Abstract: 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. I extracted the mean, standard deviation, and sample size of 355 core and edge traits from 44 studies across 27 Species. Using Bayesian random slopes meta-analyses, I partitioned variation in core-edge differences into components for species, among-study variation, within-study variation, and trait function (dispersal, reproduction, body size, growth rate, energy, defense, and environmental tolerance). A similar model was used to test for changes in variation. I assessed publication bias by adding adding terms for reciprocal sample size to the mean-shift model and using K-fold cross validation and posterior predictive stacking to compare it to model without those terms. While most variation was explained by within-study effect (corresponding to high heterogeneity among traits), populations showed traits showed a significant increase in dispersal-related traits. There were marginal increase in r-selected reproductive strategies and environmental tolerances, both coupled with a marginal reduction in phenotypic variance. Other trait groups show no consistent core-edge changes in mean or variance, and publication bias was not a significant contributor to the results. Broadly, these findings are qualitatively concordant with the theoretical expectations: range expansions are heavily influenced by stochastic events, but dispersal evolution is a common if not universal occurrence.
