Large-scale biodiversity gradients are one of ecology’s most fundamental patterns; yet, for many of these diversity patterns, the existence and identity of a unified cause remains controversial. At the community level, biodiversity is presumably maintained by two major forces-- the abiotic environment, and the biotic interactions between species present within communities. Because both of these forces act more directly on communities’ functional identity than they do on taxonomic or phylogenetic composition, recent literature has focused on functional trait approaches in identifying the presence and relative importance of biotic and abiotic forces in the assembly of varying communities.
Here, we characterize patterns of alpha and beta functional diversity that are present in multitrait functional hypervolumes for woody plant communities in six elevational forest gradients, spanning a 30-degree latitudinal gradient across North and Central America. We use these patterns of functional diversity to investigate drivers of community assembly along these elevational gradients, and whether or not similar drivers seem to be acting on elevational communities across a latitudinal span.
Results/Conclusions
We find consistent patterns of functional diversity in relation to species richness and elevational shift across the six forest gradients, despite the large shifts in latitude and climate that separate these sites. However, these patterns do not appear to be consistent with any one theory of biodiversity and community assembly. Species rich sites (more than 30 species) are found to be functionally dispersed, possibly reflecting a biotic competition and niche-diversification dynamic. However, functional similarity of sites within gradients appears to decrease with increasing elevational separation, and certain traits appear to undergo directional shifts, which is more consistent with abiotic filtering. These apparently contradictory results may suggest that both biotic and abiotic forces are important in the assembly of woody plant communities; however, the consistency of our results across latitudinally disparate gradients also suggests that the balance of these forces is minimally affected by changes in the individual climate at these forests.