DISTRIBUTION OF TADPOLES WITHIN AND AMONG BRAZILIAN STREAMS: THE INFLUENCE OF PREDATORS, HABITAT SIZE AND HETEROGENEITY

Abstract

We studied the composition and richness of local tadpole assemblages in several streams at a forest site in southeastern Brazil. We initially focused on species distributions within streams, comparing the relative availability of microhabitats with the relative use of each microhabitat type by tadpoles of different species, in order to assess the existence of preference patterns. Then we assessed the role of features assumed to influence species distributions among streams, which may influence breeding site selection by adult frogs and, consequently, tadpole distribution. These features were stream size, tadpole predator abundance, structure of marginal vegetation, and microhabitat availability for tadpoles. We looked for gradients of species richness along gradients of the variables noticed to influence tadpole assemblage composition. Tadpoles of all species showed selectivity in microhabitat use. Species distribution among streams was influenced mostly by number of potential tadpole predators present, stream volume, arboreal vegetation cover at stream margins, and tadpole microhabitat diversity, though only the first two variables accounted for gradients in species richness. Even though smaller streams tend to shelter more anuran species than larger ones at sites in southeastern Brazil, we recommend the conservation of streams of a range of sizes and structural features, since anuran assemblages associated with streams vary in species composition along gradients in these characteristics.