Disentangling Direct and Indirect Effects of Temporal Isolation on the Multifaceted Diversity of Small Mammals on Land-Bridge Islands

Aim

A major goal of island biogeography is to understand how island communities are assembled over time, and temporal isolation has been shown to affect species diversity. However, our knowledge of the indirect effect of temporal isolation on species diversity through other island characteristics is still limited, constraining our understanding of assembly processes on islands, particularly land-bridge islands. The purpose here was to disentangle the direct and indirect effects of temporal isolation on three dimensions of diversity (taxonomic, phylogenetic and functional diversity) of small mammals on land-bridge islands.

Location

Zhoushan Archipelago, China.

Taxon

Small mammals.

Methods

We performed small mammal censuses on 39 land-bridge islands and a nearby mainland site. We first used univariate linear regressions to test the relationships between diversity indices of small mammals and island characteristics, and then built piecewise structural equation models (SEMs) to disentangle direct and indirect effects of temporal isolation on multifaceted diversity.

Results

In line with our expectation, temporal isolation directly affected taxonomic diversity and indirectly affected all three dimensions of diversity. The indirect effects of temporal isolation arose because young islands have larger island area and lower spatial isolation than old ones, and larger or remoter islands suffer stronger human activities, all of which affect species diversity. Importantly, the indirect effects of temporal isolation were strong for all three dimensions of diversity.

Conclusion

The diversity indices respond differently to island characteristics, with mechanisms that directly and/or indirectly relate to temporal isolation. Future studies on temporal isolation effects should attempt to quantify indirect effects rather than only direct effects. Furthermore, considering multifaceted diversity will contribute to identifying the underlying processes for community assembly and planning effective conservation strategies for species diversity.