The high diversity of amphibians in the central Amazon Rain Forest allowed us to examine the influence of tadpole antipredator defenses on assemblage structure and composition within bodies of water (α diversity) and among aquatic sites (β diversity) at a local scale. During a three-year study of tadpole assemblage composition, we found that the anuran community used a variety of bodies of water for reproduction; these ranged from streams and streamside ponds to isolated forest ponds. The distribution of several tadpole species was negatively related to fish density, while other species coexisted with high densities of fish. Tadpole size did not ensure survival against fish, and few tadpoles avoided fish by hiding in the leaf litter. Controlled predation experiments using a single tadpole species in a no-choice situation were conducted over 24- to 48-hour periods. Nearly all species of tadpoles that occurred in habitats with high fish densities were unpalatable to fish (except Centrolenella oyampiensis), indicating that unpalatability is a major adaptation allowing tadpoles and fish to coexist in this system. Unpalatability (to fish), however, was not an effective antipredator defense against odonate larvae, the other major tadpole predator in this system. The combination of predation pressure and the antipredator traits exhibited by individual species largely determined the composition of tadpole assemblages in individual bodies of water (α diversity). The heterogeneous distribution of predators among bodies water and the diversity of antipredator defenses exhibited by larval amphibians facilitated high diversity in this community (β diversity).