Evolutionary mechanisms and successional dynamics of bird communities across madagascar's tropical forest

Abstract

Habitat loss is a primary driver of changes in biological communities and ecosystem functioning within fragmented landscapes. However, these effects are frequently assessed in isolation. This study examined how environmental predictors at multiple spatial scales influence the taxonomic, phylogenetic, and functional components of bird assemblages. Data were collected from 240 point-count stations across three forest types in the Antananarivo highlands of Madagascar: old-growth, primary, and secondary forests, using a robust multi-model framework. Multi-dimensional diversity was quantified through taxonomic structure, 13 functional traits representing morphology, diet, and lifestyle, and phylogenetic history. Although non-endemic species exhibited compositional overlap across habitats, assemblages in secondary forests experienced significant deficits in taxonomic richness, functional richness (FRic), functional dispersion (FDis), and phylogenetic diversity (PD) compared to old-growth reference sites. This pronounced multi-dimensional biodiversity loss was primarily attributed to the decline of endemic species in modified habitats. Environmental variables at different spatial scales differentially influenced these diversity dimensions: taxonomic diversity was strongly associated with local vegetation structural complexity, such as maximum tree height and tree species richness, while functional and phylogenetic diversity were mainly constrained by broader-scale climatic variables, including temperature seasonality, and anthropogenic disturbances, such as distance to roads. Forest degradation fundamentally alters the multi-dimensional diversity of Malagasy avifauna, resulting in a substantial loss of endemic evolutionary history and functional trait space. These findings indicate that the most effective forest management strategy for maintaining the evolutionary and functional integrity of these unique bird assemblages is the strict preservation of old-growth reference sites that retain critical vertical vegetation structure, in conjunction with efforts to reduce anthropogenic isolation in degraded landscapes.