Wir bitten um Entschuldigung

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Dr. Christian Guill

Research interests


Structure and stability of food webs


Food webs, the networks of 'who eats whom' in ecosystems, are key to our understanding of the functioning of ecosystems. Considering the pace of global biodiversity loss and its impact on the services provided by ecosystems, it is vital to understand the mechanisms that stabilise these large and complex networks.


Traditionally, mathematical models of population dynamics treat species as homogeneous entities and only account for feeding, reproduction, and mortality as dynamical processes. They thus neglect individual development and maturation. These models also neglect differences in body size among the individuals of a population, which may influence their feeding habits and their vulnerability to predation. I am particularly interested in how the ontogenetic structure of populations (i.e., juvenile and adult stages or different size/age classes) affects the composition of food webs and their dynamical stability, which I mainly study using computer simulations of mathematical models.


Dynamics of structured populations


The dynamics of ontogenetically structured populations can be significantly different from that of unstructured populations. Populations with two ontogenetic stages (juveniles and adults) can be dominated by either of the stages and it is possible that these different population states coexist under identical environmental conditions as alternative stable states. This has important consequences for the conservation of these species and their consumers.


Species with multiple consecutive stages or a continuous size structure can exhibit so-called single-generation cycles. These population oscillations have a period that is close to the dominant generation time of the species. Recently I have started analysing the population dynamics of the Pacific sockeye salmon. The populations of this anadromous fish species often have a clear, discrete age structure. Several of the salmon stocks that spawn in the Fraser River basin in British Columbia, Canada, display large amplitude oscillations with a period of four years. I am interested in the mathematical mechanism that stabilises the single-generation cycles in this system. This may not only have implications for the management of this economically important salmon species, but may also provide a generic mechanism for population oscillations in species with discrete age structure.


Publications
2012
Schmitt, C.K., Guill, C. & Drossel, B. (2012): The robustness of cyclic dominance under random fluctuations. Journal of Theoretical Biology, 308: 79-87, doi:10.1016/j.jtbi.2012.05.028


Plitzko, S.J., Drossel, B. & Guill, C. (in press): Complexity–stability relations in generalized food-web models with realistic parameters. Journal of Theoretical Biology 306: 7-14, doi: 10.1016/j.jtbi.2012.04.008


Heckmann, L., Drossel, B., Brose, U. & Guill, C. (2012): Interactive effects of body-size structure and adaptive foraging on food-web stability. Ecology Letters, doi: 10.1111/j.1461-0248.2011.01733.x


2011


Guill, C.; Drossel, B.; Just, W.; Carmack, E. (2011): A three-species model explaining cyclic dominance of pacific salmon. Journal of Theoretical Biology 276 (1): 16-21, DOI:10.1016/j.jtbi.2011.01.036.


Guill, C.; Reichardt, B.; Drossel, B.; Just, W. (2011): Coexisting patterns of population oscillations: the degenerate Neimark-Sacker bifurcation as a generic mechanism. Physical Review E 83 (2): 021910, DOI:10.1103/PhysRevE.83.021910.


2010
Kartascheff, B.; Heckmann, L.; Drossel, B.; Guill, C. (2010): Why allometric scaling enhances stability in food web models. Theoretical Ecology 3 (3): 195-208, DOI:10.1007/s12080-009-0063-3.


Guill, C. (2010): A Model of Large-Scale Evolution of Complex Food Webs. Mathematical Modelling of Natural Phenomena 5 (6): 139-158.


2009


Guill, C: Alternative dynamical states in stage-structured consumer populations. Theoretical Population Biology 76 (3): 168-178, DOI:10.1016/j.tpb.2009.06.002.


Kartascheff, B.; Guill, C.; Drossel, B.: Positive complexity-stability relations in food web models without foraging adaptation. Journal of Theoretical Biology 259 (1): 12-23, DOI:10.1016/j.jtbi.2009.03.012.


2008


Guill, C.; Drossel, B.: Emergence of complexity in evolving niche-model food webs. Journal of Theoretical Biology 251 (1): 108-120; DOI:10.1016/j.jtbi.2007.11.017.


Rall, B.C., Guill, C. & Brose, U. (2008): Food-web connectance and predator interference dampen the paradox of enrichment. Oikos 117: 202-213.