Evolutionary theory holds that ecological diversification in species radiations result in specialists evolving by partitioning niches or resources, although phylogenetic analyses have failed to produce conclusive results whether this trend exists. However, such hypotheses have not often been used to explain patterns in species range size and distributions from a phylogenetic approach. Using phylogenetic community ecology methods to test hypotheses about patterns of shared ancestry on species coexistence, we investigate whether species radiations lead to niche separation in angiosperm vegetation communities of the Rocky Mountain National Park, Colorado. Specifically, we test whether species occupying large range distributions along an elevation gradient are more closely related (phylogenetically clustered; PC ) or distantly related (phylogenetically overdispersed; PO) to each other than random. We are additionally interested to see how species ranges and phylogenetic relatedness change over an environmental gradient of increased elevation.
One of two patterns is hypothesized: (1) PC species possess shorter range distributions than PO species; or, (2) PC species occupy larger range distributions than PO species. Under the first hypothesized scenario, overdispersion is expected for species occupying large niche space (generalists), and clustering for species occupying small niche space (specialists); species become more distantly related as elevation increases. In the latter, PC of species would indicate that shared physiological tolerances along the environmental gradient are the primary structuring mechanism; species become more closely related as elevation increases.
Results/Conclusions
For our preliminary data analysis, we constructed a phylogenetic supertree (angiosperms; Davies et al., 2004) used to derive phylogenetic distance matrices. While no obvious trend was observed between phylogenetic relatedness and elevation (r = -0.01707) phylogenetic distance between species was observed to be unusually higher than expected (mean mean-pairwise distance=233.50,sd=21.959). Species’ range and distribution also appear to follow the mid-domain hypothesis, with intermediate-ranged species occurring at either high or low elevations. When basing niche separation on distribution range, the ratio of specialists to generalists is observed to be highest at low and high elevations. While multivariate analysis of species phylogenetic relatedness in relation to niche separation has not yet been conducted, we find that species are PO in their elevation range. In this poster, I present my preliminary data analysis.