The influence of phylogeny in community ecology: Insights and challenges

Background/Question/Methods .  Phylogenetic history encapsulates many different properties of species.  At a broad scale, the distribution of a given species is heavily influenced by its geographic origin and subsequent movement across the landscape. The evolutionary contingencies and trade-offs that constrain ecological characteristics of species are encapsulated in their phylogenetic history, and, too, contribute to the habitats and areas species occupy.  Locally, interactions between species, and the ability of species to remain reproductively isolated, determine which species coexist.  All of these processes determine community composition at local scales. 

Experimental and descriptive approaches to community assembly offer different approaches to understanding the importance of evolutionary history. Descriptive approaches measure patterns of species co-occurrence and species’ trait values in communities, while experimental approaches use human-assembled communities to examine the importnace of interactions at local scales. Whether assembled or natural, studies that use local species, a practice that is typical, are constrained by the phylogenetic distances between species present at field sites.

Results/Conclusions .  Several caveats apply to both experimental and descriptive approaches. The underlying distribution of phylogenetic distances varies across  communities, but yet is rarely related across studies. This variation in phylogenetic distance may compromise the extension of results across communities, or may explain conflicting results across studies.  Phylogenetic dispersion metrics tell us about relatedness relative to a null community, but do not reflect the absolute distances among species. Thus, overdispersion in communities sampled from a pool of close relatives may reflect one process,  e.g., limiting similarity, while overdispersion in communities sampled from a pool of more distantly related species may reflect different underlying processes. Second, the processes that contribute to assembly of field communities may have already influenced the phylogenetic distances present among members  (“ghost of assembly past”). For example, an analysis of 67 sister pairs in the California flora showed that range overlap of sister species is low, despite similarity in ecological niche properties of climate, growth form, and flowering time (See Anacker and Strauss Symposium Thurs 1:30). Thus, extant communities are generally lacking species pairs with the shortest divergence times.  Whether this is due to reproductive isolating mechanisms, ecological interactions, or both, remains to be determined. Future work calibrating divergence times across communities, and using experimental assembly of communities with species that vary in phylogenetic distance, potentially including taxa that currently do not coexist, may contribute to further understanding of how evolutionary history influences community assembly.