How does isolation affect the genetic make-up of a small population?

Laboratory studies on fruit flies and other organisms suggest that small animal populations that become isolated for long periods of time lose genetic diversity. This is an important conservation problem as the genetic diversity of a population is thought to provide the substrate on which natural selection will act to precipitate evolutionary change: a population that has lost its genetic diversity will not be able to adapt well to altered environmental conditions.

While there is solid theoretical and laboratory support for these ideas, there is little evidence for this from natural wildlife populations. In collaboration with the lab of Dr. N. Anthony (U. of New Orleans) we analyzed the genetic makeup of lizard populations surviving on 15 land-bridge islands in the central Aegean Sea. This study revealed that genetic diversity indeed declines strongly with decreasing island (and thus population) size and longer periods of isolation slowly lead to progressive loss of genetic diversity. The results suggest that in systems where fragmented populations are genetically isolated (i.e. where no individuals can cross from one fragment to the other), it is critically important to manage for large population size. In addition, in the medium- to long-term it is important to reconnect fragmented populations stem genetic losses accruing over time (see Hurston et al. 2009)