Meeting Abstract
Recent interest in the application of phylogenetic analyses to community data has allowed the ability to tease apart the relative contribution of ecological and evolutionary processes in structuring local species richness. In addition, comparing communities along an elevational gradient provides the opportunity to test hypotheses regarding the control of local species richness, because of the change in abiotic factors and turnover of species in a restricted geographic region. I quantified passerine bird species diversity along an elevational gradient in the Sky Islands of southeastern Arizona. I censused birds along a series of transects located in 5 different habitats types: Sonoran Desert, Oak Woodland, Oak-Pine Woodland, Pine Forest, and Fir Forest. I first estimated conventional patterns of species richness and species turnover. I next estimated the patterns of phylogenetic structure and diversity among the communities. I also quantified phylogenetic beta diversity to examine turnover in richness. The advantage of phylobetadiversity is that it measures the phylogenetic distance among communities as species composition changes. Moreover, the index links local processes, e.g., biotic interactions, with regional processes, e.g., speciation rates. Bird species richness and phylogenetic diversity exhibited a unimodal distribution with a peak at mid-elevations. Passerine bird communities exhibited phylogenetic overdispersion at the low elevation habitat and phylogenetic clumping at high elevation habitats. Compositional similarity declined with elevation. The phylogenetic distance-decay curve also declined with elevation and differed from significantly from the null expection, which suggests strong spatial structure along the gradient. These patterns suggest that biotic interactions structure communities at low elevations whereas environmental filtering characterizes the structure of high elevation communities.
