Aires protégées et invasions biologiques : le cas de la fourmi Wasmannia auropunctata (Roger) en Nouvelle-Calédonie

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The tramp ant Wasmannia auropunctata (Hymenoptera, Formicidae) invaded New Caledonia around 1970. Though it was first supposed to be restricted to disturbed areas, the invader colonized a diversity of native biota. Its occurence was especially noticed in protected areas where the vegetation has a great value for conservation. The invader thrives in sclerophyll forests where it may even saturate the biotope. This raises much concern, as this type of forest is now restricted to relicts and is considered as the most valuable biotope to be preserved in New Caledonia. The invader has been less obvious in the dense humid forests on ultramafic rocks, which sup¬ ported for some time the idea of an ecological resistance to invasion in this forest. But recent studies indicate the steady progress of Wasmannia and its ability to permanently and efficiently colonize these biota. Wasmannia is primarily a litter-dwelling ant and most of its action has been monitored at this level. The domination of the invader on the native myrmecofauna is absolute in localities where it is able to build large populations. II also eliminates a significant part of the arachnofauna and its impact can be observed even on vertebrates like skinks and gekkos. This opportunistic ant also forages in the canopy where its impact on the native fauna is more difficult to assess. Wasmannia auropunctata is a successfull invader because it shares most characters common to the functionnal ant species group known as « tramp species », which are perceived as pests everywhere in the world. In New Caledonia, no native species seems able to compete with Wasmannia and interfere with its colonizing success, as this ant is a very efficient fighter and also is able to adapt its nesting behaviour to adverse situations. But the main problem is the difficulty to change human behaviour, as people are still the most active and efficient agents of the ant displacement and extension.