The relative influence of habitat density, landscape configuration and spatial sorting on population expansion: a simulation test

Abstract Context Population expansion into new areas is a common phenomenon resulting from changes in ecological conditions or human-assisted introduction. In the latter case, populations spread into areas where they did not evolve causing various ecological and socio-economic impacts. Spatial sorting ( i.e. the enhanced dispersal capacity over time at the periphery of an expanding range) and landscape are two major factors affecting spread dynamics in expanding populations. Objectives While both factors have been frequently studied independently, their relative influence to modulate the spread rate of expanding populations has been significantly unexplored. We addressed this issue through a modeling approach. Methods We simulated the spread of an invasive amphibian, Xenopus laevis , in various landscape windows within and around its colonized ranges in western France. Using UNICOR, we ran colonization simulations on 30 km × 30 km windows of an experimentally parameterized resistance layer at three intensities of spatial sorting. Results Habitat (pond) density and spatial sorting positively affected the rate of population expansion in the windows and interacted: higher spatial sorting and pond density increased the invaded area, number of colonized ponds, and maximal traveled distance per time unit. In contrast, none of the four landscape configuration metrics improved the models, suggesting that they have limited influence on population expansion. Thus, the effect of spatial sorting on population spread was enhanced by pond density but not by landscape configuration. Conclusions Our results highlight the importance to jointly consider habitat density and spatial sorting in predictive modeling of the spread process in expanding populations, particularly for biological invaders.