Ocorrência e distribuição espacial e temporal das larvas de anuros (Amphibia) em diferentes sistemas aquáticos da Ilha Grande (Rio de Janeiro)

Abstract

Tadpoles can be found in a number of different aquatic habitats, ranging from relatively simple predictable ecosystems such as bromeliad tank and temporary ponds, to permanent complex ecosystems like streams and rivers. Knowing about the interactions between biotic and abiotic within these habitats is crucial to understand how tadpole communities are structured. Understanding how these factors work and its importance leads to better discerning of what seems positively or negatively influence the establishment of tadpoles in their different environments. Initially, we provide a detailed discussion of the importance of these factors. Next, we evaluate the structure of the assembly of the tadpoles and their strategy of spatial and temporal occupancy in relation to the use of different aquatic systems, temporary and permanent (puddles, flooded land, streams and artificial environments) in an Atlantic Forest area in Ilha Grande (Rio de Janeiro). Subsequently, we propose an experiment to evaluate how tadpoles characteristic of different types of water habitats respond to adverse conditions of absence of free water. Then it is suggested an artificial key to the tadpoles of the Ilha Grande, based on the species covered in this study. Finally, we present the description of the tadpoles of Proceratophrys tupinamba, and provide information on its temporal distribution and microhabitat use. We recorded 12 species of tadpoles, which corresponded to 71% of amphibians of the Ilha Grande with exotrophic larvae in aquatic environments. The spectrum of habitats used varied consistently between species. Tadpoles of Aplastodiscus eugenioi and Scinax trapicheiroi used the greatest amount of habitat types, both with five records. Most species had their highest abundance in one or two types of water bodies where it occurred, so few of these species have been demonstrated to be generalists in the use of aquatic habitats. The highest species richness was found in temporary ponds, in intermittent streams and anthropic environment in the artificial gutter. When considered in terms of water habitats, the richest places were temporary pools, intermittent streams, permanent streams and the artificial gutter. It was not every month that a certain type of water resource maintained its maximum richness of tadpoles. We observe that the same type of water system may include species typical of lentic and lotic environments adapted to other, depending on the structure in which the water body has at that time, such as intermittent streams, for example. Among the abiotic factors measured, the pH, dissolved oxygen, the current, the width and depth of the water bodies more importantly explained the occurrence and abundance of different species of tadpoles. Therefore, we believe that ecological factors play an important role in determining the distribution of tadpoles within and among habitats that these organisms occupy. The proposed experiment showed that the survival times between covered eleven species and between individuals of different sizes in the same species varied considerably. This is suggestive that these species have different strategies to tolerate a condition of independence of free water. The factors that seemed most negative influence on survival of tadpoles were nektonics habit, small individual size, occupation of lentic and temporary habitats and nonspecialized reproductive mode. Alternatively, tadpoles with better performance in a condition of independence of free water were species comparatively large or medium size, that occupied mainly permanent lotic habitats, presented specialized reproductive modes and the tadpoles were mainly benthic. In this context, we can surmise that the tadpoles of species that use permanent environments are more resistant to the condition of independence of free water than those of ephemeral habitats. Noting with particular attention to the biodiversity of amphibians, theIlha Grande has a high concentration of endemic species. This respectable amphibian diversity in the study area is related to the canopy of Atlantic Forest and the large amounts of water bodies on the island, both temporary and permanent. The influence of these favorable conditions for amphibians in the region is also demonstrated in the diversity of reproductive modes, where 13 of the 39 reproductive modes described were noted for the amphibians of the Ilha Grande. These factors reaffirm this as one of the most important areas for biodiversity conservation of amphibians in the state of Rio de Janeiro. Comparing the description of the tadpole of Proceratophrys tupinamba with P. appendiculata, we observed some differences in the proportion of the body. Tadpoles of the species described were more abundant during the rainy season (October to March), this distribution is positively related to average monthly precipitation. The tadpoles are benthic and occur more often in lower stream portions of the creek. They were found more frequently exposed in the sand, which also represented the most microhabitat among those available in the stream studied.