At small spatial scales competition and limited dispersal can obscure and reduce the effects of environmental variation on community composition, while the strength of environmental control tends to increase at larger spatial scales. Despite this, other factors can influence assemblage structure at the macro scale such as regional variation in speciation rate and available area, both of which affect the sizes of regional species pools, or gamma diversity. Many classical metrics of community turnover, or beta diversity, are not independent of gamma diversity and data is often limited, which makes comparing levels of turnover between regions difficult. Here we use taxonomic and phylogenetic metrics of beta diversity that are largely invariant to gamma diversity to map plant beta diversity across the Americas using a dataset with broad geographic and taxonomic coverage. We then ask which aspects of climate and topography are most strongly associated with community turnover while controlling for autocorrelation in environmental variation.
Results/Conclusions
We found that beta diversity is on average higher in the tropics for metrics emphasizing recent divergence, but that there is significant variation between both regions and metrics. For example, levels are moderate-low in the Amazon basin and high in some temperate areas, especially mountains. Areas with higher mean annual temperature and less seasonal variation in temperature have higher beta diversity, while larger local elevational range also increased beta diversity. Taken together, these results highlight the importance of seasonal and elevational variation in temperature as a major driver of plant community composition across the Americas, which has important implications as temperatures are altered due to climate change.