The importance of genetic variation for the viability of small avian populations the Seychelles Warbler and the African Marsh Warbler

Nowadays, many natural populations have to face up to problems such as gene tic drift and 'forced' inbreeding as a result of reduced numbers and popula tion isolation. This is thought to have a major effect on their survival. R esearch on the isolated Seychelles warbler showed that fitness parameters a n not negatively affected by a high inbreeding Frequency and a low level of heterozygosity. However, one has to be careful to translate these results to other isolated species. It is hypothesised that the effect of 'genetic e rosion' on fitness may be less disastrous for island species, which are use d to go through narrow population bottlenecks. as compared to continental s pecies. Conservationists should be aware of these differences between speci es and of the fact that the long-term prospects can be reduced by lack of a daptive genetic potential.