Revealing beta diversity patterns of breeding bird and lizard communities on inundated land-bridge islands by separating the turnover and nestedness components
Beta diversity describes changes in species composition among sites in a region that has particular relevance for potential applications in conservation planning in fragmented habitats. However, it is difficult to reveal the mechanisms and develop specific conservation strategies if broad sense beta-diversity indices (i.e. yielding identical values under nestedness and species replacement) are used. Partitioning beta diversity into turnover (caused by species replacement from site to site) and nestedness-resultant components (caused by nested species losses) could provide a unique way to understand the variation of species composition in fragmented habitats.
Here, we collected long-term occupancy data of breeding birds and lizards on islands in an inundated lake in China. We decomposed beta diversity of breeding bird and lizard communities into spatial turnover and nestedness-resultant components to assess their relative contributions and respective relationships to differences in island area, isolation, and habitat richness.
Our results showed that spatial turnover contributed more to beta diversity than the nestedness-resultant component. The degree of isolation had no significant effect on total beta diversity or their components, neither for breeding birds nor for lizards. In turn, in both groups the nestedness-resultant component increased with larger differences in island area and habitat richness, respectively, while turnover component decreased with them. The major difference among birds and lizards was a higher relevance of nestedness-resultant dissimilarity in lizards, suggesting that they are more prone to local extinctions derived from habitat fragmentation. Despite the existence of some nested patterns, according to the dominance of the spatial turnover component of beta diversity, we suggest that all islands have potential values of biodiversity conservation and deserve protection for breeding bird and lizard communities.