Resource Use and the Survival of Land and Freshwater Vertebrates on Oceanic Islands

Land and freshwater birds and mammals reduce resource use on small oceanic islands. The adjustments used vary among taxa. Rails reduce energy expenditure both by a decrease in body mass and the evolution of flightlessness. Island ducks have responded principally through a reduction in body mass. Bats minimize expenditures by having a small mass, consuming fruit, and often experiencing a direct decrease in the rate of metabolism. Most pigeons reduce energy expenditure through a direct decrease in metabolism and the consumption of fruit. Rodents reduce energy expenditure directly and through a decrease in mass. Reduced resource requirements by individuals permit larger populations, which in turn increases the probability of population survival. On many islands ectotherms have replaced endotherms as herbivores and carnivores; the great reduction of resource use associated with this shift has permitted ectotherms to have both large populations and a large body size. High rates of resource use occur in populations that consist of individuals that are endothermic, large, or highly active, or have unusually high costs of maintenance. These are the species that are least likely to survive on small oceanic islands and habitat "islands" produced on continents by human activity.