KOMDEUR J (1997) Dutch Ornithological Union: Theme Day Effects of habitat fragmentation on birds and mammals: Genetic variation and demography in isolated Seychelles Warbler populations.. LIMOSA 70 (1): 40-40.

The degree of isolation and sex ratio variation of adults in small populations can have a major impact on the preservation of genetic diversity. Genetic drift and inbreeding may cause the loss of genetic variation and an increase in homozygosity. I will address these perspectives in the Seychelles Warbler Acrocephalus sechellensis. Between 1959 and 1968 the world population consisted of only 30 birds entirely confined to Cousin Island (29 ha) in the Seychelles. Through conservation actions the population has now reached carrying capacity of c. 320 birds, but 25 years after the population bottleneck the genetic variation (examined by DNA fingerprinting) is low. After 1988, additional breeding populations were established on the islands of Aride (68 ha) and Cousine (26 ha), each originating from 29 birds. Small population size and low genetic variation had no negative effects on reproductive success in the new populations. The Seychelles Warbler shows enormous skews in sex ratios of offspring at birth, varying from mainly males on low-quality territories (as measured by food availability) to mainly females on high-quality territories. Young females frequently remain in their natal territories as helpers. Thus, breeding birds avoid having competing 'helpers' on low-quality territories and enhance their fitness by producing helpers (females!) on highquality territories. Also on Aride Island, with highquality territories, more females were produced. The mating system changed from monogamy towards polygyny, thereby changing effective population size.

[free pdf] [dutch summary]