A comparative study of predator-induced phenotype in tadpoles across a pond permanency gradient

Abstract

In a field survey the distribution of pond-breeding anuran species and their potential large predators was investigated along a freshwater habitat gradient, ranging from ephemeral pools to permanent ponds. In a laboratory experiment predator-induced plasticity was examined for all tadpole species to test whether the plastic response of ephemeral and temporary pond species differs from that of permanent pond species. Desiccation and predation pose conflicting demands; reduced activity lowers the risk of death by predation but increases the risk of death by desiccation. It was expected that species from time-constrained habitats would display a morphotype that would reduce vulnerability to invertebrate predators, thus allowing these species to maintain a high level of activity, whereas species from permanent ponds would avoid predation both morphologically and behaviourally. Species distribution and predator composition along the hydroperiod gradient differed. Variations between ephemeral and temporary ponds can be attributed to hydroperiod differences and the presence of large invertebrate predators in temporary ponds, whereas the contrasts between temporary and permanent ponds can only be attributed to the hydroperiod, since the presence and abundance of top predators are similar in both habitat types. With the exception of bufonids, all species showed predator-induced plasticity in agreement with previous studies. Tadpole species differed in the integration of the phenotypic traits measured, but differences observed between species could not be attributed only to habitat. Species from temporary habitats showed an expected response, with a low reduction of activity in comparison with the rest of the species. The lack of general patterns in the morphological changes suggests that species within the same habitat type did not converge on similar phenotypes, perhaps due to functional constraints on differences in microhabitat use in the water column.