A growing body of evidence suggests that a number of amphibian populations have declined in recent years. The cause of these population declines has been difficult to establish because in some instances only a single species is declining while sympatric species are thriving. This chapter discusses the results of research that has been conducted to determine the degree of variation present in amphibians with respect to their response to insecticide exposure. The study assessed the degree of variation in response to an anthropogenic stressor among and within species of frogs in the family Ranidae, focusing on the variation in tolerance of tadpoles to the insecticide carbaryl. Carbaryl acts by inhibiting nervous system acetylcholinesterase, which is a common mode of action among insecticides; thus, carbaryl can serve as a model chemical with which to examine amphibian responses. The study also analyzed variation in a hierarchical fashion to identify where variation was the greatest: among nine ranid species, among populations within a single species, and within populations of southern leopard frogs.
