Opposing assembly mechanisms in a Neotropical dry forest: implications for phylogenetic and functional community ecology

Abstract

Abstract. Species diversity is promoted and maintained by ecological and evolutionary processes operating on species attributes through space and time. The degree to which variability in species function regulates distribution and promotes coexistence of species has been debated. Previous work has attempted to quantify the relative importance of species function by using phylogenetic relatedness as a proxy for functional similarity. The key assumption of this approach is that function is phylogenetically conserved. If this assumption is supported, then the phylogenetic dispersion in a community should mirror the functional dispersion. Here we quantify functional trait dispersion along several key axes of tree lifehistory variation and on multiple spatial scales in a Neotropical dry-forest community. We next compare these results to previously reported patterns of phylogenetic dispersion in this same forest. We find that, at small spatial scales, coexisting species are typically more functionally clustered than expected, but traits related to adult and regeneration niches are overdispersed. This outcome was repeated when the analyses were stratified by size class. Some of the trait dispersion results stand in contrast to the previously reported phylogenetic dispersion results. In order to address this inconsistency we examined the strength of phylogenetic signal in traits at different depths in the phylogeny. We argue that: (1) while phylogenetic relatedness may be a good general multivariate proxy for ecological similarity, it may have a reduced capacity to depict the functional mechanisms behind species coexistence when coexisting species simultaneously converge and diverge in function; and (2) the previously used metric of phylogenetic signal provided erroneous inferences about trait dispersion when married with patterns of phylogenetic dispersion.

Interspecific Functional Convergence and Divergence and Intraspecific Negative Density Dependence Underlie the Seed-to-Seedling Transition in Tropical Trees

“…When we considered the functional evenness and mean nearest neighbor distance of individual traits, we found that not all traits are behaving similarly, as has been noted in previous tropical tree research comparing multivariate and individual trait dispersion patterns (e.g., Kraft et al 2008;Swenson and Enquist 2009). Specifically, wood density and leaf area showed higher functional evenness and mean nearest neighbor distance than expected, indicating a thinning of individuals with similar wood density and leaf area values.…”

“…We used the positions of species along the first two PCA axes, which together explained 51% of the total variation for the multivariate analyses. Previous research on static adult tropical tree assemblage data sets has shown that the degree of local trait diversity varies by trait, reflecting divergence and convergence operating simultaneously on the functional similarity (e.g., Swenson and Enquist 2009). Thus, we performed the univariate and multivariate analyses described below.…”

“…Seedling and sapling studies have argued for the importance of negative density dependence (Harms et al 2000;Metz et al 2010), abiotic filtering , or stochastic survivorship (Paine and Harms 2009). However, it is more likely that all of these factors act at the same time (e.g., Swenson and Enquist 2009), making it important to disentangle their importance in structuring tropical tree communities through space and time.…”

Phylogenetic conservatism of functional traits in microorganisms

“…Prinzing and co-workers find that among plants in Europe, tolerance of extremes in soil moisture was associated with higher taxonomic levels than were those for temperature or light (Prinzing et al, 2001). Similarly, tree height and seed mass are linked to broader phylogenetic groups in comparison with other functional traits in trees (Swenson and Enquist, 2009).…”

“…Furthermore, it can identify the actually sequence divergence defining ecologically coherent units (at least in respect to one trait) rather than the taxonomic level associated with a trait. The latter has been done in some recent studies of plants due to the lack of a detailed phylogenetic tree (Prinzing et al, 2001;Swenson and Enquist, 2009). For microorganisms, however, there is an abundance of sequence data and organisms are mostly classified based on phylogeny and this can be used directly for the consenTRAIT analysis.…”