Phenotypic Design, Plasticity, and Ecological Performance in Two Tadpole Species

This study relates community ecology to phenotypic design in two species of hylid tadpole that share larval habitat on the rocky shoreline of Isle Royale, Michigan. The ecological results indicate that the two species partition a competition-predation gradient on the shore. Pseudacris crucifer is mostly high on the shore at low density in persistent pools with predators (dragonfly larvae, Aeshna juncea); tadpoles have low individual growth rates and metamorphose late at large body size. Pseudacris triseriata is more variable in growth and development but typically grows more rapidly and metamorphoses earlier. All P. crucifer that attain metamorphosis emerge from pools with Aeshna, whereas P. triseriata metamorphose from a mixture of pools with and without predators. A reciprocal transplant experiment showed that both species survived poorly in the upper level pools with predators, which indicates that predation is more important there. The experiment did not show strong competition between the two species in either kind of pool. The phenotypes, including plasticity, of the two species are consistent with their ecological differences. Pseudacris triseriata has traits that functional arguments suggest should assist in processing food: in natural populations it hatches at large size, feeds actively and conspicuously, and has a relatively round body and small tail muscle and tail fin. Pseudacris crucifer has the opposite suite of characters, which functional arguments suggest favor predator avoidance. The variation in larval habitat correlated with differences in plasticity. In the transplant experiment, P. crucifer showed little change in phenotype, whereas P. triseriata reduced activity and increased tail fin and tail muscle size in the presence of Aeshna. This study illustrates that ecological differences in tadpoles correlate with behavioral and morphological phenotypes and that phenotypic traits can be used to predict ecological performance in manipulative experiments in natural settings.