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The history of ants on Mauritius is a sad tale of habitat destruction and species invasions. This legacy of ecological disturbance, dating back to the 15th century, has pushed what little remains of the native ant population up to the very brink of extinction.
The alteration of Mauritius arguably began with the extinction of the dodo in 1681, 80 years after humans first arrived on Mauritius. In the centuries that followed, colonists continued to modify habitats at an alarming rate. In the 19th century, the dense Mauritian forests had been converted wholesale into tea and sugar plantations. By this time, habitat modification on Mauritius had reached almost every corner of the island.
Today, Mauritius offers a stark example of what could happen to other insular environments, such as Madagascar, if habitat destruction is left to proceed unchecked. On Mauritius, as on Madagascar, invasive plant and animal species pose major problems. Once established, invasive ants on both islands may be virtually impossible to eradicate, thus preventing the return of native ants.
Conservation practices in Mauritius are heavily biased toward preserving birds and plants, but not invertebrates. For example, land managers have established Conservation Management Areas where alien plants are manually removed up to three times per year. Actively removing large patches of weedy plants, however, creates large areas of bare soil and understory. This disturbance facilitates the establishment of invasive ants at the expense of any remaining native ants.
At present, the endemic ants of Mauritius are all confined to upland forests. One might conclude that Mauritius has few endemics, all of which live on mountaintops. On the other hand, these endemics could be the remnants of what was once a much richer endemic fauna that disappeared with the destruction of lowland forests. The recent discovery of a new genus record on Mount Le Pouce suggests that there are more species to discover on the island and that Le Pouce is a surprising sanctuary of taxonomically peculiar endemic ants. Le Pouce captures moisture from prevailing winds and clouds, enabling a native cloud-forest to grow on its slopes. The mountain contains the only significant sample of native vegetation left on the island, although they are scattered throughout dominant stands of exotics. Among the mountain?s most common habitats is a scrub of strawberry guava (Psidium cattleianum) and privet (Ligustrum robustrum). As one of the only remaining refugia for Mauritius? mountain endemics, the one-hectare forest patch on Le Pouce should receive high conservation priority.
However, if an active weeding program is initiated at Le Pouce, native ants could be eliminated from this rare patch of native vegetation. The closed vegetation is essential for the survival of the endemic Discothyrea, Pristomyrmex, and Acropya ants which thrive in the forest's cold, moist understory. With weeding, increased insolation, and regular disturbance, the invasive ants that surround this small patch would quickly move in and destroy this ant sanctuary.We are grateful to Vikash Tatayah from the Mauritian Wildlife Foundation for facilitating our visit and research, and the Forestry Service and National Parks and Conservation Service in Mauritius for permissions to conduct research in Mauritius.
Brian Fisher, Lori Lach, and Andy Suarez