Predator-Prey Interactions in the San Marcos Salamander (Eurycea nana): Predator Generalization and Stress Hormones in Response to Introduced Predators
MetadataShow full metadata
Predation is a strong, influential force in most ecological communities. Inappropriately responding to predators typically results in the direct consumption of prey individuals. In addition to responding appropriately to predators in order to survive these encounters, prey individuals are under selection to minimize the costs associated with responding. These costs may reduce the overall fitness of prey individuals as time spent responding to predators is time not spent increasing fitness through activities such as foraging or reproducing. As such, prey individuals should optimize their responses in order to survive encounters with potential predators as well as to minimize the costs associated antipredator behaviors.
The introduction of novel predators into many environments has contributed to the decline in amphibian populations. Often, amphibians lack the ability to recognize these novel predators, and therefore, either do not respond or respond inappropriately to them. One such species which may be negatively affected by introduced predators is the San Marcos salamander (Eurycea nana). Eurycea nana is a federally threatened, fully aquatic salamander endemic to the headwaters of the San Marcos River. Currently, a diverse assemblage of native and introduced fish predators is present in the San Marcos River. While prior studies have helped to understand some aspects of how these salamanders respond to native and introduced predators, the role of predator generalization has yet to be explored. I found that E. nana can generalize its response to novel predators, as long as there are still similarities between these novel predators and predators which they recognize. Additionally, I have examined a stress hormone, corticosterone, to further characterize differences in the way E. nana responds to native and introduced fish predators. Differences in the way E. nana responds to native and introduced predators suggest that introduced predators may be causing a muted or diminished response. Differences in the temporal variation in risk of predation may be driving these differences, because introduced predators are highly abundant and may be frequently encountered.