Ecological Biogeography of Plants on Islands

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Most island biogeographic studies suffer because they lack information on island habitats relative to mainland sites and they record only species presense-absence rather than density. In a limited number of previous studies, plants have been shown to have high immigration and low extinction rates on continental islands generally, and hence such islands are relatively species rich with low endemism. This study proposes to extend work begun in 1981 on the plant diversities, densities, and distribution on islands in Barkley Sound, Vancouver Island Canada. The new research will examine plant distributions as functions of habitat availability on various islands, turnover dynamics as functions of both biotic and abiotic factors on islands, and the short-term population and evolutionary consequences of the more dynamic species in the system. With a range of 185 islands from inshore rocks to over 30 km distant from "mainland", varying in size over 5 orders of magnitude, and with a very diverse flora with widely different growth forms, habitat requirements, dispersal and reproduction dynamics, the Barkley Sound system is ideal for a closer examination of many of the questions that currently cause dissent among ecological biogeographers. Proposed research will focus on habitat definition and quantification, classification of habitat quality for plant species, assessing the causes of species turnover, quantifying dispersal variables in two plant groups, soft-fruited species that are bird-dispersed and parachuted species that are wind-dispersed, and examining the effects of herbivory on colonization and the evolutionary consequences of island life to dispersal-related morphology and herbivore resistance.