Conservation of California red -legged frogs: Distribution correlates, spatial dynamics and behavioral interactions with an invasive species.

摘要

This research investigated key aspects of amphibian ecology using a combination of site surveys to determine occupancy by species, mark-recapture, radio-telemetry techniques and behavioral observations. Though linked both theoretically and thematically, this research was divided into five discrete chapters.;In the first chapter, I used a combination of field techniques and GIS analyses to investigate amphibian habitat use in forty wetlands in the Elkhorn Slough watershed, central California. I investigated factors correlated with distribution of Pacific chorus frogs, California red-legged frogs, and invasive American bullfrogs. I found differences in the relationships of these species to factors such as poor water quality, degree of isolation, and proximity to roads, and I hypothesize that sensitivity to these factors may contribute to species decline.;In my second chapter, I documented high rates of interspecific amplexus between California red-legged frog males and bullfrog juveniles. I suggest that this male behavior fits the definition of an evolutionary trap, when formerly adaptive behaviors, specifically mate choice, become maladaptive. California red-legged frogs are the largest native western frogs, females are larger than males on average, and female anuran size and fecundity are positively correlated. Male preference for the largest frog was historically adaptive, but has likely become maladaptive throughout the range of the California red-legged frog, much of which now overlaps the bullfrog's introduced distribution.;In my third chapter, I used invasive species removal and behavioral observations to document two different effects of invasive American bullfrogs on the behavior of native California red-legged frogs. I specifically found that these invaders impact ontogenetic resource partitioning in the California red-legged frog, causing adults to share space with smaller frogs. Adult bullfrog presence also caused California red-legged frog adults to obscure themselves more thoroughly and for all age classes to use different vegetation for cover.;In my fourth chapter, I used site surveys and mark-recapture efforts in a subset of the ponds to explicitly test whether California red-legged frogs exhibit metapopulation dynamics. I found that while they do fulfill the requirements, these dynamics likely occur at scales much larger than typically studied, and that discrete ponds do not generally represent discrete subpopulations.;Lastly, I used mark-recapture analyses in the program MARK to estimate survivorship of California red-legged frogs. I combined this work with estimation of growth rates in this species, which will allow the construction of demographic models for threatened California red-legged frogs. This chapter also integrates this new information with explicit movement data to make management recommendation for the species.