Competition and the distribution of spring peeper larvae

Studies of tadpole distributions have shown that despite overlapping affinities for semipermanent and permanent ponds, distributions of the spring peeper (Pseudacris crucifer) and the green frog (Rana clamitans) tend to be nonoverlapping. Because spring peepers are believed to be poor competitors, I hypothesized that competition from green frog larvae limits the distribution of spring peeper larvae. I stocked field enclosures with a constant density of spring peeper larvae, and one of four densities of green frog larvae (a "target-neighbor" design). Increased green frog density had a small effect on metamorphic size and no effects on survivorship, larval period or growth rates of spring peepers. In contrast to these small interspecific effects, green frogs had a large effect on their own performance. Intraspecific competition resulted in a 50% decline in growth rate and an 11% decline in metamorphic size. These results suggest that the species are segregated in resource use, or that compared with green frogs, spring peepers are better able to cope with depressed resource densities. In either case, this field experiment provides no evidence that interspecific competition from green frogs limits distributions of spring peepers. Other factors such as predation and breeding site choice by adults may contribute to the absence of spring peeper larvae from many semipermanent and permanent ponds.