The importance of phylogeny in dictating the strength of competition

Background/Question/Methods

Competition is a key process in ecology that helps to determine the structure of communities.  Traditionally interspecific competition has been considered to be greatest in strength between closely related species, as reflected by much of the literature.  However, when interactions between distantly related species have been examined, competition has frequently been found to be important.  To test for generalities in the relationship between strength of competition and the relatedness of study species, we conducted a meta-analysis of published studies on competition.

To collect our data, we conducted a search using Web of Knowledge between the years 1992 and 2008 of eight high-impact ecology journals (American Naturalist, Ecological Monographs, Ecology, Journal of Animal Ecology, Journal of Ecology, Journal of Experimental Marine Biology and Ecology, Oecologia, and Oikos) using the terms ‘interspecific competition’.  Before further examination, all papers were required to meet a set of six criteria: that the study was conducted at an appropriate scale for the species used, pairwise comparisons were possible between species, densities of at least one species were manipulated, appropriate controls were used, that the effect measured was of a certain type (e.g. biomass), and that means, variance, and sample size were reported.  Phylogenetic distance between study species was then estimated using the TimeTree database and other published phylogenies.

Results/Conclusions

We found that the majority of studies were conducted on interactions between relatively closely related taxa.  This was particularly true for animals, and in terrestrial habitats.  Conversely, there were many more studies examining interspecific competition between distantly related plant species.  Phylogenetic distance was not necessarily a strong predictor of the strength of interspecific competition, as we found species from different phyla could compete with each other as strongly as species from the same family.  Our findings further emphasize the need to consider that species can have strong direct interactions with other distantly related and morphologically distinct species.