Distribuição das assembleias de girinos associadas a riachos da Reserva Ecológica de Guapiaçu, Cachoeiras de Macacú, Rio de Janeiro, Brasil

Abstract

Tadpoles are diverse and abundant organisms in headwater streams of tropical rainforests and constitute important components of biological, trophic and functional diversity. Furthermore, different structural (e.g. size, depth, microhabitat availability) and limnological (e.g. conductivity, temperature) characteristics affect tadpole organization. Although the larval stage is the most vulnerable in anurans, subject to high mortality rates, researches on tadpoles in the neotropics, as tools for their identification, remain scarce face the high diversity of anurans found in this region. In this thesis, I present a compilation of information on the main factors affecting tadpole assemblages in the tropics (Chapter 1), the morphological characterization of tadpoles found in streams during the study with a propose of dichotomous key of identification (Chapter 2), and evaluated the relative importance of geographical position and the temporal variation o local environmental factors on tadpole assemblages through 15 months in 10 small streams in the Atlantic Forest of Reserva Ecológica do Guapiaçu (REGUA), municipality of Cachoeiras de Macacú, Rio de Janeiro, Brazil. I also investigated the correlation between tadpoles and the environmental variables of streams (Chapter 3). We can recognize at least eigth major trends regarding the distribution and structure of tropical tadpole assemblages: (1) stream size and microhabitat diversity are important abiotic features influencing species richness and composition; (2) in ponds, the permanence gradient (e.g., hydroperiod), and the heterogeneity of habitat are the main factors modeling tropical tadpole assemblages; (3) species composition seems to be a more relevant assemblage parameter than species richness and should be first considered when planning conservation of both pond and stream-dwelling anurans; (4) predation seems to be the most important biotic interaction structuring tropical tadpole assemblages, with vertebrate predators (e.g., fishes) being more voracious in permanent habitats, while invertebrates (e.g., odonate naiads) are the most important in temporary ones; (5) tadpoles may play a regulatory effect preying upon anuran eggs and recently hatched tadpoles (6) microhabitat use varies in function of breeding habitat choice by adults, presence of predators, phylogeny, stage of development and heterogeneity of the habitat; (7) historical factors restrict the breeding habitats that species may use, and impose behavioral and physiologic constrains; (8) temporal variation in biotic (e.g., risk factors) and abiotic factors (e.g., rainfall distribution), and the reproductive patterns of the species may interfere in the structure of tropical tadpole assemblages. Future efforts regarding the study of tadpoles should contemplate assemblages associated with streams, and experimental studies. Temporal variation in the environmental heterogeneity resulted in predictability of local tadpole assemblages. The environmental component explained 23% of the variation in tadpole composition, while spatial parameters explained the smaller portion of the variation (16%). A comparatively high portion of temporal variation in the environmental heterogeneity was spatially structured (18%). The proportion of litter and rocks on the stream bottom, depth, conductivity, and temperature were correlated with tadpole composition. The gradient created by the proportion of litter and rocks represented the changes from permanent and intermittent streams. This gradient provided the species turnover, which also followed a gradient of conductivity, temperature, depth, and in a lesser proportion, hydroperiod and width, all being strongly associated with permanence of streams. The results also corroborate with both the environmental and the biotic control model and indicate that temporal variation in environmental heterogeneity and the spatial position are important to the structuring of local tadpole assemblages in the streams of REGUA. The results also allowed to distinguish between tadpoles assemblages exclusive of permanent, intermittent, and those inhabiting both streams. The results of this chapter are relevant to understand in which extension the effects of temporal variation in environmental heterogeneity and spatial processes affect the structure of tadpole assemblages, the most fragile life stage of anurans