PS 35-165 - Partitioning the impact of trait evolution on variability in range expansions

Background/Question/Methods

Range expansions are eco-evolutionary processes with important ramifications for current global changes, especially relating to invasive species and range shifts due to climate change. Recent work has highlighted the important role that trait evolution can play in increasing both the speed and variability of expansion outcomes. However, multiple traits are known to evolve in range expansions and the relative contribution of each to variability in expansion rates is unknown. Here, we use a genetically-explicit, individual-based simulation model to understand how evolution in dispersal, fecundity, or both can influence variability in range expansions. Specifically, we compared four models: (1) a model with no trait evolution, (2) a model with evolution in dispersal but not fecundity, (3) a model with evolution in fecundity but not dispersal, and (4) a model with evolution in both fecundity and dispersal. We parameterized our models with data from experimental range expansions using the red flour beetle (Tribolium castaneum). For both the experimental range expansions and simulation models, we used linear landscapes of discrete patches and assessed the speed and variability of expansion over eight generations.

Results/Conclusions

Experimental range expansions showed a dramatic increase in the variability of distance spread due to evolution, as well as evolved increases in dispersal and decreases in fecundity at the edge of expansion. When comparing the variance in distance spread between a model with no trait evolution (baseline) and a model with dispersal evolution, we saw an even greater effect of evolution than seen in our experimental landscapes. The experimental landscapes showed a 53% reduction in variance without trait evolution, but the baseline model showed a 93.5% decrease in variance compared to the dispersal evolution model. This discrepancy suggests that models considering dispersal evolution alone might be insufficient to understand and predict the dynamics of range expansions. We are in the process of building and analyzing the other models mentioned above (fecundity evolution and fecundity with dispersal evolution) to better understand how evolution of multiple traits affects variability in the outcomes of range expansions. Our aim is to use these models for predicting the dynamics of range expansion and to partition the impacts of evolution in different traits on variability in expansion outcomes.