Print PageMany models of population growth and spread predict that the population density of an invading species takes the form of an invasion wave spreading with constant speed. Almost without exception, these models track the population density of only one sex (typically females). Nevertheless, males and females of a given species frequently exhibit strikingly different dispersal distributions. The question is, how do these dispersal differences affect invasion speed?
To address this question we formulated a two-sex integrodifference equation model that incorporates the sex-related biases in dispersal and mating behavior that are typical of many animal species. From this model we were able to derive a formula for the invasion speed.
Results/Conclusions
Using our model and invasion speed formula, we will show that differences in the dispersal distributions of males and females can produce skewed sex ratios along an invasion front. This skew can dramatically effect predictions of invasion speed relative to the predictions from a one-sex model. The two-sex invasion speed may be larger or smaller than the one-sex speed. 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.
