Factors and processes shaping the population structure and distribution of genetic variation across the species range of the freshwater snail radix balthica(Pulmonata, Basommatophora)

Table 1 Factors potentially influencing distribution of genetic variation across species ranges, their expected effect on genetic variability and the acting population processes.

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

ISSN: 2730-7182