∞ generated and posted on 2016.11.04 ∞
Possible location within which the majority of evolutionary divergence as well as the first steps of speciation occur for obligately sexual species.
Peripheral isolates, as the term implies, are found isolated on the periphery of larger populations. They potentially are subject to different selective pressures and, because of their location, are most likely to become cut off from the larger population due to the formation of geographical barriers or, instead, due to a shrinking of the range of the larger, parental population.
It is important to keep in mind that a given population may have multiple peripheral isolates. Furthermore, those peripheral populations are not necessarily long lasting but instead should be prone towards extinction since they are both small and exist on the fringes of the range of the larger population. That is, they may be both subject to the strongest hard selection and, in terms of genetic variation existing within the population, as well as simply population size, may be least well prepared to deal with it.
This tendency to go extinct includes once such populations are fully allopatric and completely cut off from their parent population. Nevertheless, peripheral isolates are at least a good way of thinking about the first steps down the road to towards allopatric speciation, with numerous peripheral isolates potentially generated by species but few of which actually giving rise to new species.
Note that peripheral isolates and subspecies have a bit in common, though with subspecies populations in this scheme likely substantially larger than the population sizes as may be envisioned for peripheral isolates. On the other hand, should the overall range of a species contract such that subspecies populations become both smaller and cut off from other members of the same species, then essentially these subspecies would be playing an equivalent role to that of peripheral isolates.
This scenarios considering subspecies is one that potentially heads down the road towards eventual allopatric speciation. More specifically, it can be viewed as what is known as peripatric speciation.