Red Crabs in Rain Forest, Christmas Island: Differential Herbivory of Seedlings

Abstract

Red land crabs (Gecarcoidea natalis), at densities up to 2.6 m-2 on the rain forest floor on Christmas Island, Indian Ocean, are important herbivores and predators of seedlings of trees and vines. In short-term exclosure experiments during the wet season with transplanted seedlings of 18 species, red crabs were the only important herbivore and selectively consumed seedlings of some species. Increasing concentrations of nitrogen, neutral detergent fiber, and total phenolics were correlated with decreased rates of grazing by red crabs. Our results extend observations of seed predation by land crabs on oceanic islands to the seedling stage and indicate that differential herbivory by land crabs may influence the relative abundance and species composition of plants in the early phases of establishment on this and other oceanic islands.