Limitations to tree seedling recruitment at Palmyra Atoll

Tree seedling recruitment is thought to be an important factor influencing forest composition and structure. In this dissertation I explore three factors that contribute to seedling survival at Palmyra Atoll in the Central Pacific Ocean: (1) how an invasion of alien rats (Rattus rattus) has influenced seed dispersal and survival, and seedling survival, (2) how invasive coconut palms (Cocos nucifera) impact native tree reproduction and growth, and (3) movement patterns of five species of land crabs. I found that rats altered patterns of tree seedling recruitment by increasing the frequency of predation on tree seeds and seedlings, and by shifting local tree seed dispersal from an interaction driven by land crabs to a directed dispersal model driven by rats. At Palmyra, introduced rats surpass crabs in the frequency of herbivore-seedling interactions, and rat impacts on seedling survival may be responsible for the structure of the atoll's current forest community. Invasive coconut palms (Cocos nucifera) also appear to negatively influence the reproduction and possibly the growth of other tree species through canopy dominance. The combined impact of rats and coconut palms has been, and continues to be a major factor shaping Palmyra's forest community. Crabs have been previously overlooked in studies of tropical forest ecology. This research reinforces the role of crabs as integral components of terrestrial systems on tropical, oceanic islands, and strengthens our understanding of how rats, as biological invaders, can have significant, lasting impacts on small island plant communities.