Differential establishment and survival mediated by the abiotic environment (environmental filtering) and differential arrival due to dispersal limitation are two key processes hypothesized to maintain diversity in plant communities. Environmental filtering can promote coexistence via stabilizing niche differences, while dispersal limitation can slow competitive exclusion and maintain diversity at the landscape scale by increasing intraspecific aggregation. Unfortunately, these processes have often been studied separately within distinct theoretical frameworks. Progress in the study of community assembly therefore requires frameworks of analysis that allow for the simultaneous consideration of both processes. Here, we use spatial point pattern modeling to infer the relative importance of both environmental filtering and dispersal limitation as drivers of community structure and diversity in a hyperdiverse Amazonian forest in Ecuador. In addition, we tested if a suite of field-collected physiological and functional traits are correlated with metrics related to each process.
We find that on average across the 457 most abundant tree species in the plot, representing over 90% of the stems, dispersal limitation inferred from the spatial models explains 56% of spatial variation in species distributions, while responses to topography and soil nutrients explain 44%. In addition, despite the forest being largely aseasonal, environmental filtering at this site appears to be driven in part by drought tolerance, as measured via leaf osmotic potential. Finally, we found that seed mass was inversely correlated with intraspecific aggregation detected in the model. This suggests that dispersal limitation, often assumed to be neutral with respect to species identity, may be determined in part by species-specific differences in dispersal ability. Taken together, these results suggest that environmental filtering and dispersal limitation, meditated by the functional traits of species, act in concert to drive the spatial structure of diverse plant communities.