Mitigating the spread of invasive species requires an understanding of both the ecological and evolutionary factors which drive their range expansion. Evolutionary changes during invasions/range expansion, for example, may alter the dispersal and reproductive traits of invading populations - affecting their ability to spread to- and reproduce in new territory. Previous studies have indicated that selective pressures at the invasion front yield individuals that disperse further and faster. It is still unclear, however, how the impact of spatial evolution varies between species and across different landscapes. In this study, two species of flour beetles (genus Tribolium) were each reared in two different environments, then allowed to disperse over a ‘landscape’ of interconnected patches. Two environmental treatments were applied to both species of beetle- a wet/high-quality environment, and a dry/stressful environment. After 5 generations of dispersal, individuals from the farthest extent of the species range (the edge, or invasion front) were compared to those at the densely-populated center (the core) of the species range. Core and edge individuals were placed in a common garden for 1 generation, after which we measured their dispersal ability and reproductive potential.
After 5 generations of experimental range expansion, Tribolium castaneum beetles dispersed across up to 16 patches in the dry environment, and 14 in the wet; Tribolium confusum dispersed across as many as 6 patches in the dry environment, and 7 in the wet. The dispersal of T. castaneum in the stressful dry environment was on average higher and more variable than in the wet environment. This may indicate that individuals in less-desirable habitats have a greater incentive to disperse further in search of suitable habitat. Results from the common garden experiment indicate that the T. castaneum beetles from the edge populations disperse further and have lower reproductive rates than those from the core. No significant difference between core and edge populations was found for T. confusum- likely due to their minimal dispersal. These results support the idea that spatial evolution is important in the spread of invasive species and that its impacts depend partly on species-identity and environmental-context.