%0 Journal Article
%T Analyzing snapshot diversity patterns with the Neutral Theory can show functional groups¡¯ effects on community assembly
%A Adrien Taudi¨¨re
%A Cyrille Violle
%A Fabien Laroche
%A Fran£¿ois Munoz
%J Ecology - Wiley Online Library
%D 2019
%R https://doi.org/10.1002/ecy.2977
%X A central question of community ecology is to understand how the interplay between processes of the Neutral Theory (e.g., immigration and ecological drift) and niche©\based processes (e.g., environmental filtering, intra©\ and interspecific density dependence) shape species diversity in competitive communities. The articulation between these two categories of mechanisms can be studied through the lens of the intermediate organizational level of ¡°functional groups¡± (FGs), defined as clusters of species with similar traits. Indeed, FGs stress ecological differences among species and are thus likely to unravel non©\neutral interactions within communities. Here we presented a novel approach to explore how FGs affect species coexistence by comparing species and functional diversity patterns. Our framework considers the Neutral Theory as a mechanistic null hypothesis. It assesses how much the functional diversity deviates from species diversity in communities, and compares this deviation, called the ¡°average functional deviation,¡± to a neutral baseline. We showed that the average functional deviation can indicate reduced negative density dependence or environmental filtering among FGs. We validated our framework using simulations illustrating the two situations. We further analyzed tropical tree communities in Western Ghats, India. Our analysis of the average functional deviation revealed environmental filtering between deciduous and evergreen FGs along a broad rainfall gradient. By contrast, we did not find clear evidence for reduced density dependence among FGs. We predict that applying our approach to new case studies where environmental gradients are milder and FGs are more clearly associated to resource partitioning should reveal the missing pattern of reduced density dependence among FGs. A central goal of community ecology is to understand the processes that underpin species diversity in space and time. Several theories have been proposed to explain how species coexist within a single trophic level. The Niche Theory has focused on how differences in per capita growth rate among species can or may not allow coexistence (Grinnell 1917, Hutchinson 1957). These differences can come from two ¡°niche©\based¡± processes: density dependence and environmental filtering. Density dependence refers to the fact that the per capita growth rate of some focal species depends on its own density (intraspecific density dependence) and on the density of other species in the community (interspecific density dependence). In competitive communities, these relationships are thought
%U https://esajournals.onlinelibrary.wiley.com/doi/full/10.1002/ecy.2977