Strategy differentiation and coexistence in an Amazonian forest

Background/Question/Methods The astounding diversity of moist tropical forests has proved to be an enduring challenge to ecologists, and has inspired many important theories of species coexistence and contentious debate. A central question is whether functional strategies, or niche differentiation, which plays a key role in much of classic ecological theory, is important or even plausible in highly diverse communities. However, many large-scale analyses of tropical forest tree assemblages have treated species as functionally equivalent units. Growing consensus among plant ecologists now permits the quantification of plant strategies along a number of important ecophysiological axes, opening the door for previously intractable analyses. To test the prediction that tropical trees are distributed at random with respect to functional strategy, we applied recently developed methods in functional trait-based community ecology to one of the most diverse tree communities ever censused- the 1,100+ species, 25-hectare Yasuní plot in Amazonian Ecuador. We combined census data on the spatial location of over 150,000 trees with field-collected measurements of key functional traits in order to characterize the ecological similarity of co-occurring species at small (0.04 ha) spatial scales. Results/Conclusions Using a null model approach, we have demonstrated that trees in Yasuní are distributed in a decidedly non-random fashion with respect to strategy, which is evidence against a purely neutral explanation of species coexistence. Furthermore, we find evidence for processes that simultaneously drive convergence and divergence in key aspects of plant strategy, suggesting that at least two distinct niche-based processes are occurring. Our results demonstrate that strategy differentiation among species shapes one of the most diverse tropical forests in the world.