Meeting Abstract
Migration theory posits that inter-specific competition drives the evolution of migration. However, this view omits the role of genetic drift, natural selection, and intra-specific competition in shaping niches. We addressed this discrepancy by combining theories of niche divergence and the evolution of migration in birds to examine the evolution of niches in migratory, partially migratory and resident populations in the Tyrannus genus of birds. We found support for the hypothesis that migrants demonstrate evidence of resource polymorphism since they are more generalist foragers than residents along a gradient of increasing variation in morphology from fully resident to fully migratory populations. We found convergence of the morphologies of traits important for niche differentiation for migratory (generalist) versus resident (specialist) life history strategies. Our results demonstrate that differences in morphology between migrants and residents should not be taken conclusively as evidence of niche partitioning due to inter-specific competition. Instead, we suggest that intra-specific competition may promote resource polymorphism as one aspect of the suite of co-adaptations that are adaptive for migratory populations, compared to specialist resident populations. More research is needed contrasting inter- and intra-specific competition to improve our understanding of how these processes shape the evolution of divergent life-history strategies.
