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Extinctions in Ecological Communities: direct and indirect effects of perturbation on biodiversity
Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology. Linköping University, The Institute of Technology.
2014 (English)Doctoral 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.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2014. , 60 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1609
National Category
Other Natural Sciences
Identifiers
URN: urn:nbn:se:liu:diva-108906DOI: 10.3384/diss.diva-108906ISBN: 978-91-7519-278-9 (print)OAI: oai:DiVA.org:liu-108906DiVA: diva2:733833
Public defence
2014-08-29, Schrödinger, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2014-07-11 Created: 2014-07-11 Last updated: 2017-04-19Bibliographically approved
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
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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
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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
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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: 2017-12-08Bibliographically 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: 2017-12-05Bibliographically approved

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