Effects of the aquatic to terrestrial habitat ratio on an amphibian predator and its prey

This dissertation explores the effects of varying the composition of aquatic and terrestrial habitats in a landscape: the aquatic to terrestrial ratio) on amphibians that use both the aquatic and terrestrial habitats during their lives. In Chapter 1, I first used meta-analysis and simulations to demonstrate that as the longevity of an amphibian increases, the elasticity of the population growth rate to perturbations in the aquatic: larval) habitat decreases. In Chapter 2, I examined the abundance of larvae of a long-lived amphibian, Ambystoma maculatum, across landscapes that varied in their aquatic to terrestrial ratios and found that larvae of this species were more dense in landscapes where aquatic habitat was scarce relative to terrestrial habitat. Because larval A. maculatum are top predators, they had more dramatic effects on the community composition of their prey in these isolated habitats, suggesting a result opposite to traditional metacommunity theory. In Chapter 3, I monitored the population level response of two common prey species, tadpoles of grey tree frogs: Hyla versicolor) and Blandchard\u27s cricket frogs: Acris crepitans) to the presence and absence of predatory laval A. maculatum in large-scale experimental ponds. These prey species have very different longevities, and therefore differential use of the aquatic and terrestrial habitats. Population-level results suggest that, as expected, A. maculatum had a larger influence on the population dynamics of the shorter-lived A. crepitans than on H. versicolor. Finally, in Chapter 4, I found that the abundance of aquatic habitat in an area influences the ability of A. maculatum females to discern between oviposition sites of varying qualities. Studies of declining populations of amphibians typically focus on aquatic habitat and factors that affect larval survivorship and growth therein. However, this dissertation highlights the importance of both the aquatic and terrestrial habitats, and the ratio between the two, to overall population dynamics of amphibian species. These results will become more important as anthropogenic habitat destruction not only leads to an absolute loss of habitat, but also potentially alters the ratio of aquatic to terrestrial habitats on which amphibians depend