DISPERSAL AND SPECIATION OF SKINKS AMONG ARCHIPELAGOS IN THE TROPICALPACIFIC-OCEAN

We examined the potential effects of geography on the distribution and speciation of skinks on tropical Pacific archipelagos. The entire tro pical Pacific skink fauna was divided into continental (found also in continental areas), Pacific (endemic to the study area but found withi n more than one archipelago) and endemic (found within only one archip elago) species categories. The number and proportion of skinks within each species category were determined for each of the 27 archipelagos in the study area. Nine geographic variables reflecting archipelago si ze, isolation and elevation were estimated for each archipelago. Princ ipal components analysis was used to reduce the nine variables to thre e uncorrelated composite variables that were interpreted as representi ng archipelago size, isolation and elevation. Numbers and proportions of skinks in each category within an archipelago were related to the c omposite geographic variables using multiple linear regression analysi s. Archipelago size and isolation were important predictors of both sk ink diversity and endemism. Results were then compared to diversity an d endemism of birds within the study area. Skinks showed an archipelag o-wide level of endemism similar to that of birds. On an archipelago b y archipelago basis, however, large differences between birds and skin ks were evident. In particular, the New Caledonia skink fauna was much more endemic than that of birds. The bird faunas of Hawaii and the Ma rquesas were nearly completely endemic, while no endemic skinks occurr ed in these two archipelagos. These differences presumably reflect the relative dispersal powers of skinks and birds and, consequently, rate s of colonization and speciation. Differences may also be due partly t o morphological conservatism among isolated skink populations and the occurrence of cryptic species that have not yet been identified as sep arate species. The discovery of such cryptic species, however, is unli kely to increase the endemic skink fauna of Hawaii and other distant a rchipelagos to a level commensurate with that of birds. Differences in endemism between skinks and birds may also be due to unknown local ec ological interactions.