POPULATION-DENSITY AND DISPERSAL ABILITY IN DARWIN DARKLINGS - FLIGHTLESS BEETLES OF THE GALAPAGOS-ISLANDS

This study is the first to combine both field and genetic data to exam ine population structure in flightless beetles from the Galapagos Isla nds. Field studies were conducted on four species of tenebrionid beetl es belonging to three genera, Ammophorus Guerin-Meneville, Blapstinus Latreille, and Stomion Waterhouse. The dynamics of the beetle communit y at the study site, Tortuga Bay, Santa Cruz Island, were analyzed in an attempt to examine patterns of activity and to quantify species abu ndances, population sizes, densities and levels of individual vagility . Beetle activity was found to vary with temperature, precipitation an d number of sunlight hours. Although the number of recaptures was low, densities in the quadrats ranged from eight B. lugubris Boheman per h ectare to 1238 S. laevigatum Waterhouse per hectare. Individual vagili ty is shown to be low among S. laevigatum, the most abundant species a t the study site, as the dispersion index (DI) showed that captures we re aggregated in three of the four quadrats, suggesting little movemen t. In addition, beetle captures occurred more frequently than expected in internal traps, again revealing limited movement into or out of th e quadrats. These results were confirmed by a separate analysis of gen etic differentiation among demes of S. laevigatum which showed the num ber of migrants to be less than one per generation.