It is often easier to assess such ecological processes as the effects of invasive species by focusing on a small, insular macrosystem like that of the island of Mauritius in the Indian Ocean. The Pink Pigeon (Nesoenas mayeri) was once widely distributed throughout Mauritius, but by 1990 only 10 individuals were left. The introduction of such non-native mammalian predators as the Crab-eating Macaque (Macaca fascicularis), the mongoose (Herpestes auropunctatus) and feral cats contributed to the catastrophic decline of this pigeon, which had no defense against these invaders. The introduction of non-native plants has played a role, as well. Exotic weeds such as Chinese Guava (Psidium cattleianum) and the privet Ligustrum robustum var. walkeri have invaded and choked the forest habitat these pigeons favor, inhibiting the regeneration of native seed-bearing plant species upon which the pigeons forage. (On the other hand, introduced Japanese Red Cedars (Cryptomeria japonica) provide ideal nesting sites for the pigeons, and the entire wild population nested in these trees during its nadir.) Fortunately, the threats posed by these invaders--along with habitat loss to human activity—have been lessened somewhat: Successful conservation efforts have lead to a rebounding population of these beautiful birds, which now numbers around 400 individuals. The demise and fluctuating resurgence of the Pink Pigeon could help researchers better understand the impact of invasive species, the definition of harm, and the point at which costs or risks should trigger action on other islands and mainland systems as well.
The artist made this watercolor after her visit to Mauritius in 2009.