How useful is island biogeography for predicting the impacts of habitat isolation on plant communities?

Background/Question/Methods

The theory of island biogeography laid the foundation for predicting and testing the impacts of habitat loss and fragmentation as well as conservation reserve design.  Yet, the appropriateness of this classic theory for predicting species richness patterns in spatially-structured terrestrial landscapes has been questioned for many reasons, including the difficulty in delineating suitable habitat patch boundaries, the fact that matrix habitat may not be inhospitable, and that systems may not be in equilibrium. Nonetheless, island biogeography continues to be used as a theoretical framework for predicting the impacts of habitat loss and fragmentation, in part, because of its simplicity. Here, we assess the utility of island biogeography theory for predicting species richness patterns and colonization and extinction dynamics in a long-term replicated landscape experiment designed to test for patch isolation.

Results/Conclusions

In our experimental landscapes, connectivity has increased plant species richness over time. After twelve years, plant species richness is 20% higher in connected vs. unconnected patches and some species are significantly more abundant on connected than unconnected patches. For common species, these changes in abundance result from decreased extinction rates (and presumably rescue effects) in connected patches rather than increased colonization rates. However, in our successional system, the relative importance of colonization and extinction rates changes over time and the equilibrium assumptions of island biogeography are challenged. The spatial and temporal scales of organism movement relative to the spatial and temporal scale of suitable habitat on the landscape will be critical for predicting species richness dynamics over time.