Abstract
The mature palm forest of the Vallée de Mai, a UNESCO World Heritage Site, on the Seychelles island of Praslin, is a unique ecosystem containing many endemic species, including the iconic coco de mer palm Lodoicea maldivica. In 2009, the invasive yellow crazy ant Anoplolepis gracilipes was recorded for the first time within the palm forest, raising concern about its potential impacts on the endemic fauna. This research aimed: (1) to assess the current distribution and spread of A. gracilipes within the palm forest; (2) to identify environmental variables that are linked to A. gracilipes distribution; and (3) to compare endemic species richness and abundance in A. gracilipes invaded and uninvaded areas. Anoplolepis gracilipes was confined to the north-east of the site and remained almost stationary between April 2010 and December 2012, with isolated outbreaks into the forest. Infested areas had significantly higher temperature and humidity and lower canopy cover. Abundance and species richness of the endemic arboreal fauna were lower in the A. gracilipes invaded area. Molluscs were absent from the invaded area. The current restricted distribution of A. gracilipes in this ecosystem, combined with lower abundance of endemic fauna in the invaded area, highlight the need for further research to assess control measures and the possible role of biotic resistance to the invasion of the palm forest by A. gracilipes.
Highlights
Ants are highly successful invaders, on islands (Ingram et al 2006; Cerdá et al 2012)
Anoplolepis gracilipes has occurred across Praslin for at least the last decade and is present in Praslin National Park, there were no reports of the species occurring inside the Vallée de Mai until 2009
Despite its documented ability to rapidly cover large areas in high densities under optimal conditions (Hill et al 2003; O’Dowd et al 2003), the current distribution of A. gracilipes in the Vallée de Mai appears to be in a dynamic equilibrium and is restricted to the north-east of the reserve, with highest activity levels close to the firebreak and the visitor centre
Summary
Ants are highly successful invaders, on islands (Ingram et al 2006; Cerdá et al 2012). Their invasion is of concern to conservationists due to their broad range of impacts (e.g., Holway et al 2002; O’Dowd et al 2003; Lach and Hooper-Bui 2010) and the difficulties of eradicating them once established (Silverman and Brightwell 2008; Hoffmann et al 2011). Despite control measures on Mahé, its range across the Seychelles islands has expanded and, by 2000, the species occurred on nine of the central islands, including Praslin (Hill et al 2003)
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