Islands are popular model systems in ecology, biogeography, and evolutionary biology, since they represent well defined, discrete spatial entities and are regarded as natural laboratories of evolution. Island biotas have fascinated biologists for a long time and have prompted some of the most important studies and theories in ecology, biogeography, and evolutionary biology. However, the knowledge about the global scale distribution of vascular plant diversity on islands is still insufficient. Moreover, the environmental and historical determinants of diversity as well their underlying mechanism are to date heavily debated.

Results/Conclusions

Here we present a synthetic overview of global plant diversity on islands. We demonstrate that the number of plant species on an island can be reasonably well explained by a few and relatively simple abiotic characteristics (area, isolation, temperature, precipitation, topography and island geology). A multi-predictor model comprising these six variables accounts for 85% of the variation in a global set of 488 islands worldwide and also accounts for the overall lower richness of island floras. In a second step, we looked at endemism richness – a measure that combines endemism and species richness. A key result from this part of our study is that islands contribute significantly to the world’s biodiversity despite their relatively lower species densities: About 70,000 species of vascular plant species are endemic to the world’s islands – about one fourth of all species. Furthermore, our analysis reveals that island biotas are more severely threatened by human land use change than mainland regions - a finding that is consistent with different methods to assess human activity (habitat loss, human footprint). Future projections of habitat loss from the Millennium Ecosystem Assessment further suggest that habitat loss might even accelerate on islands as compared to mainland areas. We conclude that island conservation should be a top priority in global conservation efforts. Insights from ecology and biogeography might play a key role in assessing global change related biodiversity changes and in developing appropriate measure to halt the biodiversity loss.