Predicted and observed short-term trait evolution
Over the first 25 cycles of the evolutionary experiment, we observed a strong increase in dispersal in the range front treatment (Fig. 1B). Dispersal reached 22.3% (± 0.012 SE, averaged over cycles 15-25) at the front, compared to only 4.4% (± 0.004 SE) in the core treatment and 6 % (± 0.012 SE) in the control treatment (effect of selection treatment: χ22 = 119.7; p < 0.001). Increased dispersal at the front established within only a few cycles, and was formally significant for the first time at cycle 8 (cycle-by-cycle analysis: p < 0.001). Our parametrized model captured this rapid increase of dispersal in the range front treatment (Fig. 1B), and there was a quantitative match between the distribution of endpoint levels of dispersal in the model and observed values in the experiments (Fig. 2A). The model further predicted general increases in growth rate (r0) and equilibrium density (\(\overline{N}\)) in all treatments, from 0.07 in the ancestral mix to 0.08 in core and front end-point populations. This is consistent with results from the growth assay conducted at cycle 21, where estimates of r0 for the 15 lines are well within the central range of predicted values in the model (Fig. 2B). As predicted, the evolutionary treatments did not significantly differ in r0(treatment: F2,12 = 1.2; p = 0.354). Unlike in the model, range front lines produced nearly 20% higher equilibrium densities than did range core and control lines (treatment: F2,12 = 11.1; p = 0.003).