On the origin of polymorphism - consequences of competition and predation in heterogeneous environments

Abstract: In this thesis, I have studied when an initially monomorphic population can diverge into two morphs in a heterogeneous environment. Evolution is driven by competition for resources or predation. In Paper I, we studied source-sink dynamics during evolution in an environment with two types of resource of different abundance in two habitats. We found that dispersal can help maintain higher diversity and that source-sink dynamics can give an ecologically persistent community, which is not evolutionary persistent. Paper II-Iv consist of studies of the evolution of polymorphic crypsis. In Paper II we compared the effect on evolution of different predatory functional responses (with fixed predator abundance), and found that type III functional response had a much larger parameter space where polymorphism could evolve, compared to type II functional response. Also, polymorphism was most likely to evolve for intermedate predation and trade-off, and low dispersal. In Paper III, I compared three different predator-prey models (with explicit dynamics for all population), with passive dispersal, isolation or habitat choice, and found little difference between the results. However, the functional response type II here gave very similar result to the type III functional response in Paper II. In Paper IV we used an artificial neural network to simulate a learning predator. The sexually reproducing prey could evolve polymorphic crypsis when invading a visually different habitat if there were little dispersal between the old and the new habitat. Too high dispersal would produce an intermediate morph, and for very high dispersal the prey could not become adapted to its new enironment at all.