A matter of distance: Native bee lineages and diversity in fragmented landscapes

Insects embody Earth’s greatest evolutionary experiment in diversity, yet we still know little about how their ecological and evolutionary dimensions shift through time in response to climate change and land-use change. Native bees, key pollinators in many ecosystems, are especially sensitive to habitat fragmentation and land-use change. We draw on a dataset spanning 13 years (2011–2024) encompassing surveys in seven years from coastal southern California, a biodiversity hotspot, to quantify evolutionary relationships among the 261 bee species recorded. We reconstructed a near-complete, species-level phylogeny by integrating the Henríquez-Piskulich et al. (2024) supermatrix with newly generated and publicly available COI barcodes under a constrained maximum-likelihood framework. Linear mixed models revealed that phylogenetic diversity (PD) was higher in reserves than in fragments and varied among years. Functional diversity (FDis) increased with both phylogenetic diversity and taxonomic diversity and varied significantly among survey years. These metrics were correlated, indicating that taxonomic, functional, and phylogenetic diversity are interrelated but capture distinct dimensions of assemblage structure. Together, these findings show (i) that large reserves support deeper evolutionary and functional diversity compared to small fragments, and (ii) that multiple diversity metrics reveal complementary insights into bee assemblage organization. By integrating long-term monitoring with trait-based and phylogenetic data, this study provides a multidimensional framework for understanding biodiversity change in fragmented landscapes.