Recovery of indigenous butterfly community following control of invasive alien plants in a tropical island’s wet forests
Invasive alien species pose one of the highest threats to biodiversity, especially in isolated oceanic islands where high rates of both endemism and extinction risk also usually prevail. Few studies have investigated the impact of invasive alien plants on butterflies in insular ecosystems, despite butterflies representing a key indicator group for terrestrial arthropod diversity. Using the Pollard Technique, we quantified butterfly species richness and abundance in eight wet lowland forest areas invaded by alien plants, principally the strawberry guava (Psidium cattleianum Sabine) on the tropical volcanic island of Mauritius, and compared the results with paired adjacent forest plots that had been weeded of alien plants between 2 and 12 years previously. Butterfly assemblages in weed-infested and weeded forests were distinctly different with higher species richness and much higher butterfly abundance in the latter. At least some of these differences seemed attributable to weed removal effects on forest structure, but understanding the precise mechanisms involved will require further study. The results suggest that alien plant invasion may have contributed to the extinction of certain endemic taxa and can increase the likelihood of butterfly species extinction by reducing population sizes through reduced habitat quality. Such a shift in a forest’s butterfly assemblage is likely to have negative effects on both their indigenous predators and the plants they pollinate. It is argued that in order to maintain butterfly and other arthropod diversity and function in these forests, alien plant control must be maintained and extended beyond the current 1% of surviving forest remnants.