Interspecific competition has well-documented effects on evolution in simple systems over short timescales. However, the effects in more complex communities, and over the timescales of continental radiations, are less clear. In this dissertation, I addressed the relationships between coexistence, morphological evolution, and diversification at multiple spatial and temporal scales, using birds in the family Picidae, which includes woodpeckers and the related piculets and wrynecks. Morphology of these birds is correlated with diet and foraging mode, allowing similarity in morphological measurements to be used as a proxy for ecological similarity. Members of Picidae occur throughout the Americas, Africa, and Eurasia, and local diversity ranges from a single species to up to 13. I first generated a phylogenetic hypothesis of Picidae, and then tested predictions from community ecology and macroevolutionary theory at the community level and across the entire global radiation of Picidae. In Chapter 1, I inferred phylogenetic relationships among ~75% of extant species of Picidae, the most comprehensive molecular phylogeny of the family to date, using publicly available sequence data augmented by targeted collection of new data. While most results matched previous findings, a few species with new molecular data were placed in unexpected regions of the tree, and several genera as currently delineated appear to be paraphyletic. Relationships within most genera and previously described tribes were well resolved, but relationships among most major clades remained unclear. A number of tightly spaced branching events near the base of the family were not resolved with available data. In Chapter 2, I evaluated the roles of ecological assortment of species and in situ trait evolution in driving trait distributions in communities of North American woodpeckers. I used multiple null models and metrics of community trait distributions to test for deviations from randomness in six communities including a total of 10 species. I recovered a signal of divergent displacement across all populations and all communities, suggesting local evolution away from morphologically most similar species. However, trait distributions in most individual communities did not differ from random expectations. In average size and overall morphology, one community showed evidence of species sorting for dissimilar traits. In the size-scaled shape data, I found evidence of divergent and convergent local evolution in one community each. These results suggest that trait differences are related to both species sorting and local evolution, but that other processes or a lack of statistical power prevent detection of effects in many communities. In Chapter 3, I tested for relationships between coexistence and rates and modes of diversification and trait evolution across all Picidae. I used phylogenetic comparative methods to evaluate correlations among subclades of Picidae in relevant variables. I found strong and consistent positive correlations between geographic range overlap, rates of diversification, and rates of shape evolution—but not body size or overall morphological evolution. In addition, time-dependent models of morphological evolution and diversification fit better to subclades with greater range overlap. Taken together, these findings suggest that coexistence with similar species does affect evolution in Picidae. Shape evolution shows clear connections with coexistence in both the community-level and family-wide comparative analyses. The community analyses suggest that coexistence is the cause, rather than the consequence, of this trait evolution, as the trait changes are more spatially restricted and temporally recent than apparent coexistence among many of the species. Variation in diversification rates may be driven by other factors that covary with local diversity and evolution in body shape. Future work in this group should focus on solving the remaining puzzles in phylogenetic relationships, determining the contribution of body size and shape to competitive interactions, and understanding possible relationships of other variables with diversification, morphological evolution, and coexistence. One online supplementary file (OSF) accompanies this dissertation: a spreadsheet containing the GenBank accession numbers or other sources for the DNA sequence data used in Chapter 1.
University of Minnesota Ph.D. dissertation. October 2015. Major: Ecology, Evolution and Behavior. Advisors: Fredrick Barker, Kenneth Kozak. 1 computer file (PDF); x, 186 pages.
Coexistence, Ecomorphology, and Diversification in the Avian Family Picidae (Woodpeckers and Allies).
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