Assistant Professor University of California, Riverside Riverside, CA, United States
While the theory of ecological communities has allowed ecologists to generalize across different scales, major gaps remain in our understanding of how speciation, dispersal, niche selection, and ecological drift interact to create spatial variation in biodiversity (β-diversity) across trophic levels (e.g., plant, pollinators, microbes). Specifically, the extent to which the assembly of vertical communities is driven by local-scale processes, regional-scale processes, or the interplay between them remains unresolved. One path forward is to examine the extent to which species pool functional diversity mediates assembly processes of interacting communities at different trophic levels. Here we examined patterns of β-diversity across three sites that differed in regional species-pool functional diversity (SPFD) to partition the relative importance of local- and regional-scale processes on the assembly of bees and in their associated gut microbiome communities. Across three islands of the Channel Islands Archipelago in California, we sampled bee communities at 60 locations on each island and used next generation sequencing of the 16S rRNA gene to survey the bacterial community associated with the collected bees. We used a null-modeling approach to examine how local environmental conditions and species-pool functional diversity jointly influence patterns of beta-diversity of both bees and microbes.
The three islands varied in environmental conditions, β-diversity, and species-pool functional diversity. Bee β-diversity was lowest at the site with the lowest species pool functional diversity and highest on the islands with greater species pool functional diversity, suggesting that increased SPFD may increase opportunities for species sorting along environmental gradients. Our results highlight how different community assembly processes may vary in their relative importance given differences in species pool functional diversity as well as the type of organism studied (macro vs micro). This mismatch between trophic levels suggests that generalization among trophic levels may not be straightforward and that an integrative approach that considers the functional diversity of multiple trophic levels can help resolve how contemporary and historical processes act in natural communities.