The evolution and ecology of individual specializations amongst a group of dietary generalists.

Abstract

This dissertation examines individual diet specializations (IS) in a group of ecologically similar and evolutionarily related frogs and toads. Individual specialization is known to have widespread ecological and evolutionary effects.In an initial literature review (Chapter 2) I build a comprehensive theoretical framework showing how different types of population diversity can help, halt, or hinder sympatric speciation. I argue that IS can be maintained indefinitely in populations yet fail to lead to speciation because it is influenced by ecological conditions that may change.Additionally, IS can potentially aid niche partitioning among similar species, increasing species coexistence and resulting in less of the ecological opportunity required to develop more discrete polymorphisms.Stable isotopes are an increasingly common ecological tool for determining diets and habitat usage. However, to use them accurately, researchers need taxon-specific trophic discrimination factors and isotopic incorporation rates on any tissue used for stable isotope analysis. I determined these important isotope properties in adult frogs for the first time (Chapter 3), which not only allows me to use them in the following sections of v! my dissertation, but also allows other researchers to use stable isotopes to study frog and toad diets.Using stable isotope analyses, I examined how IS is influenced by ecological conditions (Chapter 4). I measured IS in five species of frogs and toads and determined which of three ecological parameters (resource diversity, intraspecific competition, and interspecific competition) affected IS in each species. I found that species differed in which ecological parameter best explained IS. Resource diversity most frequently affected IS, with conspecific density second in importance. My results showed that different ecological conditions support IS in different species.Finally, again using stable isotopes, I investigated whether intrapopulation niche variation could aid niche partitioning among the same five species of frogs and toads (Chapter 5). I found that species differed in their niches, but that subsets of individuals overlapped among species. The limited number of individuals overlapping between species decreases their interaction strength, which can contribute to niche partitioning and thus to species coexistence.vi!