Island plant communities: Geographic isolation and community function

Background/Question/Methods

Plant functional traits are an important driver of ecosystem processes and are increasingly used to quantify variation in community functioning. Although many studies have examined how plant functional traits vary across environmental gradients, few have tested how community functioning changes with spatial isolation. Other studies found that island isolation gradients can explain the varying subsets of species based on specific dispersal strategies, but did not explicitly test how these subsets of species may also provide a unique composition of functional traits. In this study, we used species composition data from 36 Maine coast islands to quantify functional traits and seed dispersal strategies across a gradient of isolation. 

Results/Conclusions

Our results show that islands harbor a progressively disproportionate composition of growth forms and seed dispersal strategies with increasing isolation. For example, tree and shrub species richness significantly declined relative to forbs and graminoids. Contrary to previous studies, we also found that bird-dispersed species richness declined most rapidly across isolation. These results provide compelling evidence towards the importance of combining plant functional trait ecology with island biogeography. Our findings may also provide key insights about the ecosystem functioning of fragmented landscapes. Further studies examining the functional composition of islands will be crucial for the conservation of insular habitats—especially in light of climate change.