Publication Date

2008-04-21

Availability

Open access

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PHD)

Department

Biology (Arts and Sciences)

Date of Defense

2008-03-28

First Committee Member

Julian Lee - Committee Chair

Second Committee Member

Don DeAngelis - Committee Member

Third Committee Member

Matt Potts - Committee Member

Fourth Committee Member

Raymond Semlitsch - Committee Member

Abstract

Habitat modification is the primary cause of amphibian population declines worldwide. Some species survive in modified habitats whereas others become restricted to small, isolated forest patches. Although many studies compare species richness and composition between modified and intact habitats, the factors and mechanisms that maintain biodiversity in these landscapes are poorly understood. I asked how life history traits and habitat features influence interspecific variation in frog occupancy patterns in tropical pasture and forest. To identify mechanisms underlying occupancy patterns, I used experiments to examine how abiotic conditions in different habitats influence the vital rates of tadpoles. I also explored whether tadpoles use a carnivorous foraging strategy to improve performance in nutrient-poor, ephemeral pools in pasture. Although modified and intact habitats offer abiotic environments that differ in quality for frogs, pastures contribute to the maintenance of biodiversity in fragmented landscapes. I detected an equal number of species but substantially different assemblage composition in forest and pasture. Species that occurred in pasture had different traits than those in forest, including larger body sizes, larger clutch sizes, larger geographic ranges, and reproductive modes that depend on water. The occurrence of pasture-specialists was associated with habitat features at small spatial scales, whereas the occurrence of forest-specialists was associated with habitat features at small and large spatial scales. An experiment indicated that abiotic conditions in pastures may deter or facilitate adult movements to breeding sites. Behavioral selection of sites by two model species was consistent with tadpole performance. Tadpoles of a pasture-specialist performed well across the pasture-forest gradient, but abiotic conditions in pasture facilitated faster growth and development than in edge or forest. In contrast, tadpoles of a forest-specialist performed well only in edge and forest. Most tadpoles occupying ephemeral pasture pools were facultative carnivores or cannibals of eggs and hatchlings. Tadpoles may contribute to the regulation of assemblages in pasture pools, influencing the relative abundance and composition of species through differential predation on eggs and hatchlings. The study of factors and mechanisms that contribute to population growth or decline of species can facilitate understanding of assemblage-level patterns of amphibian diversity in modified landscapes.

Keywords

Community Ecology; GIS; Population Ecology; Mesocosms; Osa Peninsula; Costa Rica

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