Background
It is now widely accepted that some amphibian populations are declining around the globe, but in many cases the causes of these declines remain unknown. Because amphibians are sensitive to so many natural as well as anthropogenic factors, identifying specific variables affecting amphibian health can be a daunting task. Unveiling the effects of these factors on amphibian populations is further complicated by the fact that many amphibians exhibit complex life cycles, where a portion of the lifecycle is spent in water and another in the terrestrial environment. Thus, environmental variables can directly affect one life stage, but ultimately affect other life stages via changes in recruitment or reproduction. The figure below outlines some of the factors that are known to affect amphibians and some of the complex relationships that exist among them.

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A simplified diagram representing the effects of natural and anthropogenic stressors on an amphibian with a complex lifecycle. Exposure to one or more stressors can reduce reproductive output (large green arrow) of terrestrial life stages. Alternatively, stressors in the aquatic environment can reduce recruitment (large blue arrow) to the terrestrial environment, thus reducing the number of potential breeding individuals in the population. Solid red arrows represent the direct effect of stressors on a particular life stage. The box encloses stressors that affect both terrestrial and aquatic life stages. Dashed arrows represent demonstrated relationships where one stressor may enhance the effects or exposure to another stressor. Other complex relationships between stressors are possible but not yet realized.
Figure drawing by Brandon P. Staub. Figure from Rowe, Hopkins, and Bridges. In Press. “Physiological Ecology of Amphibians in Relation to Susceptibility to Natural and Anthropogenic Factors” In The global decline of amphibians: An integrated analysis of multiple stressor effects. Eds Linder, G., Crest, S., Sparling, D. SETAC Press, Pensacola.
Specific Research Objectives
Because of fascinating physiological and life history attributes of amphibians and global concern over their health, amphibians are one of the primary focal points of research in the Wildlife Ecotoxicology and Physiological Ecology Program. Our research specifically seeks to understand how natural and environmental factors can act independently, and through complex interactions, to affect the physiological ecology of amphibians. We primarily focus on the effects of environmental contaminants on physiological and life history traits that ultimately have implications for fitness and population dynamics.

Much of our research has focused on how contaminants alter the developmental trajectories of larval amphibians. Use of amphibian life history traits, such as age and size at metamorphosis, as toxicological response variables can provide insight into the subtle effects of environmental perturbations on the health of amphibian populations. Using traditional ecological studies of pond desiccation, competition, and predation as a foundation for our toxicological work, we have conducted field, mesocosm, and controlled laboratory studies to evaluate the direct and indirect effect of contaminants on amphibian life history traits. The following figure summarizes some of the alternative outcomes of traditional ecological studies of amphibian development. We are finding that environmental contaminants can produce similar alterations in developmental trajectories.

A schematic diagram outlining the dynamic interplay between environmental variables and the timing of metamorphosis in amphibian larvae. In comparison to the developmental trajectory of amphibian larvae under optimal conditions (A; blue arrows), exposure to environmental conditions such as 1) crowding, 2) pond drying, 3) predation, and 4) reduction in resources accelerate development (short red arrows) in prometamorphic larvae (B), but have inhibitory effects on growth and further development (long orange arrows) in premetamorphic larvae (C). The dynamic relationship between environmental variables and larval development are believed to be mediated via endocrinological changes that have different effects in pre- vs. pro-metamorphic larvae.
Figure drawing by Brandon P. Staub. Figure from Rowe, Hopkins, and Bridges. In Press. “Physiological Ecology of Amphibians in Relation to Susceptibility to Natural and Anthropogenic Factors” In The global decline of amphibians: An integrated analysis of multiple stressor effects. Eds Linder, G., Crest, S., Sparling, D. SETAC Press, Pensacola.
Highlighted amphibian research:
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