The scaling of biodiversity between local and global scales, or beta diversity, can provide insight into the processes that generate and maintain biodiversity. Across time and community development, the contribution of different biodiversity drivers may shift. While previous work details the relative importance of environmental variation and dispersal limitation for plant communities across succession, our understanding of temporal changes in communities at higher trophic levels is underdeveloped. We use a space for time chronosequence to understand how communities change in their species composition with increasing geological substrate age. We examine whether communities converge or diverge in their species composition over long time scales, and at what spatial scale most species turnover takes place. Then, we explore whether insect communities assemble chronologically, and turnover happens in a predictable way such that similarly aged communities are also similar in species composition. We also examine the alternative where the community is structured by dispersal limitation, forest structure and host leaf traits. and whether communities in close proximity are more similar. We study this in an herbivorous insect community associated with the host plant Metrosideros polymorpha on Hawai‘i. We sampled M. polymorpha canopies and collected Hemiptera across Big Island, Maui, Moloka‘i and Kauai.
Results/Conclusions
Our results show that across the chronosequence, turnover in species composition decreases, indicating that communities converge over time. In examining drivers of turnover, we detect a strong signature of forest structure and leaf traits indicating the importance of local species sorting across habitats. In contrast, both dispersal limitation and substrate age did not correlate with dissimilarity in community composition. Furthermore, local beta diversity was highest in dynamic, early succession communities, and decreased across the chronosequence. Together, these results suggest that assembly processes for M. polymorpha herbivore communities vary over time, that the communities are primarily structured by habitat preference, and that dispersal limitation does not drive these Hemiptera communities. Surprisingly, similarity in age did not correlate with community similarity, raising the possibility that the species pool associated with M. polymorpha is not geographically restricted within the islands. We argue that analyzing turnover within and between communities of varying temporal stages can elucidate biodiversity drivers, and is particularly relevant for higher trophic levels whose structure is not well explored.