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  • 1.
    Blindow, Irmgard
    et al.
    Ernst Moritz Arndt University of Greifswald, Germany .
    Hargeby, Anders
    Linköping University, Department of Physics, Chemistry and Biology, Biology. Linköping University, The Institute of Technology.
    Hilt, Sabine
    Leibniz Institute Freshwater Ecol and Inland Fisheries, Germany .
    Facilitation of clear-water conditions in shallow lakes by macrophytes: differences between charophyte and angiosperm dominance2014In: Hydrobiologia, ISSN 0018-8158, E-ISSN 1573-5117, Vol. 737, no 1, p. 99-110Article in journal (Refereed)
    Abstract [en]

    A number of mechanisms result in a feedback between water clarity and macrophytes and, consequently, the occurrence of alternative stable states in shallow lakes. We hypothesize that bottom-up mechanisms and interactions within the benthic food web are more important in a charophyte-dominated clear-water state, while top-down mechanism and interactions in the planktonic food web prevail at angiosperm dominance. Charophytes, which dominate at lower nutrient concentrations and develop higher densities than most angiosperms, can have a higher influence on sedimentation, resuspension, and water column nutrients. During dominance of dense submerged vegetation like charophytes, zooplankton can be hampered by low food quality and quantity and by high predation pressure from juvenile fish, which in turn are favoured by the high refuge potential of this vegetation. Grazing pressure from zooplankton on phytoplankton can therefore be low in charophytes, but the main feedback in angiosperm-dominated ecosystems. Charophytes offer a higher surface than most angiosperms to periphyton, which favors benthic invertebrates. These support macrophytes by grazing periphyton and constitute a central link in a trophic cascade from fish to periphyton and macrophytes. To test these hypotheses, more experiments and field measurements comparing the effect of charophytes and angiosperms on water clarity are needed.

  • 2.
    Blindow, Irmgard
    et al.
    Biological Station of Hiddensee, University of Greifswald, Germany.
    Hargeby, Anders
    Linköping University, Department of Physics, Chemistry and Biology, Biology. Linköping University, The Institute of Technology.
    van de Weyer, Klaus
    Lanaplan GbR, Germany.
    Submerged vegetation in shallow lakes2012In: Encyclopedia of lakes and estuaries / [ed] Bengtsson, L, Herschy, R. & Fairbridge, R.W., Springer-Verlag New York, 2012, p. 747-751Chapter in book (Refereed)
  • 3.
    Eroukhmanoff, F
    et al.
    Section for Animal Ecology, Lund University, Lund, Sweden.
    Hargeby, Anders
    Linköping University, Department of Physics, Chemistry and Biology, Biology. Linköping University, The Institute of Technology.
    Arnberg, N N
    Department of Ecology & Evolutionary Biology, University of California, Santa Cruz, CA, USA.
    Hellgren, O
    The EGI, Department of Zoology, Oxford, UK.
    Bensch, S
    Section for Animal Ecology, Lund University, Lund, Sweden.
    Svensson, E I
    Section for Animal Ecology, Lund University, Lund, Sweden.
    Parallelism and historical contingency during rapid ecotype divergence in an isopod2009In: Journal of Evolutionary Biology, ISSN 1010-061X, E-ISSN 1420-9101, Vol. 22, no 5, p. 1098-1110Article in journal (Refereed)
    Abstract [en]

    Recent studies on parallel evolution have focused on the relative role of selection and historical contingency during adaptive divergence. Here, we study geographically separate and genetically independent lake populations of a freshwater isopod (Asellus aquaticus) in southern Sweden. In two of these lakes, a novel habitat was rapidly colonized by isopods from a source habitat. Rapid phenotypic changes in pigmentation, size and sexual behaviour have occurred, presumably in response to different predatory regimes. We partitioned the phenotypic variation arising from habitat (selection: 81-94%), lake (history: 0.1-6%) and lake x habitat interaction (unique diversification: 0.4-13%) for several traits. There was a limited role for historical contingency but a strong signature of selection. We also found higher phenotypic variation in the source populations. Phenotype sorting during colonization and strong divergent selection might have contributed to these rapid changes. Consequently, phenotypic divergence was only weakly influenced by historical contingency.

  • 4.
    Eroukhmanoff, Fabrice
    et al.
    Section for Animal Ecology, Ecology Building, Lund University, Lund, Sweden.
    Hargeby, Anders
    Linköping University, Department of Physics, Chemistry and Biology, Biology. Linköping University, The Institute of Technology.
    Svensson, Erik I
    Section for Animal Ecology, Ecology Building, Lund University, Lund, Sweden.
    Rapid adaptive divergence between ecotypes of an aquatic isopod inferred from F-ST-Q(ST) analysis2009In: Molecular Ecology, ISSN 0962-1083, E-ISSN 1365-294X, Vol. 18, no 23, p. 4912-4923Article in journal (Refereed)
    Abstract [en]

    Divergent natural selection is often thought to be the principal factor driving phenotypic differentiation between populations. We studied two ecotypes of the aquatic isopod Asellus aquaticus which have diverged in parallel in several Swedish lakes. In these lakes, isopods from reed belts along the shores colonized new stonewort stands in the centre of the lakes and rapid phenotypic changes in size and pigmentation followed after colonization. We investigated if selection was likely to be responsible for these observed phenotypic changes using indirect inferences of selection (F-ST-Q(ST) analysis). Average Q(ST) for seven quantitative traits were higher than the average F-ST between ecotypes for putatively neutral markers (AFLPs). This suggests that divergent natural selection has played an important role during this rapid diversification. In contrast, the average Q(ST) between the different reed ecotype populations was not significantly different from the mean F-ST. Genetic drift could therefore not be excluded as an explanation for the minor differences between allopatric populations inhabiting the same source habitat. We complemented this traditional F-ST-Q(ST) approach by comparing the F-ST distributions across all loci (n = 67-71) with the Q(ST) for each of the seven traits. This analysis revealed that pigmentation traits had diverged to a greater extent and at higher evolutionary rates than size-related morphological traits. In conclusion, this extended and detailed type of F-ST-Q(ST) analysis provides a powerful method to infer adaptive phenotypic divergence between populations. However, indirect inferences about the operation of divergent selection should be analyzed on a per-trait basis and complemented with detailed ecological information.

  • 5.
    Eroukhmanoff, Fabrice
    et al.
    Section for Animal Ecology, Ecology Building, Lund University, Lund, Sweden.
    Hargeby, Anders
    Linköping University, Department of Physics, Chemistry and Biology, Biology. Linköping University, The Institute of Technology.
    Svensson, Erik I.
    Section for Animal Ecology, Ecology Building, Lund University, Lund, Sweden.
    THE ROLE OF DIFFERENT REPRODUCTIVE BARRIERS DURING PHENOTYPIC DIVERGENCE OF ISOPOD ECOTYPES2011In: Evolution, ISSN 0014-3820, E-ISSN 1558-5646, Vol. 65, no 9, p. 2631-2640Article in journal (Refereed)
    Abstract [en]

    The question of how diverging populations become separate species by restraining gene flow is a central issue in evolutionary biology. Assortative mating might emerge early during adaptive divergence, but the role of other types of reproductive barriers such as migration modification have recently received increased attention. We demonstrate that two recently diverged ecotypes of a freshwater isopod (Asellus aquaticus) have rapidly developed premating isolation, and this isolation barrier has emerged independently and in parallel in two south Swedish lakes. This is consistent with ecological speciation theory, which predicts that reproductive isolation arises as a byproduct of ecological divergence. We also find that in one of these lakes, habitat choice acts as the main barrier to gene flow. These observations and experimental results suggest that migration modification might be as important as assortative mating in the early stages of ecological speciation. Simulations suggest that the joint action of these two isolating barriers is likely to greatly facilitate adaptive divergence, compared to if each barrier was acting alone.

  • 6.
    Hansson, Lars-Anders
    et al.
    Institute of Ecology, Lund University, Ecology Building, Lund, Sweden.
    Nicolle, Alice
    Institute of Ecology, Lund University, Ecology Building, Lund, Sweden.
    Bronmark, Christer
    Institute of Ecology, Lund University, Ecology Building, Lund, Sweden.
    Hargeby, Anders
    Linköping University, Department of Physics, Chemistry and Biology, Biology. Linköping University, The Institute of Technology.
    Lindstrom, Ake
    Institute of Ecology, Lund University, Ecology Building, Lund, Sweden.
    Andersson, Gunnar
    Institute of Ecology, Lund University, Ecology Building, Lund, Sweden.
    Waterfowl, macrophytes, and the clear water state of shallow lakes2010In: Hydrobiologia, ISSN 0018-8158, E-ISSN 1573-5117, Vol. 646, no 1, p. 101-109Article in journal (Refereed)
    Abstract [en]

    The importance of lake ecosystems for waterfowl remains a topic of debate. In order to assess how temporal variations in lake features, specifically shifts between alternative stable states, may interact with the waterfowl fauna, we performed a long-term (22 years) study of the shallow Lake Krankesjon, southern Sweden. Lower total numbers of waterfowl occurred during periods with low macrophyte cover and turbid water, than when submersed macrophytes flourished and the water was clear. Some specific functional groups of waterfowl, such as herbivores, invertebrate, and fish feeders, showed a positive relation to clear water and high macrophyte cover. Hence, our data suggest that some migratory waterfowl may select lakes based on water quality, thereby adjusting their large-scale migratory routes. On the other hand, omnivorous waterfowl exhibited their highest abundances during turbid conditions. Furthermore, waterfowl not primarily relying on food from the lake showed no response to fluctuations in turbidity or macrophyte cover, but followed regional trends in population dynamics. In our study lake, L. Krankesjon, we estimated that waterfowl remove less than 3% of the macrophyte biomass during a stable clear-water state with lush macrophyte beds. However, during transition periods between alternative stable states, when macrophyte biomass is lower and the plants already stressed, the consumption rate of waterfowl may have a stronger effect on lake ecosystem functioning.

  • 7.
    Hargeby, Anders
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Biology. Linköping University, The Institute of Technology.
    Blindow, Irmgard
    Biological Station of Hiddensee, University of Greifswald, Germany.
    Alternative stable states in shallow lakes2012In: Encyclopedia of lakes and estuaries / [ed] Bengtsson, L, Herschy, R. & Fairbridge, R.W., Springer-Verlag New York, 2012, p. 9-13Chapter in book (Refereed)
  • 8.
    Hargeby, Anders
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Biology.
    Blindow, Irmgard
    University of Lund.
    Andersson, Gunnar
    University of Lund.
    Long-term patterns of shifts between clear and turbid states in Lake Krankesjon and Lake Takern2007In: Ecosystems (New York. Print), ISSN 1432-9840, E-ISSN 1435-0629, Vol. 10, no 1, p. 28-35Article in journal (Refereed)
    Abstract [en]

    During the past century, Lake Takern and Lake Krankesjon, southern Sweden, have shifted repeatedly between a state of clear water and abundant submerged vegetation, and a state of turbid water and sparse vegetation. Long-term empirical data on such apparently alternative stable state dynamics are valuable as complements to modeling and experiments, although the causal mechanisms behind shifts are often difficult to identify in hindsight. Here, we summarize previous studies and discuss possible mechanisms behind the shifts. The most detailed information comes from monitoring of two recent shifts, one in each lake. In the 1980s, L. Krankesjon shifted to clear water following an expansion of sago pondweed, Potamogeton pectinatus. Water clarity increased when the pondweed was replaced by characeans. Zooplankton biomass in summer declined and the concentration of total phosphorus (TP) was reduced to half the previous level. The fish community changed over several years, including an increasing recruitment of piscivorous perch (Perca fluviatilis). An opposite directed shift to turbid water occurred in Lake Takern in 1995, when biomass of phytoplankton increased in spring, at the expense of submerged vegetation. Consistent with the findings in L. Krankesjon, phyto- and zooplankton biomass increased and the average concentration of TP doubled. After the shift to clear water in L. Krankesjon, TP concentration has increased during the latest decade, supporting the idea that accumulation of nutrients may lead to a long-term destabilization of the clear water state. In L. Takern, data on TP are inconclusive, but organic nitrogen concentrations oscillated during a 25-year period of clear water. These observations indicate that intrinsic processes cause gradual or periodic changes in system stability, although we cannot exclude the possibility that external forces are also involved. During such phases of destabilization of the clear water state, even small disturbances could possibly trigger a shift, which may explain why causes behind shifts are hard to identify even when they occur during periods of extensive monitoring.

1 - 8 of 8
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