Fluctuations in Prey Availability and Food Limitation for a Terrestrial Salamander

Jaeger

A Virginia population of the forest-dwelling salamanderPlelhodon cinereus was repeatedly sampled over four years to determinevolume and number of prey ingested under varying conditionsof moisture and temperature. The proportion of the populationon a daily negative energy budget was estimated by comparingactual foraging success with laboratory determined values of energeticrequirements at various temperatures.Prey became "limited" in availability during rainless periods,apparently because salamanders were not able to forage in dryleaf litter. Foraging success increased with increasing rainfall.Food was a "limiting" resource for a majority of the populationon most sampling days, as determined by energy budget analysis.While ambient moisture regulated food availability, ambient temperatureset the metabolic requirements and assimilation efficienciesfor the population. Consequently, food was more limitingon dry, warm days and less so on wet, cool days. These datasupport the hypothesis that intraspecific competition frequentlyoccurs for a food resource that is periodically limited in availability.resource (Jaeger, 1974a; Fraser, 1976a; Thurow. 1976: Kaplan,1977; Jaeger and Gergits, 1979).Interspecific competition for food is widely considered to bea dominant factor in determining species diversity in terrestrialcommunities (e.g., see several papers in Cody and Diamond. 1975).Studies of terrestrial salamander communities (Jaeger. 1974b;Fraser, 1976b) have provided some of the empirical evidence insupport of this theory. Consequently, it is important to reexaminethe current debate concerning the mechanism of competitionamong salamanders: is it for food, space, or both? In the presentpaper I offer additional data, from a seven year study, in supportof the hypothesis of food competition and I suggest that interferencecompetition for space may be a mechanism for defendingforaging areas.The data presented here are of two types. A field study providedinformation on the foraging success of a population ofP. cinereus in a natural habitat under various conditions of moistureand temperature. A laboratory study then yielded estimatesof the energetic requirements of P. cinereus at various temperatures.Interfacing the two data sets allows a test of the hypothesisthat food is a periodically limiting resource for the red-backedsalamander.

Fluctuations in Prey Availability and Food Limitation for a Terrestrial Salamander

Series