Influência de fatores bióticos e abióticos na distribuição temporal e espacial de girinos de comunidades de poças temporárias em 64 km2 de floresta de terra firme na Amazônia central

Abstract

The objective of this study was to evaluate the distribution of anuran species larvae and their relationships with biotic and abiotic factors in 136 ponds, distributed in 31 plots, across the 64 km2-Reserva Florestal Adolpho Ducke (RFAD), Manaus, AM. We estimated water-body availability in 432 hectares by walking a system of 18, 8-km trails and quantified all water bodies present within 15 meters from each side of the trail. We evaluated compositional differences among isolated and streamside ponds by collecting tadpoles from the water bodies. Streamside ponds were by far the most common type of water body encountered on our trail system, representing over 90 % of the ponds. The ponds available in RFAD are characteristic of areas near streams in terra firme forest and are important resources for amphibians. We calculated differences in tadpole species composition among and within rainy seasons, the rate of change of predator species composition, and tadpole abundance and pond area from the sample X to X + 1 successively, using Euclidean distances. This measurement was used to evaluate differences in tadpole distributions between rainy seasons and in relation to the rate of change of the abiotic (pond area) and biotic (predators) factors with rate of changes in tadpole distribution. The temporal variability and stability of tadpole communities differed within the period sampled. The tadpole community of the first period (2002/2003) underwent a directional change, probably caused by predation pressure and changes in the reproductive phenology of some species. The second period (2003/2004) presented a non-linear pattern (light tendency of directional change in the initial samples tending towards a convergence in the final samples) possibly caused by climatic conditions that may increase temporary heterogeneity in some dynamic systems, such as water bodies. In the third period (2004/2005) we found a stochastic pattern, in spite of the overall tendency towards directional change. The global tadpole community analysis showed a subtle pattern of directional change, with stochastic effects in population fluctuations. The rate of change in tadpole species composition was correlated with the rate of change of predator species composition between the first and third periods sampled. Changes in the distribution of tadpole predators have been demonstrated in several studies. The pattern of co-occurrence of the tadpole species, considering the structure of the plots, was deterministic. Stream width influenced the largest community pattern, due to a large number of species being correlated with larger ponds that generally form beside large streams. In ponds, tadpole species composition based on presence-absence data was influenced by pond area. Species as Phyllomedusa bicolor, P. vaillanti and Hypsiboas geographicus survive in large ponds and with a hydroperiod longer than five months. Tadpole species composition and abundance data didn't differ among the drainage basins (meso-scale). However, the species composition was different among micro-drainage basins (micro-scale), indicating that species can respond individually to habitat or pluviometric regime and tend to reproduce in sites with certain abiotic attributes. In RFAD, the abiotic factors function as a filter influencing tadpole communities. However, a more general vision about the factors that influence tadpole distribution in streamside ponds is necessary to evaluate the distribution of adults and predators inside ponds and plots, because strong negative relationships exist between fish species richness and proximity of ponds to a stream. Simultaneous, long-term studies at different scales are necessary to understand the processes that operate in the macro (landscape), meso (regional) and micro-scale (local) and, consequently, to understand species’ distributions.