Numbers of plant species on the islands of Aldabra Atoll

Abstract

The logarithm of island area accounts for 70 % of the variance in the number of plant species occurring on 100 lagoon islands. Two components of island altitude (altitude of the island rim and the logarithm of the island’s inland altitude) are also of importance, and account for 9 % of the variation in species numbers. A further 13 variables account for only an extra 5 % of the variance in the mixed model. These results resemble the findings of other island studies. In the equation S = K A z , z = 0.345 and falls within the range of expected values. The species-area curve gives little indication of the ‘small island effect’ found for other small islands; this may reflect, among other factors, the richness of the Aldabran flora when compared with those of the small island ecosystems already studied. The curve is also compared with that compiled by Williams (1964) and a discrepancy between the two is discussed. Woody plants are largely responsible for the increase of species numbers with increasing area. Species that are restricted to islands of particular sizes are listed and the characteristics of the frequencies of occurrence of the more common species are summarized.