Migration load when there is frequency-dependent competition between residents and immigrants: Combining genetic and demographic dynamics

Background/Question/Methods

Immigration of maladapted alleles typically opposes the effect of local selection, resulting in a migration load. Demography is known to be important to migration load in cases of asymmetry in population size or dispersal. Demography could also affect migration load when competition for limiting resources between similar phenotypes is stronger than when between dissimilar phenotypes (frequency–dependent competition). We combined a demographic and a quantitative genetic model to quantify the effect of frequency–dependent competition on migration load and population size in populations connected by dispersal and subject to divergent selection.   

Results/Conclusions

Frequency–dependent competition reduces migration load when density–dependence occurs before selection, even when populations have identical carrying capacities and migration rates. When selection is relatively strong however, frequency–dependent competition increases migration load, especially when selection occurs before density-dependence and after migration. Frequency–dependent competition reduces competitive interactions between resident and immigrant genotypes and generates a form of negative frequency–dependent selection, which alters the efficiency of local stabilizing selection at preventing migration load. Our result adds new dynamics that illustrate why the interaction between demography and genetics is critical to understand population dynamics in variable environments