Sex-biased dispersal and the speed of two-sex invasions

Author Posting. © University of Chicago, 2011. This article is posted here by permission of University of Chicago for personal use, not for redistribution. The definitive version was published in American Naturalist 177 (2011): 549-561, doi:10.1086/659628.Population models that combine demography and dispersal are important tools for forecasting the spatial spread of biological invasions. Current models describe the dynamics of only one sex (typically females). Such models cannot account for the sex-related biases in dispersal and mating behavior that are typical of many animal species. In this article, we construct a two-sex integrodifference equation model that overcomes these limitations. We derive an explicit formula for the invasion speed from the model and use it to show that sex-biased dispersal may significantly increase or decrease the invasion speed by skewing the operational sex ratio at the invasion’s low-density leading edge. Which of these possible outcomes occurs depends sensitively on complex interactions among the direction of dispersal bias, the magnitude of bias, and the relative contributions of females and males to local population growth.This work was supported in part by a Woods Hole Oceanographic Institution Summer Student Fellowship and a National Science Foundation (NSF) Graduate Research Fellowship to A.K.S., USDA grants to T.E.X.M. (CSREES-2007–02270), and NSF grants to M.G.N. (DEB-0235692) and to B.D.I. (DEB-0816838). T.E.X.M. was also supported by the Rice University Huxley Fellowship; M.G.N. also acknowledges support fromthe AndrewW. Mellon Foundation Endowed Fund for Innovative Research