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Diversity and nestedness in bat assemblages in a mosaic of four Amazonian natural habitats
The Amazon biome is made up of a mosaic of different habitats, with continuous terra firme forest interspersed with other types of forest (e.g., mata de igapó) and non-forest habitats (e.g., campinas), that together represent 35% of the area of the biome. This mosaic of different habitats helps to sustain a rich and abundant flora and fauna, making the Amazon one of the most biodiverse regions in the world. In this study, we use data on bats collected in four Amazonian habitats (continuous forest, natural forest patches, campinarana and savannah), and use both additive partitioning and metacommunity nestedness analysis to: (i) determine to what extent the bat assemblages show metacommunity nestedness, and (ii) compare the functional, taxonomic, α and β-diversity (β-diversity total and its components - turnover and richness difference) between the habitat types. Our hypothesis was that the bat assemblages in forest patches, campinarana and savannah would be subgroups of the assemblage found in the continuous forest. In addition, we expected that the assemblages in savannah and campinarana would be nested within the assemblage in forest patches. We further hypothesised that the continuous forest would have greater taxonomic and alpha diversity than the other habitats, and that beta diversity would be lower between forest and forest patches, and higher between forest and both campinarana and savannah. Finally, we tested the hypothesis that the composition of functional traits would vary along a gradient from continuous forest, to forest patches, to campinarana, to savannah. To test these hypotheses, we used data collected between 2009 and 2018, in the north of the Brazilian Amazon. Bats had been captured using mist nets in sites in each of the four habitat types. Based on our data (3,686 captures), forest and forest patches (forest habitats) showed higher α-diversity than savannah and campinarana (non-forest habitats). The data supported our hypothesis that forest patches, campinarana and savannah are nested in continuous forest, that is, they are subgroups of the continuous forest. The data also showed a gradient in functional β-diversity, with continuous forest having a low value compared to forest patches, intermediate in comparison with campinarana and high when compared with savannah. Overall, these results indicate that the beta-diversity between campinarana, savannah and continuous forest and forest patches is driven more by the absence of some species in campinarana and savannah that are present in the other habitats than by species turnover. In terms of functional traits, animalivorous bats were more associated with forest and forest patches, while phytophagous bats were more associated with savannahs and campinaranas. Differences were also found in relation to vertical stratification, where bats that use the canopy in the forest were more captured at ground level in the savannah, forest patches and campinarana than those species which use the understorey of the continuous forest. Our results bring new understanding to the distribution and composition of bat assemblages along natural habitat gradients in the Amazon, with important implications for both ecology and conservation of these species and habitats.
Amazonian savannahs; α-diversity; β-diversity; campinarana; forest patches; phyllostomid bats; white-sand ecosystems
William Douglas Carvalho, Fábio Zanella Farneda, Isaí Jorge Castro, Ana Carolina Martins, Bruna Silva Xavier, João David Miguel, Karen Mustin, Renato Richard Hilário, José Júlio Toledo