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Evolutionary consequences of ecological interactions

Evolutionary consequences of ecological interactions
Etsuko Nonaka


Department of Ecology and Environmental Science, Umeå University 90 187Umeå, SWEDEN.


Eco-evolutionary dynamics integrates the reciprocal interactions between ecology and evolution. These two branches of biology traditionally assume the other as static for simplicity. However, increasing evidence shows that this simplification may not always hold because ecology and evolution can operate in similar timescales. This thesis theoretically explores how the reciprocal interactions may influence ecological and evolutionary outcomes in four different eco-evolutionary contexts.

Many species of non-social animals live in groups. Aggregating in groups often has both benefits and costs that depend on group size. Thanks to the benefits of aggregation, population growth likely depends positively on population density when it is small. This phenomenon, the Allee effect, has been hypothesized to explain the evolution of aggregation behavior. I find that the Allee effect alone does not lead to the evolution when population dynamics is explicitly accounted for. Some other mechanisms, such as frequent needs for colonizing new patches or anti-aggregation, should be invoked to explain why aggregation behavior could evolve.

Phenotypic plasticity is the ability of a genotype to express distinct phenotypes when exposed to different environments. Although it is often shown to be adaptive and not costly, highly plastic organisms are rare. Past studies demonstrated some potential reasons. I test another possibility; costs may arise from sexual selection because highly plastic individuals may be less preferred as a mate. I show that, even in the absence of the direct cost of plasticity, the level of plasticity remained low at intermediate strengths of assortative mating. This pattern is robust across wide ranges of parameter values.

Ecological speciation occurs when ecologically divergent selection between environments causes reproductive isolation between diverging subpopulations. Several verbal models of ecological speciation emphasize the roles of phenotypic plasticity in promoting speciation. The complex processes involved in speciation, however, are difficult to be evaluated by verbal accounts. I quantitatively test the proposed idea in a mechanistic model of ecological speciation in the presence and absence of plasticity. I find conditions under which plasticity can promote or hinder ecological speciation. Plasticity facilitates speciation by producing a gap in the distributions of expressed phenotypes, which serves as a barrier to gene flow in an assortatively mating population.

Ecosystem ecology and evolutionary biology are the least integrated fields in ecology and evolution. Natural selection operating at the individual levels on traits governing ecosystem functions may affect ecosystem properties, which may feedback to individuals. I reviewed this idea and demonstrate the feedback loop by using a simple consumer-resource model.