Factors Affecting the Number of Species of Plants on Islands of the Great Barrier Reef, Australia

A survey of eighty-two cays and ten continental islands of the Great Barrier Reef and Torres Straits, Australia, yielded 603 species of ferns and flowering plants. The numbers of species on islands were multiply regressed, separately for cays and continental islands, against seven independent variables: latitude, longitude, insular area, insular height, rainfall, distance to mainland and distance to nearest larger land mass (whether mainland or another island). The most important variables predicting species-richness were measures of insular size. For continental islands the most important predictor was insular area, whereas for cays it was insular height. Distance was selected also but accounted for such a small amount of variation as to be practically negligible. Other factors were seldom selected at