Trait shifts during range expansions: A meta-analysis

Populations undergoing range expansions often undergo phenotypic shifts at the leading edge. Understanding how traits change during range expansions could provide insight into predicting invasive species dynamics and responses to climate change. Theory predicts that edge populations should increase in dispersal capability and shift towards reproductive traits that maximize fecundity over individual offspring investment. I conducted a quantitative synthesis of previously published research across a variety of plant and animal taxa to test whether core-to-edge changes in trait means and variance follow these theoretical predictions. While most variation in core-edge shifts was explained by within-study effect (corresponding to high heterogeneity among traits), populations showed a significant increase in dispersal-related traits. There were marginal increases in r-selected reproductive strategies and environmental tolerances, both coupled with a marginal reduction in phenotypic variance. Other trait groups showed no consistent core-edge changes in mean or variance. These results show that trait shifts generally follow the expectations of range expansion theory and highlight the importance of considering changes in trait distributions instead of just mean shifts.