Bat community assembly in the ecotone of two neotropical biodiversity hotspots is determined by environmental filtering rather than historical factors.

Ecotones between major biomes represent strong ecological gradients and offer valuable opportunities to investigate the processes structuring biological communities. The ecotone between the Cerrado and the Atlantic Forest is one of the most extensive and biodiverse transition zones in South America. Here, we investigated the assembly processes of bat communities across the Cerrado-Atlantic Forest ecotone, contrasting the predictions of environmental filtering, competitive exclusion, and neutral assembly using a coevolutionary community assembly framework. We also evaluated how environmental and historical variables influence patterns of phylogenetic beta diversity and tested whether abrupt changes in community composition occur along the gradient from the ecotone towards the core areas of both biomes. We found that environmental filtering was better supported than competitive exclusion and neutral models in structuring bat communities within the ecotone. Variation in phylogenetic beta diversity was primarily explained by environmental variables, particularly precipitation seasonality, annual precipitation, annual temperature range, and canopy height. An abrupt change in phylogenetic beta diversity was detected from the ecotone towards the core of the Cerrado biome, whereas no comparable shift was observed towards the Atlantic Forest, indicating that distinct assembly processes operate along gradients associated with these two megadiverse biomes. Our results highlight the dominant role of environmental filtering in shaping bat communities in the Cerrado-Atlantic Forest ecotone and emphasise the importance of accounting for coevolutionary processes when interpreting community assembly patterns in Neotropical biodiversity hotspots.