Young Scientists Summer Program 2007 Seven Research Projects

Goal To investigate the evolution and stability of mutualistic interactions based on changing interaction topologies, spatially heterogeneous habitats, asymmetries in partner numbers, and processes of partner fidelity and partner choice. Numerous effects sustaining cooperation have been identified since the very first models of cooperation and mutualistic interactions were published. In particular, these early models incorporated mainly static interaction topologies. Such topologies were designed so that a certain member of the population was interacting either within a fixed neighborhood or with the whole population. In contrast, biological experience often shows that individuals can select their interaction partners from an assembly of potential " applicants " (Schwartz & Hoeksema 1998). Once an interaction is established , an individual can also interrupt it again if it is not satisfied with the benefit it thus gains (West et al. 2002). Thus the number and the quality of interactive links of an individual are often expected to change across the population and over time, leading to a dynamic interaction topology. Such dynamism may apply to interactions involving both interspecific and intraspecific cooperation. Even when mutualistic relationships are obligatory for the participants, a particular interaction with a single partner can thus still be conditional. The larger the supply of potential partners, the easier it is to dispose non-mutualistic partners (cheaters) and seek out better mutualistic partners. This leads to the dynamic formation and loss of contacts between individuals, resulting in a changing composition of interacting groups. The distinction between partner fidelity (PF) and partner choice (PC) models was first considered by Bull and Rice (1991). PF models focus on the termination of contacts between individuals of two species, while PC models, interpreting the cooperative act as a good offered in a biological marketplace, focus on the initiation of contacts between individuals of two species. The majority of modeling work in the field of cooperation and mutualistic interactions has incorporated partner fidelity. The same applies to a model of mutualism by Doebeli and Knowlton (1998), which I have previously used to explore the effects of spatial heterogeneity on the evolution and stability of mutualism (Boza and Scheuring 2004). My previous model was based on a fixed interacting neighborhood, so that an individual could only choose its partner from the same location on a grid. Only the intraspecies competition could lead to changes in the interspecific allocation of partners. A spatial game-theoretical model incorporating both partner fidelity and …