Models that estimate invasion speed are used in both theoretical and applied studies of spreading populations. The invasion speed produced by these models depends on the vital rates (e. g., survival and fecundity) and the dispersal characteristics of individuals. These rates, in turn, typically vary among individuals in ways that can often be attributed to differences in some demographic state of the individual such as age or developmental stage. For animals and dioecious plants, sex is another demographic state that affects vital and dispersal rates. Here, we construct a model (a system of integrodifference equations) wherein individuals are classified by both age and sex.
Results/Conclusions
We derive an implicit equation for an upper bound on the invasion speed and show that it generally matches simulated invasion speeds. We use our model to demonstrate that invasion speed can vary greatly with mating system, particularly when dispersal is also sex biased. We also show that sex-biased dispersal and mating system affect the degree to which invasion speeds calculated from unstructured models or models with only age or sex structure overestimate the invasion speed of sex-and-age-structured populations.