Simulation-based insights into community uniqueness within fragmented landscapes

Context Local contribution to beta-diversity (LCBD) assesses community composition uniqueness of sites within a region. While it is useful to identify sites with exceptional species composition and, thus, prioritize conservation actions, it is unclear what determines community uniqueness in patchy habitats. Objectives The goal of this study was to clarify the processes underlying community uniqueness in fragmented landscapes and understand how habitat characteristics and community characteristics affect this beta-based diversity indicator. Methods We simulated neutral metacommunities and used a variance-based method to assess the contribution of each habitat patch to total beta-diversity, both in terms of replacement and abundance difference. Then, we analyzed the effects of patch and metacommunity characteristics on LCBD. Results Community uniqueness in species replacement and richness/abundance differences responded differently to community and patch features. Patch quality was the habitat attribute with the strongest effects on all community uniqueness aspects, leading to singular assemblages with high species richness and abundance of rare species. While patch connectivity promoted singular assemblages with high richness, patch size increased community uniqueness in species replacement over time, favoring assemblages with high abundances of rare species. Conclusions Community uniqueness in species replacement and richness/abundance differences convey different information and should be considered separately to propose adequate conservation strategies. Habitat quality emerged as a critical factor in shaping beta-diversity, suggesting that it should be a primary focus of conservation efforts. Future studies are needed to evaluate the generality of our results in different spatial and ecological contexts.