Figure 3.

A model shows that peripheral populations of a species can expand with the establishment of a locally adapted inversion. Top: In the capture scenario, alleles adapted to the range periphery (to the right of the vertical dashed line) are present before the inversion appears. The equilibrium population density (shown in dark gray) is slightly depressed below carrying capacity by recombinant genotypes. The inversion then captures those alleles and becomes established at the periphery, which causes the population density to increase to the carrying capacity, K (small arrow). Bottom: In the adaptive cassette scenario, the locally adapted alleles are initially absent. Populations in the periphery are maladapted and far below carrying capacity. With the introgression of an inversion that carries the locally adapted alleles, the densities increase greatly and the range expands outwards (large arrow). From Kirkpatrick and Barrett (Kirkpatrick and Barrett 2015).