PATTERNS AND CORRELATES OF ECOMORPHOLOGICAL DIVERSIFICATION IN BIRDS

A fundamental theme in macroevolution is understanding the origin and drivers behind the accumulation of phenotypic diversity in deep-time. Specifically, we want to describe and explain the mode (how) and tempo (at what speed) of morphological differentiation between species. Here, I investigate the patterns and correlates of ecomorphological diversification across the most diverse radiation among the tetrapods - birds. First, I investigated how variation in evolutionary rates impacts inferences from models of trait evolution. I show that rate-static models can produce spurious interpretations regarding the process of trait evolution in the presence of rate-heterogeneity, whereas robust conclusions can be drawn by co-utilizing rate-variable approaches and tests for absolute model adequacy. Second, I use a multipredictor approach to investigate correlates for the tempo of beak shape evolution across more than a half of bird species. I find high rates of evolution in morphologically-distinct clades as well as in species-rich groups, showing that ecological opportunity and species-packing impact the tempo of ecomorphological diversification in deep-time. Thirdly, I apply trait evolutionary models with competition alongside ecologically-neutral models to investigate the mode of beak shape, beak size and body mass evolution across birds. I show that models with species-interactions are not uncommonly the best fit for the data in clades, and thus ecological selection pressures can impact the accumulation of morphological diversity at deep-time scales. Lastly, I investigated how competition affects the process of ecomorphological evolution in sympatric avian granivorous assemblages. I find that species-interactions contribute to increased morphological diversity across the globe, however, the strength of competition signal is mediated by the negative association with the tempo of trait evolution. Taken together, these results explore how key ecological processes (the presence and absence of ecological opportunity, niche packing, the strength and resolution of competition) can explain variation in how biodiversity accumulates in deep time.