∞ generated and posted on 2016.09.06 ∞
Reductions in populations to very few breeding individuals, potentially resulting in genetic drift.
I use the word "potentially" because genetic drift, being stochastic (that is, random), only happens with a certain likelihood rather than with certainty (flip two coins and only half the time you will come up with something other than one head and one tail).
Contrasting genetic bottlenecking, founder effects – as an alternative mechanism potentially resulting in genetic drift – can occur when a new population breaks away from a main population, with this new group "setting up shop" geographically elsewhere.
Also contrasting genetic bottlenecking, founder effects tend to occur only over a single generation, the generation during which the main group is sampled to form the new group. Any subsequent genetic drift in this new group, should it remain small in size, would be attributable to genetic bottlenecking.