Biogeografia de ilhas na Amazônia: investigando a biodiversidade de um arquipélago fluvial amazônico usando aranhas como organismos modelo

Abstract

Islands around the world are considered natural laboratories, occurring in many different ecological contexts such as oceanic, fluvial islands or even similar environments such as hydroelectric lakes or forest fragments. Such islands and similar environments are usually approached as indivisible units in biogeographic studies, that is, the physical limits of the island would represent the theoretical limits of the assemblies, even on large islands. In addition, the contribution of island environments to regional biodiversity remains largely unexplored, especially in tropical regions. For animals such as arthropods, it is possible that the processes that govern patterns of abundance, diversity and composition occur on a local scale, with interactions between organisms. Therefore, understanding the influence that the size of the island has on the assemblages in a smaller or grain area within this island is essential for more accurate interpretations of the ecological processes that occur in the assemblages of arthropods. In this study we investigated the effects of the size of the islands on the abundance, alpha diversity, dominance and composition of arboreal spiders (chapter 1), we also investigated the patterns of local diversity, abundance and composition of arboreal spiders, with comparisons between island and continuous environments ( chapter 2) on one of the largest sets of river islands in the world in the Anavilhanas National Park and surroundings, located on the lower course of the Rio Negro. We selected 30 islands in the archipelago and another 23 sites in areas of continuous forest (igapó and terra firma forests). We collected the spiders using a technique of vigorously shaking the vegetation in a standardized time of 30 minutes at each sampling point. The assemblies were accessed using data of abundance, richness and composition of species / morpho-species, as well as the Simpson and Alpha Fisher diversity indexes calculated with the statistical software R. We relate the alpha diversity, abundance, dominance and composition with the area of ​​the islands with linear regressions, loess curves, piecewise models and proportion analysis by species. A total of 4905 spiders were collected between the fluvial islands (3278 individuals), igapó forests (942) and terra firma forests (685). We identified 290 species / morphospecies among the 1404 adult individuals. We observed the influence of the area on alpha diversity for islands with an area between 0.01 to 0.1 km2, however for larger islands there was no relationship. Indicating that for arboreal spiders of a certain size, the island would be large enough that the total diversity of the island has little influence on the local number of species. We observed greater dominance in the small islands, indicating that the area would also have effects on the equitability of the species, with a pattern similar to that observed in the analysis of alpha diversity, where there is greater dominance on islands with a smaller area and no relationship on larger islands. There was no influence of the island area on the proportions of individuals per species or on the composition of species. The average number of species was similar between environments, ranging from 14.4 to 16.8 species per site. However, the alpha diversity represented by the Fisher's alpha index was greater in upland forests compared to other environments. The rarefaction curves also suggest that the marginal environments (igapó and terra terra forests) have a greater total number of species than the fluvial islands. The species composition was different between the island and non-island environments with few shared species, the river islands have 12 species in common with the igapó forests and only five with the upland forests. The ordering (NMDS) and similarity analysis (ANOSIM) revealed that the composition of spider species is significantly different. Only 11 of the 290 identified species were recorded in all sampled environments.