Habitat destruction, biological invasions, and their interaction are global drivers of biodiversity loss. New Caledonia, one of the earliest recognised hotspots of biodiversity, is threatened by both anthropogenic fires and invasive ants, but the extent to which these threats interact to cause biodiversity declines is unknown.
Because biodiversity spans several levels of organisation (from genes to communities) and relates to different attributes (compositional, structural and functional), a hierarchical approach was undertaken to address this issue, using ants as bioindicators. Ants are of great ecological importance, especially in tropical biomes, and their classification into functional groups provides a global framework for analysing their response to disturbance.
My aims are therefore to investigate the impacts of anthropogenic fires, invasive ants, and their interaction, on the native New Caledonian ant fauna at different temporal scales, and at different levels of biological organisation (community, species, genes). The study contributes to an improved knowledge of the New Caledonian ants, for example by revealing the lack of specialised subterranean species, and by investigating island-scale patterns of ant communities, in relation to habitat and invasion. The mechanisms by which fire impacts native ants, either as a standalone process or in association with invasion are identified. In particular, fire, by creating macro- and microhabitats favoured by invasive ants, facilitates invasion, which then causes further diversity declines, either in the short- (post-burning) or long-term (forest fragmentation). Major invasive ants (little fire ant and yellow crazy ant) therefore fit the model of 'back-seat' drivers of native ant biodiversity.
The hierarchical approach used enables the detection of trait-derived responses at the species and genetic level, in addition to responses measured at the community level. This study highlights the advantage of a holistic approach to investigating biodiversity-related issues.