CORBIN, C.E.*; MILES, D.B.; ERNST, N.; Bloomsburg University of Pennsylvania; Ohio University, Athens; Bloomsburg University of Pennsylvania: Age of evolutionary origin or ecological diversity: which better explains the morphological disparity of New World flycatcher clades?

Evolution of sister groups within a monophyletic clade is due to a combination of common and unique evolutionary processes. In some cases, the morphological evolution is linearly related to time since origin. In others, evolution is less Brownian. One reason for the latter is that there is greater ecological diversity in one sister group compared to another. We used a published phylogeny, published and observed foraging behavior, and morphological measurements on a synoptic series of species in the empidonax group of tyrant flycatchers (Aves) to test the following: Morphological evolution increases in ecologically diverse groups faster than 1) a Brownian motion model of evolutionary change and 2) non-ecologically diverse sister groups. Also, these clades were compared to two other species rich clades of flycatchers: the generalist elaenia and specialist tody-tyrants. We used multivariate and resampling techniques to characterize the morphological space and disparity of the clades. First, we used regression analysis to test for a linear relationship between time since origin and morphological variability. Bartlett statistics were used to test for differences in variance among sister groups. Results indicate that ecologically diverse and older groups had higher morphological variability but the relationship was not linear. Certain young, ecologically diverse groups had higher than expected morphological variability. Hence, during the morphological evolution of a species rich radiation of birds, Brownian evolution is often times overshadowed by ecological opportunity.