Factor | Expected effect on genetic variability in affected populations | Population process |
---|---|---|
Geographic marginality | negative | Drift by increased population turn-over and low population density because of unfavourable environmental conditions |
Gene-flow | positive | Gene-flow counteracts the effects of drift |
Mixed mating system | negative | Selfing decreases effective population size and thus increases drift |
Environmental marginality | negative | Drift by increased population turn-over and low population density because of unfavourable environmental conditions |
Biotic interactions | negative or positive | Drift by increased population turn-over due to interspecific competition Introgression of alleles from related species by hybridisation |
Dispersal barriers | positive | Accumulation of immigrating alleles |
Range expansions | negative | Drift due to founder effects, bottlenecks or allele surfing |
Population fragmentation | negative | Drift due to diminished effective population size |
Secondary contact | positive | Mixing of alleles that evolved in isolation |