Asymmetric competition between Rana clamitans and Hyla versicolor tadpoles

Abstract

When two organisms interact over a potentially limiting resource, several outcomes are possible (e.g. neither affected, both equally affected, one affected more than the other). The outcome depends on a variety of factors, both internal and external to the organism. We performed a laboratory experiment to investigate the outcome of potential competitive interactions between tadpoles of the green frog (Rana clamitans) and the gray treefrog (Hyla versicolor), and to examine the factors that may explain the outcome of the interaction. We found that competition between these two species was asymmetric. Hylaversicolor tadpoles were more affected by intraspecific competition than interspecific competition (i.e. grew faster when grown with heterospecifics than conspecifics); whereas, R. clamitans tadpoles were more affected by interspecific competition than intraspecific competition (i.e. grew faster when grown with conspecifics than heterospecifics). Based on behavioral observations, this result could not be explained on the basis of activity levels, a trait previously linked to competitive ability in tadpoles. However, differences in initial body size may help explain the observed results; the gray treefrog tadpoles were larger than the green frog tadpoles.