt or migrate to track the changing climate. However, migration and evolution do not occur in vacuum – the biotic community in which these processes play out may modulate their effect on biodiversity. Here, we use an eco-evolutionary, spatially explicit, multi-species model that allows us to examine the interactive effects of competition, adaptation and dispersal on species richness in plant communities under global warming. We find that there is a larger decline in global species richness when interspecific competition is strong. Furthermore, there is a three-way interaction between interspecific competition, evolution and dispersal that creates a complex pattern of biodiversity responses, in which both evolution and dispersal can either increase or decrease the magnitude of species loss. This interaction arises for at least two reasons: 1) different levels of dispersal, evolution and competition creates differences in local and global community structure before climate change, and 2) competitive interactions determine whether the benefits of dispersal and/or evolution (climate tracking and adaptation) outweighs the risks (competitive exclusion).

  • 30.
    Dee, Laura E.
    et al.
    University of Minnesota Twin Cities, MN 55108 USA; University of Minnesota Twin Cities, MN 55108 USA.
    Allesina, Stefano
    University of Chicago, IL 60637 USA; University of Chicago, IL 60637 USA.
    Bonn, Aletta
    UFZ Helmholtz Centre Environm Research, Germany; Friedrich Schiller University of Jena, Germany; Gerrnan Centre Integrat Biodivers Research iDiv, Germany.
    Eklöf, Anna
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology. Linköping University, Faculty of Science & Engineering.
    Gaines, Steven D.
    University of Calif Santa Barbara, CA 93117 USA.
    Hines, Jes
    Gerrnan Centre Integrat Biodivers Research iDiv, Germany; University of Leipzig, Germany.
    Jacob, Ute
    Gerrnan Centre Integrat Biodivers Research iDiv, Germany; University of Goettingen, Germany.
    McDonald-Madden, Eve
    University of Queensland, Australia.
    Possingham, Hugh
    University of Queensland, Australia.
    Schroeter, Matthias
    UFZ Helmholtz Centre Environm Research, Germany; Gerrnan Centre Integrat Biodivers Research iDiv, Germany.
    Thompson, Ross M.
    University of Canberra, Australia.
    Operationalizing Network Theory for Ecosystem Service Assessments2017In: Trends in Ecology & Evolution, ISSN 0169-5347, E-ISSN 1872-8383, Vol. 32, no 2, 118-130 p.Article, review/survey (Refereed)
    Abstract [en]

    Managing ecosystems to provide ecosystem services in the face of global change is a pressing challenge for policy and science. Predicting how alternative management actions and changing future conditions will alter services is complicated by interactions among components in ecological and socioeconomic systems. Failure to understand those interactions can lead to detrimental outcomes from management decisions. Network theory that integrates ecological and socioeconomic systems may provide a path to meeting this challenge. While network theory offers promising approaches to examine ecosystem services, few studies have identified how to operationalize networks for managing and assessing diverse ecosystem services. We propose a framework for how to use networks to assess how drivers and management actions will directly and indirectly alter ecosystem services.

  • 31.
    Digel, Christoph
    et al.
    University of Gottingen, Germany.
    Curtsdotter, Alva
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology. Linköping University, The Institute of Technology.
    Riede, Jens
    Deutsch Wetterdienst, Germany.
    Klarner, Bernhard
    University of Gottingen, Germany.
    Brose, Ulrich
    University of Gottingen, Germany.
    Unravelling the complex structure of forest soil food webs: higher omnivory and more trophic levels2014In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 123, no 10, 1157-1172 p.Article in journal (Refereed)
    Abstract [en]

    Food web topologies depict the community structure as distributions of feeding interactions across populations. Although the soil ecosystem provides important functions for aboveground ecosystems, data on complex soil food webs is notoriously scarce, most likely due to the difficulty of sampling and characterizing the system. To fill this gap we assembled the complex food webs of 48 forest soil communities. The food webs comprise 89 to 168 taxa and 729 to 3344 feeding interactions. The feeding links were established by combining several molecular methods (stable isotope, fatty acid and molecular gut content analyses) with feeding trials and literature data. First, we addressed whether soil food webs (n = 48) differ significantly from those of other ecosystem types (aquatic and terrestrial aboveground, n = 77) by comparing 22 food web parameters. We found that our soil food webs are characterized by many omnivorous and cannibalistic species, more trophic chains and intraguild-predation motifs than other food webs and high average and maximum trophic levels. Despite this, we also found that soil food webs have a similar connectance as other ecosystems, but interestingly a higher link density and clustering coefficient. These differences in network structure to other ecosystem types may be a result of ecosystem specific constraints on hunting and feeding characteristics of the species that emerge as network parameters at the food-web level. In a second analysis of land-use effects, we found significant but only small differences of soil food web structure between different beech and coniferous forest types, which may be explained by generally strong selection effects of the soil that are independent of human land use. Overall, our study has unravelled some systematic structures of soil food-webs, which extends our mechanistic understanding how environmental characteristics of the soil ecosystem determine patterns at the community level.

  • 32.
    Ebeman, Bo
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology. Linköping University, The Institute of Technology.
    Lennart, PerssonUmeå universitet.
    Size-structured populations: ecology and evolution1988Collection (editor) (Other academic)
  • 33.
    Ebenman, Bo
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology. Linköping University, The Institute of Technology.
    Dynamics of age- and size-structured populations: intraspecific competition1988In: Size-structured populations: ecology and evolution / [ed] Bo Ebenman, Lennart Persson, Berlin: Springer Berlin/Heidelberg, 1988, 127-139 p.Chapter in book (Other academic)
  • 34.
    Ebenman, Bo
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology. Linköping University, The Institute of Technology.
    Response of ecosystems to realistic extinction sequences2011In: Journal of Animal Ecology, ISSN 0021-8790, E-ISSN 1365-2656, Vol. 80, no 2, 307-309 p.Article in journal (Other academic)
    Abstract [en]

    Recent research suggests that effects of species loss on the structure and functioning of ecosystems willcritically depend on the order with which species go extinct. However, there are few studies of theresponse of natural ecosystems to realistic extinction sequences. Using an extinction scenario basedon the International Union for Conservation of Nature (IUCN) Red List, de Visser et al. sequentiallydeleted species from a topological model of the Serengeti food web. Under this scenario, large-bodiedspecies like top predators and mega-herbivores go extinct first. The resulting changes in the trophicstructure of the food web might affect the robustness of the ecosystem to future disturbances.

  • 35.
    Ebenman, Bo
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology .
    Jonsson, Tomas
    Systems biology group Skövde University.
    Using community viability analysis to identify fragile systems and keystone species2005In: Trends in Ecology & Evolution, ISSN 0169-5347, Vol. 20, no 10, 568-575 p.Article in journal (Refereed)
    Abstract [en]

    Owing to interdependences among species in ecological communities, the loss of one species can trigger a cascade of secondary extinctions with potentially dramatic effects on the functioning and stability of the community. It is, therefore, important to assess the risk and likely extent of secondary extinctions. Community viability analysis is a new technique that can be used to accomplish this goal. The analysis can also be used to identify fragile community structures and keystone species and, hence, to provide guidelines for conservation priorities. Here, we describe the principles underlying community viability analysis and review its contributions to our understanding of the response of ecological communities to species loss.

  • 36.
    Ebenman, Bo
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology . Linköping University, The Institute of Technology.
    Law, Richard
    2Biology Department, University of York, York, United Kingdom.
    Borrvall, Charlotte
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology . Linköping University, The Institute of Technology.
    Community viability analysis: the response of ecological communities to species loss.2004In: Ecology, ISSN 0012-9658, Vol. 85, no 9, 2591-2600 p.Article in journal (Refereed)
    Abstract [en]

    The loss of a species from an ecological community can set up a cascade of secondary extinctions that in the worst case could lead to the collapse of the community. Both deterministic and stochastic mechanisms may be involved in such secondary extinctions. To investigate the extent of secondary extinctions in ecological communities following the loss of a species, we here develop a community viability analysis. We introduce a measure called the “quasi-collapse risk” that is defined as the probability that the number of species in a community falls below some defined value within a fixed period of time following the loss of a species. We develop deterministic and stochastic methods for finding post-extinction communities. We use these methods to investigate the relationship between diversity (species richness) and quasi-collapse risks in model communities. It is shown that, in a deterministic context, communities with more species within trophic levels have a larger fraction of species remaining in post-extinction communities. This benefit of species richness is to a large extent lost in the presence of demographic stochasticity. The reason for this is a negative relationship between population density and species diversity. We also show that communities become increasingly triangular in shape as secondary extinctions take place, due to greater extinction risk of species at higher trophic levels. We argue that this new approach holds some promise for identifying fragile ecosystems and keystone species.

  • 37.
    Edstam, Monika M.
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Biology. Linköping University, The Institute of Technology.
    Blomqvist, Kristina
    Linköping University, Department of Physics, Chemistry and Biology, Biology. Linköping University, The Institute of Technology.
    Eklöf, Anna
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology. Linköping University, The Institute of Technology.
    Wennergren, Uno
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology. Linköping University, The Institute of Technology.
    Edqvist, Johan
    Linköping University, Department of Physics, Chemistry and Biology, Biology. Linköping University, The Institute of Technology.
    Coexpression patterns indicate that GPI-anchored non-specific lipid transfer proteins are involved in accumulation of cuticular wax, suberin and sporopollenin2013In: Plant Molecular Biology, ISSN 0167-4412, E-ISSN 1573-5028, Vol. 83, no 6, 625-649 p.Article in journal (Refereed)
    Abstract [en]

    The non-specific lipid transfer proteins (nsLTP) are unique to land plants. The nsLTPs are characterized by a compact structure with a central hydrophobic cavity and can be classified to different types based on sequence similarity, intron position or spacing between the cysteine residues. The type G nsLTPs (LTPGs) have a GPI-anchor in the C-terminal region which attaches the protein to the exterior side of the plasma membrane. The function of these proteins, which are encoded by large gene families, has not been systematically investigated so far. In this study we have explored microarray data to investigate the expression pattern of the LTPGs in Arabidopsis and rice. We identified that the LTPG genes in each plant can be arranged in three expression modules with significant coexpression within the modules. According to expression patterns and module sizes, the Arabidopsis module AtI is functionally equivalent to the rice module OsI, AtII corresponds to OsII and AtIII is functionally comparable to OsIII. Starting from modules AtI, AtII and AtIII we generated extended networks with Arabidopsis genes coexpressed with the modules. Gene ontology analyses of the obtained networks suggest roles for LTPGs in the synthesis or deposition of cuticular waxes, suberin and sporopollenin. The AtI-module is primarily involved with cuticular wax, the AtII-module with suberin and the AtIII-module with sporopollenin. Further transcript analysis revealed that several transcript forms exist for several of the LTPG genes in both Arabidopsis and rice. The data suggests that the GPI-anchor attachment and localization of LTPGs may be controlled to some extent by alternative splicing.

  • 38.
    Eklöf, Anna
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology . Linköping University, The Institute of Technology.
    Species extinctions in food webs: local and regional processes2009Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Loss of biodiversity is one of the most severe threats to the ecosystems of the world. The major causes behind the high population and species extinction rates are anthropogenic activities such as overharvesting of natural populations, pollution, climate change and destruction and fragmentation of natural habitats. There is an urgent need of understanding how these species losses affect the ecological structure and functioning of our ecosystems. Ecological communities exist in a landscape but the spatial aspects of community dynamics have until recently to large extent been ignored. However, the community’s response to species losses is likely to depend on both the structure of the local community as well as its interactions with surrounding communities. Also the characteristics of the species going extinct do affect how the community can cope with species loss. The overall goal of the present work has been to investigate how both local and regional processes affect ecosystem stability, in the context of preserved biodiversity and maintained ecosystem functioning. The focus is particularly on how these processes effects ecosystem’s response to species loss. To accomplish this goal I have formulated and analyzed mathematical models of ecological communities. We start by analyzing the local processes (Paper I and II) and continue by adding the regional processes (Paper III, IV and V).

    In Paper I we analyze dynamical models of ecological communities of different complexity (connectance) to investigate how the structure of the communities affects their resistance to species loss. We also investigate how the resistance is affected by the characteristics, like trophic level and connectivity, of the initially lost species. We find that complex communities are more resistant to species loss than simple communities. The loss of species at low trophic levels and/or with high connectivity (many links to other species) triggers, on average, the highest number of secondary extinctions. We also investigate the structure of the post-extinction community. Moreover, we compare our dynamical analysis with results from topological analysis to evaluate the importance of incorporating dynamics when assessing the risk and extent of cascading extinctions.

    The characteristics of a species, like its trophic position and connectivity (number of ingoing and outgoing trophic links) will affect the consequences of its loss as well as its own vulnerability to secondary extinction. In Paper II we characterize the species according to their trophic/ecological uniqueness, a new measure of species characteristic we develop in this paper. A species that has no prey or predators in common with any other species in the community will have a high tropic uniqueness. Here we examine the effect of secondary extinctions on an ecological community’s trophic diversity, the range of different trophic roles played by the species in a community. We find that secondary extinctions cause loss of trophic diversity greater than expected from chance. This occurs because more tropically unique species are more vulnerable to secondary extinctions.

    In Paper III, IV and V we expand the analysis to also include the spatial dimension. Paper III is a book chapter discussing spatial aspects of food webs. In Paper IV we analyze how metacommunities (a set of local communities in the landscape connected by species dispersal) respond to species loss and how this response is affected by the structure of the local communities and the number of patches in the metacommunity. We find that the inclusion of space reduces the risk of global and local extinctions and that lowly connected communities are more sensitive to species loss.

    In Paper V we investigate how the trophic structure of the local communities, the spatial structure of the landscape and the dispersal patterns of species affect the risk of local extinctions in the metacommunity. We find that the pattern of dispersal can have large effects on local diversity. Dispersal rate as well as dispersal distance are important: low dispersal rates and localized dispersal decrease the risk of local and global extinctions while high dispersal rates and global dispersal increase the risk. We also show that the structure of the local communities plays a significant role for the effects of dispersal on the dynamics of the metacommunity. The species that are most affected by the introduction of the spatial dimension are the top predators.

    List of papers
    1. Species loss and secondary extinctions in simple and complex model communities
    Open this publication in new window or tab >>Species loss and secondary extinctions in simple and complex model communities
    2006 (English)In: Journal of Animal Ecology, ISSN 0021-8790, E-ISSN 1365-2656, Vol. 75, no 1, 239-246 p.Article in journal (Refereed) Published
    Abstract [en]
    1. The loss of a species from an ecological community can trigger a cascade of secondary extinctions. Here we investigate how the complexity (connectance) of model communities affects their response to species loss. Using dynamic analysis based on a global criterion of persistence (permanence) and topological analysis we investigate the extent of secondary extinctions following the loss of different kinds of species.
    2. We show that complex communities are, on average, more resistant to species loss than simple communities: the number of secondary extinctions decreases with increasing connectance. However, complex communities are more vulnerable to loss of top predators than simple communities.
    3. The loss of highly connected species (species with many links to other species) and species at low trophic levels triggers, on average, the largest number of secondary extinctions. The effect of the connectivity of a species is strongest in webs with low connectance.
    4. Most secondary extinctions are due to direct bottom-up effects: consumers go extinct when their resources are lost. Secondary extinctions due to trophic cascades and disruption of predator-mediated coexistence also occur. Secondary extinctions due to disruption of predator-mediated coexistence are more common in complex communities than in simple communities, while bottom-up and top-down extinction cascades are more common in simple communities.
    5. Topological analysis of the response of communities to species loss always predicts a lower number of secondary extinctions than dynamic analysis, especially in food webs with high connectance.
    Place, publisher, year, edition, pages
    Wiley InterScience, 2006
    Keyword
    Cascading extinction, connectance, food web, keystone species, resistance
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-37000 (URN)10.1111/j.1365-2656.2006.01041.x (DOI)000235043700024 ()33326 (Local ID)33326 (Archive number)33326 (OAI)
    Available from: 2009-10-10 Created: 2009-10-10 Last updated: 2017-04-18Bibliographically approved
    2. Trophically Unique Species Are Vulnerable to Cascading Extinction
    Open this publication in new window or tab >>Trophically Unique Species Are Vulnerable to Cascading Extinction
    2008 (English)In: American Naturalist, ISSN 0003-0147, E-ISSN 1537-5323, Vol. 171, no 5, 568-579 p.Article in journal (Refereed) Published
    Abstract [en]

    Understanding which species might become extinct and the consequences of such loss is critical. One consequence is a cascade of further, secondary extinctions. While a significant amount is known about the types of communities and species that suffer secondary extinctions, little is known about the consequences of secondary extinctions for biodiversity. Here we examine the effect of these secondary extinctions on trophic diversity, the range of trophic roles played by the species in a community. Our analyses of natural and model food webs show that secondary extinctions cause loss of trophic diversity greater than that expected from chance, a result that is robust to variation in food web structure, distribution of interactions strengths, functional response, and adaptive foraging. Greater than expected loss of trophic diversity occurs because more trophically unique species are more vulnerable to secondary extinction. This is not a straightforward consequence of these species having few links with others but is a complex function of how direct and indirect interactions affect species persistence. A positive correlation between a species’ extinction probability and the importance of its loss defines high-risk species and should make their conservation a priority.

    Place, publisher, year, edition, pages
    University of Chicago Press, 2008
    Keyword
    biodiversity, redundancy, stability, food webs, species deletions
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-11923 (URN)10.1086/587068 (DOI)000255212900004 ()
    Note

    Original publication: Owen L. Petchey, Anna Eklöf, Charlotte Borrvall and Bo Ebenman, Trophically Unique Species Are Vulnerable to Cascading Extinction, 2008, American Naturalist, (171), 5, 568-579. http://dx.doi.org/10.1086/587068. Copyright © 2008. University of Chicago Press. All rights reserved

    Available from: 2008-05-28 Created: 2008-05-28 Last updated: 2017-04-19Bibliographically approved
    3. Spatial aspects of food webs
    Open this publication in new window or tab >>Spatial aspects of food webs
    Show others...
    2005 (English)In: Dynamic Food Webs: Multispecies Assemblages, Ecosystem Development and Environmental Change / [ed] P.C. deRuiter, V. Wolters & J.C. Moore, London, UK: Elsevier, 2005, Vol. 3, 463-469 p.Conference paper, Published paper (Refereed)
    Abstract [en]

    Aspects of spatial scale have until recently been largely ignored in empirical and theoretical food web studies (e.g., Cohen & Briand 1984, Martinez 1992, but see Bengtsson et al. 2002, Bengtsson & Berg, this book). Most ecologists tend to conceptualize and represent food webs as static representations of communities, depicting a community assemblage as sampled at a particular point in time, or highly aggregated trophic group composites over broader scales of time and space (Polis et al. 1996). Moreover, most researchers depict potential food webs, which contain all species sampled and all potential trophic links based on literature reviews, several sampling events, or laboratory feeding trials. In reality, however, not all these potential feeding links are realized as not all species co-occur, and not all samples in space or time can contain all species (Schoenly & Cohen 1991), hence, yielding a variance of food web architecture in space (Brose et al. 2004). In recent years, food web ecologists have recognized that food webs are open systems – that are influence by processes in adjacent systems – and spatially heterogeneous (Polis et al. 1996). This influence of adjacent systems can be bottom-up, due to allochthonous inputs of resources (Polis & Strong 1996, Huxel & McCann 1998, Mulder & De Zwart 2003), or top-down due to the regular or irregular presence of top predators (e.g., Post et al. 2000, Scheu 2001). However, without a clear understanding of the size of a system and a definition of its boundaries it is not possible to judge if flows are internal or driven by adjacent systems. Similarly, the importance of allochthony is only assessable when the balance of inputs and outputs are known relative to the scale and throughputs within the system itself. At the largest scale of the food web – the home range of a predator such as wolf, lion, shark or eagle of roughly 50 km2 to 300 km2 –the balance of inputs and outputs caused by wind and movement of water may be small compared to the total trophic flows within the home range of the large predator (Cousins 1990). Acknowledging these issues of space, Polis et al (1996) argued that progress toward the next phase of food web studies would require addressing spatial and temporal processes. Here, we present a conceptual framework with some nuclei about the role of space in food web ecology. Although we primarily address spatial aspects, this framework is linked to a more general concept of spatio-temporal scales of ecological research.

    Place, publisher, year, edition, pages
    London, UK: Elsevier, 2005
    Series
    Theoretical Ecology Series, ISSN 1875-306X
    National Category
    Ecology
    Identifiers
    urn:nbn:se:liu:diva-31067 (URN)16789 (Local ID)9780120884582 (ISBN)0120884585 (ISBN)16789 (Archive number)16789 (OAI)
    Conference
    Food Web Symposium 2003, Giessen, Germany, 13-16 November 2003
    Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2015-09-14Bibliographically approved
    4. Cascading extinctions in spatially coupled food webs
    Open this publication in new window or tab >>Cascading extinctions in spatially coupled food webs
    (English)Manuscript (preprint) (Other academic)
    Abstract [en]

    The spatial structure of ecological communities as well as the dynamics and structure of local communities can be expected to have important consequences for the long-term persistence of metacommunities, that is, their resistance to different kind of perturbations. The aim of the present work is to investigate how web connectance of local communities and number of local habitat patches affects a metacommunity’s response to the global loss of a species. We find that the inclusion of space significantly reduces the risk of global and local cascading extinctions. It is shown that communities with sparsely connected food webs are the most sensitive to species loss, but also that they are particularly well stabilized by the introduction of space. In agreement with theoretical studies of non-spatial habitats, species at the highest trophic level are the most vulnerable to secondary extinction, although they often take the longest time to die out. This is particularly pronounced in spatial habitats, where the top predators appear to be the least well adapted to exploit the stabilizing properties of space.

    Keyword
    Cascading extinction, dispersal, food web connectance, habitat destruction, metacommunity, spatial structure, species interactions, species loss
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-51955 (URN)
    Available from: 2009-11-24 Created: 2009-11-24 Last updated: 2009-11-24Bibliographically approved
    5. Effects of dispersal on local extinctions in multi-trophic metacommunities
    Open this publication in new window or tab >>Effects of dispersal on local extinctions in multi-trophic metacommunities
    (English)Manuscript (preprint) (Other academic)
    Abstract [en]

    As a result of habitat destruction many ecological communities have a fragmented distribution and are built up of partially isolated local communities connected through dispersal of interacting species. The dynamics of such metacommunities is governed both by local processes (interactions among species coexisting within habitat patches) and regional processes (movement of species among habitat patches). Earlier theoretical work on simple metacommunities have mainly focused on the positive effects of space and dispersal for the coexistence of interacting species and hence for local and regional species diversity. However, it is plausible that dispersal might also pose some kind of risk to the dispersing individuals. Here we explore how such risks might affect the dynamics of metacommunities. We develop spatially and dynamically explicit models to investigate how the trophic structure (connectance) of local communities, the spatial structure of the metacommunity and the dispersal characteristics of species affect species extinction risks. Species extinction risks in these open communities are measured relative to the extinction risks in closed communities (i.e. no dispersal). We show that the introduction of dispersal among initially closed local communities might lead to increased probability of local species extinction. The effects of dispersal depend on migration rate, movement pattern of individuals and the density of patches in the landscape. Specifically, when dispersal involves a risk, high migration rates, global dispersal and low patch density will all lead to increased probability of local species extinctions. Furthermore, the trophic structure of local communities plays a significant role in the response of metacommunities to changes in the regional processes.

    Keyword
    Dispersal, dispersal risk, extinction, food web connectance, metacommunity, migration rate, spatial structure
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-51956 (URN)
    Available from: 2009-11-24 Created: 2009-11-24 Last updated: 2009-11-24Bibliographically approved
  • 39.
    Eklöf, Anna
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology.
    Ebenman, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology.
    Species loss and secondary extinctions in simple and complex model communities2006In: Journal of Animal Ecology, ISSN 0021-8790, E-ISSN 1365-2656, Vol. 75, no 1, 239-246 p.Article in journal (Refereed)
    Abstract [en]
    1. The loss of a species from an ecological community can trigger a cascade of secondary extinctions. Here we investigate how the complexity (connectance) of model communities affects their response to species loss. Using dynamic analysis based on a global criterion of persistence (permanence) and topological analysis we investigate the extent of secondary extinctions following the loss of different kinds of species.
    2. We show that complex communities are, on average, more resistant to species loss than simple communities: the number of secondary extinctions decreases with increasing connectance. However, complex communities are more vulnerable to loss of top predators than simple communities.
    3. The loss of highly connected species (species with many links to other species) and species at low trophic levels triggers, on average, the largest number of secondary extinctions. The effect of the connectivity of a species is strongest in webs with low connectance.
    4. Most secondary extinctions are due to direct bottom-up effects: consumers go extinct when their resources are lost. Secondary extinctions due to trophic cascades and disruption of predator-mediated coexistence also occur. Secondary extinctions due to disruption of predator-mediated coexistence are more common in complex communities than in simple communities, while bottom-up and top-down extinction cascades are more common in simple communities.
    5. Topological analysis of the response of communities to species loss always predicts a lower number of secondary extinctions than dynamic analysis, especially in food webs with high connectance.
  • 40.
    Eklöf, Anna
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology. Linköping University, The Institute of Technology.
    Kaneryd, Linda
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology. Linköping University, The Institute of Technology.
    Münger, Peter
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Climate change in metacommunities: dispersal gives double-sided effects on persistence2012In: Philosphical Transactions of the Royal Society B, ISSN 1471-2970, Vol. 367, no 1605, 2945-2954 p.Article in journal (Refereed)
    Abstract [en]

    Climate change is increasingly affecting the structure and dynamics of ecological communities bothat local and at regional scales, and this can be expected to have important consequences for theirrobustness and long-term persistence. The aim of the present work is to analyse how the spatialstructure of the landscape and dispersal patterns of species (dispersal rate and average dispersal distance)affects metacommunity response to two disturbances: (i) increased mortality during dispersaland (ii) local species extinction. We analyse the disturbances both in isolation and in combination.Using a spatially and dynamically explicit metacommunity model, we find that the effect of dispersalon metacommunity persistence is two-sided: on the one hand, high dispersal significantly reducesthe risk of bottom-up extinction cascades following the local removal of a species; on the otherhand, when dispersal imposes a risk to the dispersing individuals, high dispersal increases extinctionrisks, especially when dispersal is global. Large-bodied species with long generation times at thehighest trophic level are particularly vulnerable to extinction when dispersal involves a risk. Thissuggests that decreasing the mortality risk of dispersing individuals by improving the quality ofthe habitat matrix may greatly increase the robustness of metacommunities.

  • 41.
    Eklöf, Anna
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology . Linköping University, The Institute of Technology.
    Münger, Peter
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics . Linköping University, The Institute of Technology.
    Ebenman, Bo
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology . Linköping University, The Institute of Technology.
    Effects of dispersal on local extinctions in multi-trophic metacommunitiesManuscript (preprint) (Other academic)
    Abstract [en]

    As a result of habitat destruction many ecological communities have a fragmented distribution and are built up of partially isolated local communities connected through dispersal of interacting species. The dynamics of such metacommunities is governed both by local processes (interactions among species coexisting within habitat patches) and regional processes (movement of species among habitat patches). Earlier theoretical work on simple metacommunities have mainly focused on the positive effects of space and dispersal for the coexistence of interacting species and hence for local and regional species diversity. However, it is plausible that dispersal might also pose some kind of risk to the dispersing individuals. Here we explore how such risks might affect the dynamics of metacommunities. We develop spatially and dynamically explicit models to investigate how the trophic structure (connectance) of local communities, the spatial structure of the metacommunity and the dispersal characteristics of species affect species extinction risks. Species extinction risks in these open communities are measured relative to the extinction risks in closed communities (i.e. no dispersal). We show that the introduction of dispersal among initially closed local communities might lead to increased probability of local species extinction. The effects of dispersal depend on migration rate, movement pattern of individuals and the density of patches in the landscape. Specifically, when dispersal involves a risk, high migration rates, global dispersal and low patch density will all lead to increased probability of local species extinctions. Furthermore, the trophic structure of local communities plays a significant role in the response of metacommunities to changes in the regional processes.

  • 42.
    Eklöf, Anna
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology. Linköping University, The Institute of Technology.
    Münger, Peter
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Kaneryd, Linda
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology. Linköping University, The Institute of Technology.
    Ebenman, Bo
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology. Linköping University, The Institute of Technology.
    Can dispersal rescue metacommunities from extinction cascades?Manuscript (preprint) (Other academic)
    Abstract [en]

    Climate change and habitat loss are increasingly affecting the structure and dynamics of ecological communities both at the local and regional scale. Changes in the spatial structure of landscapes as well as in the trophic structure of local communities can be expected to have important consequences for the long-term persistence of species in metacommunities. The aim of the present work is to investigate how the spatial structure of the landscape (patch density) and dispersal patterns of species (migration rate and dispersal distance) affect a metacommunities response to local loss of species and to increased mortality of individuals during dispersal. Using a spatially and dynamically explicit metacommunity model we find that the effect of dispersal on metacommunity persistence is two-sided: on the one hand, when dispersal involves no risk, high migration rate significantly reduces the risk of bottom-up extinction cascades following the local removal of a species. The explanation for this is that recolonization rates of the locally removed species increases with increasing migration rate. On the other hand, when dispersal imposes a risk to the dispersing individuals, high migration rate increases extinction risks, especially when dispersal is global (long dispersal distances). Largebodied species with long generation times at the highest trophic level are particularly vulnerable to extinction when dispersal involves a risk. These results suggest that decreasing the mortality risk of dispersing individuals by improving the quality of the habitat matrix might greatly increase the robustness of metacommunities to local loss of species by enhancing recolonizations and rescue effects.

  • 43.
    Eklöf, Anna
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology . Linköping University, The Institute of Technology.
    Platts, Philip
    Ebenman, Bo
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology . Linköping University, The Institute of Technology.
    Cascading extinctions in spatially coupled food websManuscript (preprint) (Other academic)
    Abstract [en]

    The spatial structure of ecological communities as well as the dynamics and structure of local communities can be expected to have important consequences for the long-term persistence of metacommunities, that is, their resistance to different kind of perturbations. The aim of the present work is to investigate how web connectance of local communities and number of local habitat patches affects a metacommunity’s response to the global loss of a species. We find that the inclusion of space significantly reduces the risk of global and local cascading extinctions. It is shown that communities with sparsely connected food webs are the most sensitive to species loss, but also that they are particularly well stabilized by the introduction of space. In agreement with theoretical studies of non-spatial habitats, species at the highest trophic level are the most vulnerable to secondary extinction, although they often take the longest time to die out. This is particularly pronounced in spatial habitats, where the top predators appear to be the least well adapted to exploit the stabilizing properties of space.

  • 44.
    Eklöf, Anna
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology. Linköping University, Faculty of Science & Engineering.
    Stouffer, Daniel B.
    Centre for Integrative Ecology, School of Biological Sciences, University of Canterbury, Christchurch 8140, New Zealan.
    The phylogenetic component of food web structure and intervality2016In: Theoretical Ecology, ISSN 1874-1738, E-ISSN 1874-1746, Vol. 9, no 1, 107-115 p.Article in journal (Refereed)
    Abstract [en]

    Despite the exceptional complexity formed byspecies and their interactions in ecological networks, such asfood webs, regularities in the network structures are repeat-edly demonstrated. The interactions are determined by thecharacteristics of a species. The characteristics are in turndetermined by the species’ phylogenetic relationships, butalso by factors not related to evolutionary history. Here, wetest whether species’ phylogenetic relationships provides asignificant proxy for food web intervality. We thereafterquantify the degree to which different species traits remainvaluable predictors of food web structure after the base-line effect of species’ relatedness has been removed. Wefind that the phylogenetic relationships provide a significantbackground from which to estimate food web intervalityand thereby structure. However, we also find that thereis an important, non-negligible part of some traits, e.g.,body size, in food webs that is not accounted for by thephylogenetic relationships. Additionally, both these rela-tionships differ depending if a predator or a prey perspectiveis adopted. Clearly, species’ evolutionary history as well astraits not determined by phylogenetic relationships shapes predator-prey interactions in food webs, and the underly-ing evolutionary processes take place on slightly differenttime scales depending on the direction of predator-preyadaptations.

  • 45.
    Frossling, Jenny
    et al.
    SVA, Sweden Swedish University of Agriculture Science, Sweden .
    Ohlson, Anna
    SVA, Sweden Swedish University of Agriculture Science, Sweden .
    Bjorkman, Camilla
    Swedish University of Agriculture Science, Sweden .
    Håkansson, Nina
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology. Linköping University, The Institute of Technology.
    Noremark, Maria
    SVA, Sweden .
    Application of network analysis parameters in risk-based surveillance - Examples based on cattle trade data and bovine infections in Sweden2012In: Preventive Veterinary Medicine, ISSN 0167-5877, E-ISSN 1873-1716, Vol. 105, no 3, 202-208 p.Article in journal (Refereed)
    Abstract [en]

    Financial resources may limit the number of samples that can be collected and analysed in disease surveillance programmes. When the aim of surveillance is disease detection and identification of case herds, a risk-based approach can increase the sensitivity of the surveillance system. In this paper, the association between two network analysis measures, i.e. in-degree and ingoing infection chain, and signs of infection is investigated. It is shown that based on regression analysis of combined data from a recent cross-sectional study for endemic viral infections and network analysis of animal movements, a positive serological result for bovine coronavirus (BCV) and bovine respiratory syncytial virus (BRSV) is significantly associated with the purchase of animals. For BCV, this association was significant also when accounting for herd size and regional cattle density, but not for BRSV. Examples are given for different approaches to include cattle movement data in risk-based surveillance by selecting herds based on network analysis measures. Results show that compared to completely random sampling these approaches increase the number of detected positives, both for BCV and BRSV in our study population. It is concluded that network measures for the relevant time period based on updated databases of animal movements can provide a simple and straight forward tool for risk-based sampling.

  • 46.
    Gilljam, David
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology. Linköping University, Faculty of Science & Engineering.
    Structure and Stability of Ecological Networks: The role of dynamic dimensionality and species variability in resource use2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The main focus of this thesis is on the response of ecological communities to environmental variability and species loss. My approach is theoretical; I use mathematical models of networks where species population dynamics are described by ordinary differential equations. A common theme of the papers in my thesis is variation – variable link structure (Paper I) and within-species variation in resource use (Paper III and IV). To explore how such variation affect the stability of ecological communities in variable environments, I use numerical methods evaluating for example community persistence (the proportion of species surviving over time; Paper I, II and IV). I also develop a new method for quantifying the dynamical dimensionality of an ecological community and investigate its effect on community persistence in stochastic environments (Paper II). Moreover, if we are to gain trustworthy model output, it is of course of major importance to create study systems that reflect the structures of natural systems. To this end, I also study highly resolved, individual based empirical food web data sets (Paper III, IV).

    In Paper I, the effects of adaptive rewiring induced by resource loss on the persistence of ecological networks is investigated. Loss of one species in an ecosystem can trigger extinctions of other dependent species. For instance, specialist predators will go extinct following the loss of their only prey unless they can change their diet. It has therefore been suggested that an ability of consumers to rewire to novel prey should mitigate the consequences of species loss by reducing the risk of cascading extinction. Using a new modelling approach on natural and computer-generated food webs I find that, on the contrary, rewiring often aggravates the effects of species loss. This is because rewiring can lead to overexploitation of resources, which eventually causes extinction cascades. Such a scenario is particularly likely if prey species cannot escape predation when rare and if predators are efficient in exploiting novel prey. Indeed, rewiring is a two-edged sword; it might be advantageous for individual predators in the short term, yet harmful for long-term system persistence.

    The persistence of an ecological community in a variable world depends on the strength of environmental variation pushing the community away from equilibrium compared to the strength of the deterministic feedbacks, caused by interactions among and within species, pulling the community towards the equilibrium. However, it is not clear which characteristics of a community that promote its persistence in a variable world. In Paper II, using a modelling approach on natural and computer-generated food webs, I show that community persistence is strongly and positively related to its dynamic dimensionality (DD), as measured by the inverse participation ratio (IPR) of the real part of the eigenvalues of the community matrix. A high DD means that the real parts of the eigenvalues are of similar magnitude and the system will therefore approach equilibrium from all directions at a similar rate. On the other hand, when DD is low, one of the eigenvalues has a large magnitude of the real part compared to  the others and the deterministic forces pulling the system towards  equilibrium is therefore weak in many directions compared to the stochastic forces pushing the system away from the equilibrium. As a consequence the risk of crossing extinction thresholds and boundaries separating basins of attractions increases, and hence persistence decreases, as DD decreases. Given the forecasted increase in climate variability caused by global warming, Paper II suggests that the dynamic dimensionality of ecological systems is likely to become an increasingly important property for their persistence.

    In Paper III, I investigate patterns in the size structure of one marine and six running freshwater food webs: that is, how the trophic structure of such ecological networks is governed by the body size of its interacting entities. The data for these food webs are interactions between individuals, including the taxonomic identity and body mass of the prey and the predator. Using these detailed data, I describe how patterns in diet variation and predator variation scales with the body mass of predators or prey, using both a species- and a size-class-based approach. I also compare patterns of size structure derived from analysis of individual-based data with those patterns that result when data are aggregated into species (or size class-based) averages. This comparison shows that analysis based on species averaging can obscure interesting patterns in the size structure of ecological communities. For example, I find that the strength of the relationship between prey body mass and predator body mass is consistently underestimated when species averages are used instead of the individual level data. In some cases, no relationship is found when species averages are used, but when individual-level data are used instead, clear and significant patterns are revealed. These results have potentially important implications for parameterisation of models of ecological communities and hence for predictions concerning their dynamics and response to different kinds of disturbances.

    Paper IV continues the analysis of the highly resolved individual-based empirical data set used in Paper III and investigates patterns and effects of within- and between species resource specialisation in ecological communities. Within-species size variation can be considerable. For instance, in fishes and reptiles, where growth is continuous, individuals pass through a wide spectrum of sizes, possibly more than four orders of magnitude, during the independent part of their life cycle. Given that the size of an organism is correlated with many of its fundamental ecological properties, it should come as no surprise that an individual’s size affects the type of prey it can consume and what predators will attack it (Paper III). In Paper IV, I quantify within- and between species differences in predator species’ prey preferences in natural food webs and subsequently explore its consequences for dynamical dimensionality (Paper II) and community stability in stage structured food web models. Among the natural food webs there are webs where species overlap widely in their resource use while the resource use of size-classes within species differs. There are also webs where differences in resource use among species is relatively large and the niches of sizeclasses within species are more similar. Model systems with the former structure are found to have low dynamical dimensionality and to be less stable compared to systems with the latter structure. Thus, although differential resource use among individuals within a species is likely to decrease the intensity of intraspecific competition and favor individuals specializing on less exploited resources it can destabilize the community in which the individuals are embedded.

    List of papers
    1. Adaptive rewiring aggravates the effects of species loss in ecosystems
    Open this publication in new window or tab >>Adaptive rewiring aggravates the effects of species loss in ecosystems
    2015 (English)In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 6, 8412Article in journal (Other academic) Published
    Abstract [en]

    Loss of one species in an ecosystem can trigger extinctions of other dependent species. For instance, specialist predators will go extinct following the loss of their only prey unless they can change their diet. It has therefore been suggested that an ability of consumers to rewire to novel prey should mitigate the consequences of species loss by reducing the risk of cascading extinction. Using a new modelling approach on natural and computer-generated food webs we find that, on the contrary, rewiring often aggravates the effects of species loss. This is because rewiring can lead to overexploitation of resources, which eventually causes extinction cascades. Such a scenario is particularly likely if prey species cannot escape predation when rare and if predators are efficient in exploiting novel prey. Indeed, rewiring is a two-edged sword; it might be advantageous for individual predators in the short term, yet harmful for long-term system persistence.

    Place, publisher, year, edition, pages
    Nature Publishing Group, 2015
    Keyword
    Resistance, extinction risk, secondary extinction cascades, environmental variation, stochastic, response diversity, functional responses
    National Category
    Biological Sciences
    Identifiers
    urn:nbn:se:liu:diva-108905 (URN)10.1038/ncomms9412 (DOI)000363138400004 ()
    Note

    Funding text: Linkoping University.

    The original titel of this article was Adaptive rewiring aggravates the effects of species loss in ecological networks.

    Available from: 2014-07-11 Created: 2014-07-11 Last updated: 2016-01-21Bibliographically approved
    2. High dynamic dimensionality promotes the persistence of ecological networks in a variable world
    Open this publication in new window or tab >>High dynamic dimensionality promotes the persistence of ecological networks in a variable world
    2016 (English)Manuscript (preprint) (Other academic)
    Abstract [en]

    The long-term persistence of ecological communities depends on the strength of destabilizing stochastic forces relative to the strength of stabilizing feedbacks caused by interactions among and within species. What characteristics of a community that tip the balance of these forces in favour of persistence is not clear. Here we show that long-term persistence of a community is positively related to its dynamic dimensionality (DD). A high DD means that the system approaches the equilibrium from all directions at a similar rate. On the other hand, when DD is low the deterministic forces pulling the system towards equilibrium is weak in many directions compared to the stochastic forces pushing the system away from the equilibrium. As a consequence persistence decreases as DD decreases. This result illustrates the potential importance of dynamic dimensionality of ecosystems for their persistence in a variable world and by extension for their vulnerability to changes in the strength and patterns of climate variability caused by global warming.

    National Category
    Biological Sciences
    Identifiers
    urn:nbn:se:liu:diva-123967 (URN)
    Available from: 2016-01-15 Created: 2016-01-15 Last updated: 2016-01-15Bibliographically approved
    3. Seeing Double: Size-Based and Taxonomic Views of Food Web Structure
    Open this publication in new window or tab >>Seeing Double: Size-Based and Taxonomic Views of Food Web Structure
    Show others...
    2011 (English)In: Advances in Ecological Research, ISSN 0065-2504, Vol. 45, 67-133 p.Article in journal (Refereed) Published
    Place, publisher, year, edition, pages
    Amsterdam: Elsevier Ltd., 2011 Edition: 45
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-71348 (URN)10.1016/B978-0-12-386475-8.00003-4 (DOI)978-0-12-386475-8 (ISBN)
    Available from: 2011-10-12 Created: 2011-10-12 Last updated: 2016-01-15
    4. Patterns of resource utilisation within and between species affect the dynamic dimensionality and stability of ecological communities
    Open this publication in new window or tab >>Patterns of resource utilisation within and between species affect the dynamic dimensionality and stability of ecological communities
    2016 (English)Manuscript (preprint) (Other academic)
    Abstract [en]

    In many ecological communities, individuals within species pass through a wide spectrum of sizes, spanning several orders of magnitude, during the independent part of their life cycle. Such a large size-variation within a species will affect the structure of its niche, since the size of an individual affects the type of prey it can consume as well as what predators will attack it. Here we use highly resolved individual-based empirical data to investigate patterns in the niche structure of several aquatic food webs. We quantify within and between species components of resource use in these webs and explore its consequences for dynamical dimensionality and community stability using simple food web models with stage-structured consumer species. Among the natural food webs there are webs where species overlap widely in their resource use while the resource use of size-classes within species differs. There are also webs where differences in resource use among species is relatively large and the niches of sizeclasses within species are more similar. Model systems with the former structure are found to have low dynamical dimensionality and to be less stable compared to systems with the latter structure. Thus, although differential resource use among individuals within a species is likely to decrease the intensity of intraspecific competition and favor individuals specializing on less exploited resources it can destabilize the community in which the individuals are embedded.

    National Category
    Biological Sciences
    Identifiers
    urn:nbn:se:liu:diva-123968 (URN)
    Available from: 2016-01-15 Created: 2016-01-15 Last updated: 2016-01-15Bibliographically approved
  • 47.
    Gilljam, David
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology. Linköping University, The Institute of Technology.
    Curtsdotter, Alva
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology. Linköping University, The Institute of Technology.
    Ebenman, Bo
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology. Linköping University, The Institute of Technology.
    Adaptive rewiring aggravates the effects of species loss in ecosystems2015In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 6, 8412Article in journal (Other academic)
    Abstract [en]

    Loss of one species in an ecosystem can trigger extinctions of other dependent species. For instance, specialist predators will go extinct following the loss of their only prey unless they can change their diet. It has therefore been suggested that an ability of consumers to rewire to novel prey should mitigate the consequences of species loss by reducing the risk of cascading extinction. Using a new modelling approach on natural and computer-generated food webs we find that, on the contrary, rewiring often aggravates the effects of species loss. This is because rewiring can lead to overexploitation of resources, which eventually causes extinction cascades. Such a scenario is particularly likely if prey species cannot escape predation when rare and if predators are efficient in exploiting novel prey. Indeed, rewiring is a two-edged sword; it might be advantageous for individual predators in the short term, yet harmful for long-term system persistence.

  • 48.
    Gilljam, David
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology. Linköping University, Faculty of Science & Engineering.
    Ebenman, Bo
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology. Linköping University, Faculty of Science & Engineering.
    High dynamic dimensionality promotes the persistence of ecological networks in a variable world2016Manuscript (preprint) (Other academic)
    Abstract [en]

    The long-term persistence of ecological communities depends on the strength of destabilizing stochastic forces relative to the strength of stabilizing feedbacks caused by interactions among and within species. What characteristics of a community that tip the balance of these forces in favour of persistence is not clear. Here we show that long-term persistence of a community is positively related to its dynamic dimensionality (DD). A high DD means that the system approaches the equilibrium from all directions at a similar rate. On the other hand, when DD is low the deterministic forces pulling the system towards equilibrium is weak in many directions compared to the stochastic forces pushing the system away from the equilibrium. As a consequence persistence decreases as DD decreases. This result illustrates the potential importance of dynamic dimensionality of ecosystems for their persistence in a variable world and by extension for their vulnerability to changes in the strength and patterns of climate variability caused by global warming.

  • 49.
    Gilljam, David
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology. Linköping University, Faculty of Science & Engineering.
    Ebenman, Bo
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology. Linköping University, Faculty of Science & Engineering.
    Patterns of resource utilisation within and between species affect the dynamic dimensionality and stability of ecological communities2016Manuscript (preprint) (Other academic)
    Abstract [en]

    In many ecological communities, individuals within species pass through a wide spectrum of sizes, spanning several orders of magnitude, during the independent part of their life cycle. Such a large size-variation within a species will affect the structure of its niche, since the size of an individual affects the type of prey it can consume as well as what predators will attack it. Here we use highly resolved individual-based empirical data to investigate patterns in the niche structure of several aquatic food webs. We quantify within and between species components of resource use in these webs and explore its consequences for dynamical dimensionality and community stability using simple food web models with stage-structured consumer species. Among the natural food webs there are webs where species overlap widely in their resource use while the resource use of size-classes within species differs. There are also webs where differences in resource use among species is relatively large and the niches of sizeclasses within species are more similar. Model systems with the former structure are found to have low dynamical dimensionality and to be less stable compared to systems with the latter structure. Thus, although differential resource use among individuals within a species is likely to decrease the intensity of intraspecific competition and favor individuals specializing on less exploited resources it can destabilize the community in which the individuals are embedded.

  • 50.
    Gilljam, David
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology. Linköping University, The Institute of Technology.
    Thierry, Aaron
    University of Sheffield, UK.
    Edwards, Francois K.
    Centre of Ecology and Hydrology, Wallingford, UK.
    Figueroa, David
    School of BIological and Chemical Sciences, Queen Mary University of London, UK.
    Ibbotson, Anton T.
    Game and Wildlife Conservation Trust, UK.
    Jones, Iwan J.
    School of BIological and Chemical Sciences, Queen Mary University of London, UK.
    Lauridsen, Rasmus B.
    School of BIological and Chemical Sciences, Queen Mary University of London, UK.
    Petchey, Owen L.
    University of Zürick, Switzerland.
    Woodward, Guy
    School of BIological and Chemical Sciences, Queen Mary University of London, UK.
    Ebenman, Bo
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology. Linköping University, The Institute of Technology.
    Seeing Double: Size-Based and Taxonomic Views of Food Web Structure2011In: Advances in Ecological Research, ISSN 0065-2504, Vol. 45, 67-133 p.Article in journal (Refereed)
123 1 - 50 of 122
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