Number of endemic and native plant species in the Galapagos Archipelago in relation to geographical parameters

By simple and multiple regression analyses we investigate updated species numbers of endemic and native vascular plants and seed plants in the Galapagos Archipelago in relation to geographical parameters. We find that the best models to describe species numbers are regression models with log-transformed species numbers as dependent and log-transformed modified area (i.e. area not covered with barren lava) as an independent variable. This holds both for total species number, for native species number, for endemic species number and for total number of seed plants as well as number of endemic seed plants. For the ratio between endemic and native species, modified area is also the major significant variable, but with a negative regression slope. Multiple regression models show that some isolation measures are significant contributors and may explain some of the residual variation, but their contribution to total explained variation is in general small. The results show that the species area relationships are different for native and endemic species. This is discussed in relation to classical island biogeographical models, and the concepts of radiative speciation.