DISSERTATION RESEARCH: Do trait correlations and demographic stochasticity alter the dynamics of evolutionarily-accelerated invasions?

William Marsh Rice University, Houston TX

Investigators

Abstract

The speed at which species spread across a landscape is often under-predicted because researchers do not acknowledge that dispersal and reproductive rates can respond due to natural selection. When the expansion of a harmful invasive species or a rare re-introduced species is under-predicted, societal implications can be significant. This project will correct chronic under-prediction of species' spread by measuring genetic correlations between dispersal and fecundity. Accounting for the effects of natural selection on range expansion will significantly improve management of invasive species by providing accurate estimates of their spread. The project will improve the research and training of a promising young investigator. Two undergraduate students will be trained in experimental, computational, and mathematical ecology. The researchers will develop lessons for Texas middle-school students from minority and economically-disadvantaged backgrounds to teach the causes and consequences of biological invasions, highlighting the importance of rapid evolution. During range expansion, individuals become spatially sorted by dispersal ability. Populations at the leading edge are dominated by highly dispersive individuals that mate assortatively. Spatial sorting will increase dispersal in leading edge populations over generations when dispersal is heritable, resulting in evolutionarily-accelerated invasions. Edge populations also occur at low conspecific densities, gaining a reproductive advantage. The theory of spatial selection is based almost entirely on models. This project examines the importance of spatial selection in ecologically realistic contexts, using laboratory-based experiments and computer simulation models to understand when spatial selection is likely to play an important role in range expansion, and when, or if, it is likely to have negligible effects. It will examine how genetic correlations between dispersal and fecundity modify expectations for spatial selection, using simulation models parameterized with data from a common beetle. The researchers hypothesize that negative genetic correlations between dispersal and fecundity will mitigate the effects of spatial selection, while a positive genetic correlation will amplify the effects. The second study will examine how stochasticity interacts with spatial selection to affect invasion speed. Demographic stochasticity may slow invasions by reducing the number of individuals at the leading edge of the invasion or by weakening the signal of spatial sorting and reducing reproductive potential at the invasion edge. This signal should be further reduced as dispersal heritability decreases. The researchers will integrate these two studies to elucidate conditions under which spatial selection is more or less important as a driver of invasion dynamics.