TESTS OF FUNCTIONAL EQUIVALENCE - COMPLEMENTARY ROLES OF SALAMANDERS AND FISH IN COMMUNITY ORGANIZATION

We experimentally tested whether two similarly sized generalist predat ors found in different habitats had similar effects on prey community patterns. Notophthalmus viridescens (the red-spotted newt) occurs prim arily in temporary ponds, while Enneacanthus obesus (the banded sunfis h) is restricted to permanent ponds. Larval anurans are an important p rey assemblage found in both kinds of ponds. We stocked both predators in artificial ponds together with six species of larval anurans, form ing different species assemblages, to assess whether a similar abundan ce and biomass of each predator would have comparable impacts on commu nity patterns. The predators differed in their effects on prey species composition but had similar impacts on composite community attributes , including prey species diversity and total prey biomass. Enneacanthu s eliminated Pseudacris crucifer, Hyla andersonii, Hyla versicolor, an d Scaphiopus holbrookii, creating a community dominated by Bufo woodho usii and Rana sphenocephala. Notophthalmus eliminated Bufo, creating a n assemblage dominated by Pseudacris but also containing four addition al species. Very few anurans survived in ponds containing both newts a nd fish. The different consequences of predation by newts and fish ref lect different effectiveness of anuran antipredator defenses against t hese predators. Mechanisms that reduced predation by fish, such as unp alatability, were ineffective against newts. Our findings suggest that a patchy distribution of functionally distinct predators across a lan dscape of discrete habitats will contribute to predictable patterns of spatial variation in community composition and will create a mosaic o f communities dominated by different prey species.