Sex-Biased Dispersal and the Speed of Two-Sex Invasions

Abstract

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 sexrelated 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.

A comparative approach to testing hypotheses for the evolution of sex‐biased dispersal in bean beetles

“…2011), and a previous study showed that it provided a good fit to beetle recruitment data (Miller and Inouye 2011). Parameter λ represents the reproductive rate.…”

“…Patterns of movement differ among species and even among individuals of the same species, including age‐, stage‐, and sex‐specific movement (Neubert and Caswell 2000; Miller et al. 2011). A major goal of evolutionary ecology is to understand the selective forces that have shaped variation in dispersal behavior among and within species (Ronce 2007).…”

“…2011; Dobson 2013). The direction and magnitude of sex bias in dispersal varies across taxa and may be associated with taxonomic groups and / or mating systems.…”

“…Sex bias in dispersal can have important implications for the spread of invasive organisms (Miller et al. 2011; Miller and Inouye 2013) and for the genetic structure of metapopulations (Kerth et al. 2002; Fraser et al.…”

Dispersal Evolution in the Presence of Allee Effects Can Speed Up or Slow Down Invasions

“…This forces a model to ignore sex-specific differences not only in life-history traits, such as body size, survival, and age of maturation (Bradley et al 1980;Fairbairn 1997;Onyango et al 2013), but also in movement behaviors, such as tendency to leave the natal area and total distance traveled (Greenwood 1980;Waser and Jones 1983;Clarke et al 1997;Miller et al 2011). An added complication of sexually reproducing species is the requirement that individuals find mate(s) before reproducing, which can be increasingly difficult at low densities (Dennis 1989;Wells et al 1998;Courchamp et al 2008).…”