UCB Moorea Class: Biology and Geomorphology of Tropical Islands

Classical biological control aims to actively manage threats that cause immense losses in biological diversity. The introduction of a biological control agent Colletotrichum gloeosporioides f. sp. miconiae (Cgm) in April 2000 to Tahiti, French Polynesia was intended to control the massive spread of an invasive weed Miconia calvescens. However, while Cgm has subsequently spread to Mo’orea, its impact on reducing M. calvescens remains uncertain. The main objectives of this study are: (1) to quantify the amount of the fungal pathogen infecting the M. calvescens plants at three elevation ranges on Mo’orea, (2) to understand the impact of moisture on the proliferation of disease development, and (3) to test the influence of endophytic fungal communities on the competitive ability of Cgm. Results from quantifying leaf damage showed that at higher elevations, Cgm disease development is more rampant. In laboratory experiments, varying moisture did not significantly affect the health of the seedling. While Cgm growth rate correlates with competitive ability, endophytic fungal growth rate does not, leading to speculation that other modes such as chemical interactions allow for endophytic competitive ability. Lastly, data supports the hypothesis that Cgm becomes a better competitor against the endophytic fungal species at higher elevations. Results of this study suggest that other microclimatic factors such as temperature and humidity may play a role in disease development. While Cgm may decelerate the growth of M. calvescens, Cgm alone is not likely to obliterate the massive damage M. calvescens has done on the native flora of Mo’orea and its surrounding islands. Conservation biologists must urgently attack this pest, or the fragile ecosystem of the islands will lead to massive losses in biological diversity.