PARENT SESSION
Contributed Oral Session 45: Evolutionary / Theoretical Ecology : Genotypes and Phenotypes
Tuesday, August 9, 8:00 AM - 11:30 AM, Meeting Room 519 A, Level 5, Palais des congrès de Montréal
Competitive intensity is independent of phylogenetic relatedness among vascular plants.
Cahill, James*,1, Lamb, Eric1, Kembel, Steven1, Keddy, Paul2, 1 University of Alberta, Edmonton, Alberta, Canada2 Southeastern Louisiana University, Hammond, LA
ABSTRACT- A central goal of community ecologists over the last several decades has been to reconcile the "competitive exclusion principle" with the reality that species actually do coexist in natural systems. A central axiom of competition theory is that species will compete more strongly with closely related species than they will with more distantly related species, since closely related species will be more similar in terms of niche structure and will exploit resources more similarly than less closely related species. This idea is pervasive in community ecology, and is central to many aspects of major models and theories such as niche theory, niche differentiation, limiting similarity, and character displacement. Although there have been a variety of tests of this hypothesis using relatively small number of species (e.g. comparing competition among congeners vs. more distantly related species), a large comparative test of this central concept is lacking. We tested the question of whether the strength of competition was related to phylogenetic distance among competitors using several published data sets that measured the strength of competition among large numbers of vascular plant species. Each study used a phytometer approach, in which competition was measured as the suppressive effect of a given species on a common competitor species (competitive effect). For each data set we constructed a current phylogeny using Phylomatic, based upon APG II phylogenies, and then estimated the phylogenetic distance between the competing species both as nodal counts and measures of estimated branch lengths. We then tested for correlations between phylogenetic distance and competitive intensity. In all data sets, the strength of competition was independent of phylogenetic distance between the competing species. These findings raise significant questions about the validity of a central tenet in community ecology and competition theory. Although this finding is surprising in that it is counter to standard ecological dogma, it is not particularly surprising given a basic understanding of the mechanisms of plant competition. It remains to be seen whether this finding can be generalized to other taxa, or if it is specific to plants which have strongly overlapping "diets".
Key words: competition, niche, phylogeny, plant