How might the increasing isolation of the populations in these forests influence their success and evolution.?

As a result of human activity, extensive forests are becoming fragmented into small forest islands.How might the increasing isolation of the populations in these forests influence their success and evolution.?
For real changes to be seen, evolution takes at least tens of thousands of years. So the secluded populations created by humans are still a ways from providing noticeable changes.How might the increasing isolation of the populations in these forests influence their success and evolution.?
A population's success might be positively influenced if, within a given forest island, competitors and predators are excluded. Success would be negatively influenced if the island is so small or non-diverse that there are insufficient resources for a species to survive. Also, of course, if the island is too small too support a viable breeding population, success would be negatively impacted.





In terms of evolution, one key driver of change is the isolated population. If a population lacks representation of the full suite of variation within a species, and that population is unable to breed outside its island, eventually that population could become reproductively isolated from (unable to breed with) the larger population. Once that reproductive isolation occurs, by definition a new species is formed, and further evolution might be expected.





While on the face of it, it is reasonable to assume that evolution wouldn't occur in human time scales, it is important to remember that some species have extremely short reproductive cycles, and are capable of multiple generations per year. Would one expect to see evolution in a large mammal species that produces a new generation only once in 5 years in this example? Probably not. But what about beetles, or bacteria, or fungi? Evolutionary pressures in those species might be expected to have a more rapid impact.