Urbanisation factors impacting on ant (Hymenoptera: Formicidae) biodiversity in the Perth metropolitan area, Western Australia: Two case studies

Two synchronous projects undertaken in 2011 examined the likely impact of increasing urban densification on invertebrate populations within urban settlement in Perth, Western Australia. One project analysed the ant fauna found in 20 gardens and lawns in small to very small properties (these having a bungalow or duplex (semi-detached) as the main residential building, and a lawn or garden area of 43 m²–332 m²) east, south, north and west of the Central Business District (CBD). The other project examined the ant fauna at 14 sites, principally in native regrowth along the Kwinana Freeway, a major artery that runs north to south through Perth’s suburbs. The gardens and lawns produced a very depauperate fauna of 26 ant species, of which a maximum of 20 were native and at least six species were exotic. The ant fauna from regrowth adjacent to the Kwinana Freeway and at two additional sites (one a bush control) was more than twice as rich, the 56 species collected including only two exotics. In the garden project, ant richness, evenness and abundance were not significantly correlated with size of the garden area. The same applied even when the exotic Pheidole megacephala-dominated gardens were removed from the analysis. Ordination analysis combining the two sets of data revealed a distinct clustering of most of the regrowth sites, whereas the bush control stood alone and garden or lawn sites exhibited a much looser pattern of association. We suggest that increasing the density of Perth suburbs is resulting in drastic loss of native invertebrate fauna, of which ants are a useful bioindicator. However, native vegetation regrowth along major arterial roads could act as a reservoir for invertebrate species that might otherwise disappear entirely from the Perth metropolitan area.