Variations in environmental conditions along gradients play an important role in species distribution through environmental filtering of morphological and physiological traits; however, their effects on bat diversity remain poorly understood. Here, we investigate the effect of the distance to the nearest watercourse, terrain elevation, vegetation clutter, basal area and canopy height on taxonomic, functional and phylogenetic diversity and on the predominance of some functional traits (body mass, wing morphology and trophic level) of bat assemblages (phyllostomid and mormoopid bats) in a terra firme forest, in the northeastern Brazilian Amazon. We captured bats using mist nets in 15 permanent plots over a 25 km2 area of continuous forest. We captured 279 individuals belonging to 28 species with a total of 77.760 m2.h of sampling effort. Our results showed that bat richness increases as a function of distance to the nearest watercourse and that the assemblage also changes, with more diverse taxonomic and functional groups in areas further from the watercourse. Furthermore, elevation positively affects species richness, and the basal area of the forest positively influences the average body mass of bats. Taken together, our results demonstrate that subtle variations in the environmental conditions along a local scale gradient impact on the main dimensions of bat diversity in primary forests.

Drivers of forest structure in central African rain forests are largely unknown. Using forest inventory data (3024 0.4-ha plots) in a forest concession of 154 456 ha in north-eastern Gabon covering an altitudinal gradient (from 485 to 1009 m asl), relationships between above-ground plot biomass and environmental variables (soil type, altitude, slope, aspect) and floristic composition (score given by an ordination method) were tested. After controlling for confounding variables, biomass was significantly related to altitude (with a modal response peaking at 346 Mg ha–1 on western slopes at an altitude of 707 m asl) and to aspect (additional 18.3 Mg ha–1 on eastern slopes) but not to floristic composition. Biomass and basal area responded differentially to the environment. Mean wood density was significantly related to soil, altitude and floristic composition, with a predicted minimum of 0.60 g cm–3 at an altitude of 1009 m asl in stands characterized by Scorodophloeus zenkeri and a maximum of 0.69 g cm–3 at an altitude of 458 m asl in monodominant Gilbertiodendron dewevrei stands. Variation in forest structure in the concession was primarily driven by altitude while floristic composition played a role in differentiating the variation in biomass and basal area.