UCB Moorea Class: Biology and Geomorphology of Tropical Islands

This study aims to determine and compare survivorship of two populations of Sophora tomentosa (Fabaceae) on Mo'orea, French Polynesia. The two populations studied were on separate reef islets, or motu. One population, on the motu Tiahura, appeared healthy while the population, on the motu Fareone, appeared distressed. The life cycle of S. tomentosa was broken into four life-stages: developing seed, mature seed, immature and mature plant. The three parts of this study are designed to determine the percent survival between each of these four life-stages and address some of the potential factors effecting survivorship at each transition. To assess survival of developing seeds and the impact of insect granivores, seedpods were collected from each population and the seeds were inspected for evidence of insect damage. The rate of granivory was shown to be significantly higher than expected in the Fareone population, while it was shown to be significantly lower than expected in the Tiahura population. Seeds not attacked by insects were germinated in six different soil conditions to assess the likelihood of mature seeds becoming young plants. In the germination study the impact of leaf litter from an introduced tree, Casuarina equisetifolia (Casuarinaceae), known to have allelopathic properties, was specifically examined. The germination data show there to be no significant difference between the treatments. To determine the ability of young plants to survive to maturity, the percentage of sexually mature plants within each population was used as a proxy for survival. Using this proxy, no significant difference in survivorship between the two populations was demonstrated. The findings of this report suggest that the insect community, some members of which are introduced species, is having a significant impact on this native plant population. Overall survivorship was greatly diminished in the Fareone population other factors believed to be impacting the population as well, but they are not investigated in this report