Figure 4.
The relationship between variance in fitness at the start of a generation and the resulting genetic load, for two mean migration rates (A, B). Genetic load is defined as the reduction in mean fitness below its maximum of one, measured here in the first generation starting with no local adaptation (p0 = 0.5). For a given strength of selection, genetic load is mitigated by adaptive dispersal (
) relative to the case when migration is random (black curve; 
). This result occurs because individuals move out of habitats where they are less fit, prior to experiencing the expected mortality. GDD is most effective at reducing genetic load when low fitness individuals are much more likely to disperse than high-fitness individuals (large 
). Observe that complete adaptive dispersal (
, so that 
and 
) eliminates the load entirely (red curve in panel A lies along the horizontal axis). Variance in fitness is measured before migration or selection, and load is measured during selection, after migration. Parameters: (A) 
, (B) 
, with s varying from 0 to 1 (the three dashed vertical lines correspond to s = 0.3, 0.6, and 0.9, from left to right). See Fig. S10 for the same result with different initial allele frequencies.