What are the intrinsic causes of the limits to adaptation throughout a species' range and at its edge? I give an introduction to the problem, and provide some results on the evolution of clines in allele frequencies due to drift, selection and migration:
Random genetic drift shifts clines from side to side, alters their width, and distorts their shape. The wobbling in position makes the expected cline wider. However, locally, drift drives alleles towards fixation, so individual clines can often be narrower. I show that the relation between the deterministic cline width, expected cline width, and width of the expected cline is driven by the average standardized variance of local allele frequencies.
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