The Founder effect:
Genetic drift likely when a few individuals colonize an isolated island or patch of new habitat. The smaller the size population the less genetic diversity that will be present in that gene pool. Contributed to the evolutionary divergence of Darwin's Finches on the Galapagos.
The Population Bottleneck:
A disaster such as a fire, hurricane, or earthquake reduce the size of a population drastically, killing many unselectively. The resulting genetic makeup of the left over population is not representative of the original population, leading to a bottleneck. Bottlenecking and genetic drift usually reduce the genetic variability b/c the alleles for at least some loci are like to be lost from the gene pool. Ex) northern elephant seals passed through a bottleneck after excessive hunting in the 1890's.
The difference between the two is in a founder effect there is a strong element of randomness.
What the genetic consequences of a small population?
- lose genetic diversity over time