Small-bodied Mammal Diversity Facets Vary Discretely Across an Understudied Ecotone in the Western Amazon-Cerrado

Tropical forests and savannahs worldwide are yielding to agribusiness, impacting biodiversity. In the southern Amazon deforestation arc , deforestation progress and limited study of extensive areas result in knowledge gaps on the impacts on biodiversity. We examined patterns of small-bodied mammal species diversity along a gradient ranging from closed-canopy to open-area savannahs, in the Guaporé river basin, Brazil. During one temporal replica—between December 2011 and October 2012—we sampled small mammals using live-traps in seven sites along three 1 km transects each. We assessed and predicted species alpha-diversity (within site), beta-diversity (unshared between sites), and zeta-diversity (shared) across the gradient, relating each biodiversity facets to the sites habitat structure, including vegetation height and above-ground biomass. From 202 individuals recorded, we uncovered 18 species in the region, whereas alpha-diversity was similar between sites, the species composition discretely shifted from non-floodable terra firme to open-areas of the transition zone southwards. Sites located at the intermediary zones of the north–south axis had lower beta-diversity contributions in comparison with northern- and southernmost sites, suggesting mixed biome influences. Zeta-diversity declined rapidly from closer sites to the more distant ones. Along the middle Guaporé basin, small mammal distribution correspondingly reflected the influence of the Cerrado and Amazon. Species presence—and cryptic diversity in terms of species not recorded yet—highlights conserving extensive habitats to accommodate diverse regional-local diversity needs, whereas both beta- and zeta-diversity patterns reveal that sites distinctiveness and multiple assemblages are required to safeguard the regional-scale diversity.