My main research interests are structural ecosystem shifts in shallow lakes and processes behind local adaptive change that follow from such shifts. Shallow eutrophic lakes tend to appear in two alternative states, one characterised by abundant submerged vegetation and clear water, the other by turbid water and sparse vegetation. Each state can be stabilised by feedback mechanisms that include both biotic and abiotic components. However, a large enough disturbance can force the system to shift to the alternate state. To understand these dynamics it is fundamental to identify the driving feedback systems. Two organism groups know to be important for the dynamics are benthivorous fish and submerged vegetation. However, still much of the involved interactions remain to be understood. For instance, are evolutionary effects important? Recent studies show that after a shift to dominance of submerged vegetation, the freshwater isopod (Asellus aquaticus L.) that colonize stonewort stands change phenotype towards a smaller and lighter pigmented ecotype. Our present studies focus on the ecological settings that promote or limit the evolutionary processes behind these adaptive changes. A second, but less intersting question is to what extent the evolutionary changes are part of the establishment of the new set of feedback systems that may stabilise the ecosystem.
Selected publications on shallow lake ecosystem change and feedback mechanisms
Hargeby, A, Blindow, I. & Andersson, G. 2007. Long-term patterns of shifts between clear and turbid states in Lake Krankesjön and Lake Tåkern. - Ecosystems 10:28-35.
Hargeby, A, Jonzén, N. & Blindow, I. 2006. Does a long-term oscillation in nitrogen concentration reflect climate impact on submerged vegetation and vulnerability to state shifts in a shallow lake? - Oikos 115:334-348.
Blindow, I., Hargeby, A., Meyercordt, J., Schubert, H. 2006. Primary production in two shallow lakes with contrasting plant form dominance: A paradox of enrichment? - Limnology and Oceanography 51:2711-2721.
Hargeby,A., Blom, H., Blindow, I. & Andersson, G. 2005. Expanding submerged vegetation influences growth and population structure of perch, Perca fluviatilis, in a eutrophic lake. - Freshwater Biology 50:2053-2062.
Hargeby, A., Blindow, I. & Hansson, L-A. 2004. Shifts between clear and turbid states in a shallow lake: multi-causal stress from climate, nutrients and biotic interactions – Archiv für Hydrobiologie 161:433-454.
Selected publications on local adaptive change in Asellus populations
Eroukhmanoff, F, Hargeby, A., Nowshiravani Arnberg, N, Hellgren, O, Bensch, S. & Svensson, E. 2009. Parallelism, historical contingency and phenotype sorting in ecotype divergence of a freshwater isopod. - Journal of Evolutionary Biology 22:1098-1110.
Hargeby, A. & Erlandsson, J. 2006. Is size-assortative mating important for the evolution of colour differentiated populations of a freshwater isopod. - Journal of EvolutionaryBiology 19:1911-1919.
Hargeby, A., Stoltz, J. & Johansson, J. 2005. Locally differentiated cryptic pigmentation in the freshwater isopod Asellus aquaticus. - Journal of Evolutionary Biology 18:713-721.
Hargeby, A, Johansson, J. & Ahnesjö. 2004. Habitat specific pigmentation in a freshwater isopod – adaptive evolution over a small spatiotemporal scale –Evolution 58:81-94.