Date of Award

8-2005

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Ecology and Evolutionary Biology

Major Professor

Arthur C. Echternacht

Committee Members

James A. Drake, Michael L. McKinney, Daniel Simberloff

Abstract

Although invasive species are considered to be a significant threat to native biodiversity, the impacts of very few nonindigenous species are well known. In this dissertation I describe the results of several studies evaluating the impacts of the presence of nonindigenous amphibians and reptiles in Florida. I conducted an analysis to assess the patterns and effects on biodiversity of the establishment of nonindigenous amphibians and reptiles in Florida at the county level. The richness of the 40 established nonindigenous amphibians and reptiles is not distributed evenly across the state, but instead is significantly greater in the southern part of the state and in counties with large human populations. These trends likely reflect the recent breakdown of historical barriers to invasion between Florida and the Caribbean region and the influence of human activities in the establishment of nonindigenous species. I also conducted several experimental case studies of the effects of the presence of the tadpoles of two invasive amphibians, the cane toad (Bufo marinus) and the Cuban treefrog (Osteopilus septentrionalis), in native Floridian tadpole communities. These studies indicated that B. marinus does not significantly affect native tadpoles through competition, while O. septentrionalis tadpoles outcompete and adversely affect native tadpoles, both in laboratory microcosms and naturalistic outdoor mesocosms. Larval O. septentrionalis also prey on native tadpoles, but this effect is probably not significant under natural conditions when alternative food is present. A mechanistic laboratory study indicated that the competitive effects of O. septentrionalis were mediated through exploitation competition with no evidence of interference competition. When keystone predators, eastern newts (Notophthalmus viridescens), were included in the experimental tadpole communities, the negative effects of O. septentrionalis tadpoles on native tadpoles were reduced significantly. Higher mortality of O. septentrionalis larvae suggests that newts preyed selectively on O. septentrionalis tadpoles, supporting their role as keystone predators. If general, this result suggests that keystone predators are important to the maintenance of diversity in invaded communities. Collectively, these results suggests that O. septentrionalis larvae may affect native amphibian populations in Florida through larval interactions, but these impacts may be limited by the presence of keystone predators.

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