Research

Lizards of New Caledonias sclerophyll forests and the threats posed by the indroduced Little Fire Ant Wasmannia auropunctata

Hervè Jourdan, Jean Chazeau, Ross A. Sadlier and Aaron M. Bauer

• Introduction
• Survey of the lizard fauna in sclerophyll forest at Pindaû
• Survey of the lizard fauna in sclerophyll forest at Tia
• References

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Introduction

Among New Caledonian natural habitats, sclerophyll forest is recognised as the most threatened, now occupying only 3% (100 km²) of its original range. Sclerophyll forests (dry rainforest) are restricted to small patches on the dry west coast of the main island, below 300 m elevation where annual rainfalls reach less than 1100 mm. It may be characterised as a dense formation with a 15 m high canopy, or an unstratified understory, with a high contribution of vines (near 20% of the flora).

Among the threats to the New Caledonian biota is the spread of exotic species through human activity. One of the most 'successful' invasions has been the rapid spread of the Little Fire Ant Wasmannia auropunctata onto the archipelago. This tiny stinging ant (worker ants are 1.5 mm in length) was first identified in New Caledonia from Dumbea in 1972. It is a representative of the "tramp ant" group which exhibit biological characteristics (unicoloniality, polygyny, opportunism for food and nest location) that have facilitated its spread in the tropics through a dispersion via human activities.

We have undertaken collaborative research aimed at documenting the lizard fauna of sclerophyll forests and the potential impact of the invasive ant Wasmannia auropunctata on that fauna. To date two studies have been undertaken, one on the Pindaû Peninsula on the northwest coast of the island south of Pouembout, and the other at Tia in the Pouembout Valley.

The decline in abundance of certain lizard species observed in Pindaû and Tia is consistent with previous inferences of a decline of gecko populations through the spread of the Little Fire Ant on the northeast coast of New Caledonia.

The way in which Wasmannia auropunctata impacts upon the lizard fauna is unclear but probably occurs as direct predation, and/or monopolisation of resources (food or shelter) or both of these. In New Caledonia, there is evidence that in invaded places, the Little Fire Ants is altering native arthropod communities. In an invaded sclerophyll patch a lowering of 60% of overall arthropod abundance at the ground level, and 20% at the canopy level has been observed. As such there is the potential for both:

• competition for prey between Wasmannia auropunctata and native lizards
• and a lowering of arthropod availability (resulting in lowering of the carrying capacity of sclerophyll habitat).

The data obtained from our studies raise the question of maintenance of natural communities (herpetofauna and otherwise) in New Caledonia in a long term perspective. The process of invasion has been rapid in New Caledonia and an impact upon the native fauna is already noticeable. The spread of this ant represents a major and immediate threat to the rich endemic New Caledonian lizard fauna, and for the whole native fauna - it may be the most threatening exotic species ever introduced into New Caledonia.

Copyright © Australian Museum, 2002