Resource buffering and the evolution of bird migration
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- Bell, C.P. Evol Ecol (2011) 25: 91. doi:10.1007/s10682-010-9383-4
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Variation in migratory behaviour among birds is thought to reflect the relative variability in abundance of resources used by different species. Here I present evidence that increased migrancy among North American passerines is associated with greater reliance on food resources that vary in abundance because they occur in microhabitats that are exposed both to consumers and environmental fluctuation, and that residency is associated with use of food resources that occur in more ‘buffered’ microhabitats, and so are relatively invariant in abundance. Evidence from a variety of sources suggests that migrants and residents also differ in their use of foraging actions and methods of exploring the environment, with migrants using a rapid, extensive method of exploration, and a plastic, opportunistic foraging mode, while residents explore more methodically and use more stereotyped foraging actions. This suggests that the degree of migrancy exhibited by a species may be part of a suite of coadaptations for exploitation of foraging microhabitats at a particular position on the buffering scale, and I propose a selective typology involving feedback loops that could generate such coevolution. I also explain established patterns of difference between migrants and residents in morphology, and in resource use and distribution, as outcomes of the evolutionary scenario described.