Abstract
Dispersal is apt to evolve upwards on invasion fronts due to assortative mating by dispersal, a phenomenon known as the “Olympic Village effect” or spatial sorting. But what happens after the invasion front has passed? Empirical and theoretical studies have suggested a decline in dispersal following invasion, but hypotheses about what drives this decline have not been clearly articulated or tested. Here we use a simple model of the spatiotemporal dynamics of two dispersal phenotypes to propose a general explanation. Following invasion, spatial sorting drives dispersal of its inhabitants downwards. This shift is fleeting, however, as a mixture of fast and slow phenotypes sets in as equilibrium densities are attained. Afterwards, dispersal only continues to evolve downwards if there is a trade-off between dispersal and fitness at high density. We conclude that empirical observations of declines in dispersal following invasion imply the existence of a trade-off between dispersal and fitness.