Dissertation Research: Effects of the aquatic:terrestrial habitat ratio on an amphibian predator and its prey

Washington University, Saint Louis MO

Investigators

Abstract

Habitat destruction can change the degree of isolation and shape of remaining habitats, and thus can have dramatic consequences for biodiversity and the functioning of ecosystems. Although less appreciated, disproportionate destruction of one type of habitat will also change the ratio of distinct habitat types in a landscape. For example, wetland draining will not only decrease the amount of aquatic habitat in a landscape, but will also decrease the ratio of aquatic to terrestrial habitats. For organisms that require the use of both aquatic and terrestrial habitat types, such as amphibians, changes in the ratio of aquatic to terrestrial habitats can alter their abundance in either habitat, as well as their overall population dynamics. Preliminary surveys of a long lived amphibian, Ambystoma maculatum (the spotted salamander), indicate that the abundance of larval A. maculatum in aquatic habitats depends critically upon the ratio of aquatic to terrestrial habitat available. Because larval A. maculatum are top predators in small fishless ponds, they can have dramatic effects on community composition and diversity of their prey; alterations to the ratio of aquatic to terrestrial habitats can alter the strengths of this effect. This research seeks to elucidate the relationship between the ratio of aquatic to terrestrial habitats in a landscape and the impacts of larval A. maculatum on the aquatic community. It will specifically focus on the influence, of A. maculatum predation on the population dynamics of two frog species that utilize terrestrial and aquatic habitats to different extents, using mark-recapture and demographic modeling approaches. Studies of declining populations of amphibians typically focus on aquatic habitat and factors that affect larval survivorship and growth therein. Yet, there is increasing evidence of the importance of terrestrial habitat for many amphibian populations. Understanding how amphibians will respond to different types of habitat destruction (e.g., deforestation, draining of wetlands) requires consideration of the entire life-cycle of amphibians, and the ratio of aquatic to terrestrial habitats within the landscape. This research will be a timely contribution to the conservation literature and to management efforts aimed at preventing future extinctions of amphibians.