Using ants to monitor changes within and surrounding the endangered Monsoon Vine Thickets of the tropical Dampier Peninsula, north Western Australia

Abstract

The 79 naturally fragmented and localised Monsoon Vine Thicket (MVT) patches on the coast of the Dampier Peninsula, Kimberley region, Western Australia, are listed as: a culturally significant ‘Threatened Ecological Community’ (TEC), ‘Endangered’ under the Commonwealth (EPBC Act, 1999) and ‘Vulnerable’ under Western Australian legislation. Fire and introduced species are significant disturbance factors affecting the MVT patches. Focussing on five patches, this study aimed to: assess ant diversity and composition; determine relationships between environmental variables, fire history and invasive ants; determine the value of ants as bioindicators of environmental change; and involve indigenous communities in planning and data collection. Three habitats, inside (I) and edge (E) of five MVT patches (11 ha–56 ha) and immediately outside (O) in the surrounding Pindan woodland (PW), were sampled over two seasons; 7,342 ants from 7 subfamilies and 81 species were collected by pitfall trapping and hand collecting. A gradation of species richness from I (37 spp.), to E (48 spp.), to O (62 spp.) occurred, reflecting trends in environmental variables of decreasing litter volume, litter depth and canopy cover, and increasing fire frequency across habitat types. NMDS ordination identified a separation of ant composition between I, E and O, while CCA revealed a clear separation between I, E and O driven by litter volume and depth, canopy cover and fire history.Distinctly different ant assemblages were found within the MVT, with species inside being those that prefer cool relatively dense vegetation and those at the edges preferring more open habitat. The degree of openness of the edge of the MVT edges is related to fire frequency, while species within the PW were typically arid-adapted species that prefer a more open habitat. Two invasive ant species, namely Paratrechina longicornis and Monomorium destructor, were found to be present in the patches and, in common with many invasive ant species, P. longicornis was characterised by high numbers, comprising 43% of total individuals across the study. As little data previously existed on the ant communities of the dry MVT patches of the Dampier Peninsula, the results add significant new information on the ant fauna of the MVT patches and illustrate how using ants as bioindicators can assist interpreting the impact of fire, invasive organisms and management on the conservation status of MVT patches. This study also serves as a model for collaborating with indigenous people to undertake data gathering, interpretation and management of such areas.