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).