Gene flow can evolve. ~ American botanist Norman Ellstrand
Gene flow is the transfer of genes from one population to another. Thanks to airborne pollen delivery, and from pollinators, gene flow is more frequent in plants than animals. Plants exchange genes at considerable distances: hundreds or thousands of meters. One fig tree was found to have its paternal sire 85 km away.
Physical barriers impact gene flow, as can less tangible hindrances. In animals, female sexual preferences are instrumental in limiting gene flow.
Plants seldom have such inhibitions. Generally, hybridization is less restrictive in plants than animals, as plants are more flexible genetically and cognizant of what may be reproductively viable or not.
Gene flow acts as a cohesive force in uniting species. While gene flow is biodiversity in reverse, it may also provide adaptive opportunities that otherwise might be forgone.
Horizontal gene flow is thus both a homogenizing and a diversifying force. It typically involves groups of organisms that preferentially exchange genetic material. ~ Thane Papke & Peter Gogarten
Whereas proximity engenders gene flow, isolation dims it. Fragmenting forests lessen the prospects for biodiversity by segregating populations.
Genetic exchange groups appear to be the basis of many lineages observed in prokaryotes and are initiated or extinguished by sharing a common spatiotemporal existence with other exchange groups. Many prokaryotes, including pathogens, soil, and marine dwellers, use quorum sensing to regulate gene exchange. ~ Thane Papke & Peter Gogarten