Dung beetles maintain phylogenetic divergence but functional convergence across a highly fragmented tropical landscape.
Understanding how human-modified landscapes affect the phylogenetic composition and assembly mechanisms of biological communities is critical for effectively managing and restoring tropical ecosystems. We evaluated how forest coverage loss, fragmentation and landscape heterogeneity affect the phylogenetic diversity of dung beetles and their assembly mechanisms in Los Tuxtlas Biosphere Reserve, a protected but highly fragmented tropical landscape. We calculated Faith's phylogenetic diversity, mean pairwise phylogenetic distance and mean nearest taxon distance for 5,388 individuals in 36 species. The standardised effect sizes of these metrics were estimated to control their correlation with species richness. Phylogenetic diversity was also assessed separately for each dung beetle functional group. Finally, we compared the mean functional and phylogenetic pairwise distance and mean nearest taxon distance and measured the phylogenetic signal among dung beetle functional traits to determine the influence of niche conservatism on the phylogenetic structure of species assemblages. Faith's phylogenetic diversity of dung beetles was positively correlated with forest coverage, while their mean phylogenetic and nearest taxon distance values decreased with increasing landscape fragmentation. Necrophagous beetles and forest specialists responded most negatively to forest coverage loss and fragmentation. Alpha and beta diversity values showed phylogenetic overdispersion but functional convergence and weak phylogenetic signals in their functional traits, suggesting low niche conservatism. Landscapes with moderate forest coverage (≥40%) favoured higher phylogenetic beta diversity, whereas phylogenetic and functional beta diversity decreased significantly in landscapes with low forest coverage (<30%). Synthesis and applications. Forest habitats in fragmented landscapes are essential for safeguarding the evolutionary history of dung beetles, reducing biotic homogenisation processes by favouring phylogenetic overdispersion and complementarity between sites. Therefore, to secure the phylogenetic diversity of dung beetles within fragmented tropical reserves, we recommend protecting the existing forests, preventing further fragmentation of continuous forest areas and increasing matrix quality by implementing biodiversity-friendly production systems. Finally, managers should consider assessing different functional groups in other species, as their response to landscape disturbance may not be phylogenetically similar. The above will allow more effective management practices to protect the species most susceptible to disturbances.