AbstractsBiology & Animal Science

Ecosystems all over the world currently experience dramatic changes in their environment. The direct consequences are increased extinction rates. Food webs, which are networks of predator-prey interactions, provide a basic understanding of ecosystems and therefore help to identify reasonable conservation strategies. In this thesis, I analyze evolutionary metacommunities, which can be modeled as evolutionary networks of networks: The outer networks represent fragmented landscapes of several habitats. The inner networks describe localized food webs on these habitats. New species emerge as modifications of existing species and population dynamics determines how the species interact and which species are viable. Additionally, species are able to migrate between the habitats. In contrast to previous studies that focus either on evolutionary or on spatial aspects, I include both and investigate the interplay between them. I use two different evolutionary food web models to describe the local dynamics. The first model was introduced by Loeuille and Loreau in 2005 [1]. It characterizes a species by its average adult body mass, which is the only evolving trait. The resulting networks show a regular pattern and are remarkably stable. My analysis of several model variants reveals that a model has to fulfill two conditions to provide more realistic network structures: It should allow for the evolution of more traits in addition to body mass and it should restrict each evolving trait to realistic boundaries. Based on these results, I introduce a new model. It is less abstract than earlier models of this type in the sense that all evolving traits have a clear biological meaning. The species are characterized by their average adult body mass, their preferred prey body mass, and the width of their potential prey body mass spectrum. The resulting networks cover a wide range of sizes and structures and show a high similarity to natural food webs. They exhibit a continuous species turnover. However, massive extinction waves that affect more than 50% of the network are not observed, suggesting that corresponding events in earth’s history had external causes. Metacommunities built with the model by Loeuille and Loreau show several results that are already known from non-evolving metacommunity studies. In comparison, metacommunities built with the new model show a much broader range of phenomena. By varying migration strength, migration type and spatial topology, I demonstrate that the combination of evolution and dispersal affects the structure and stability of food webs differently than each of them alone. The understanding of the interplay between evolution and dispersal leads to new insights into the factors that stabilize ecosystems despite changes in the spatial environment or the species composition.