Impact of habitat modification on the distribution and abundance of fruit flies (Diptera : Tephritidae) in Southeast Queensland

Loss of rainforest because of agricultural and urban development may impact the abundance and diversity of species that are rainforest natives. Tropic al fruit flies are one group of such organisms indigenous to rainforests. I n southeast Queensland, a region subject to rapid urbanization, we assessed the impact of habitat disturbance on the distribution and abundance of nat ive fruit flies. Data on four species (Bactrocera tryoni, Bactrocera neohum eralis, Bactrocera chorista, and Dacus aequalis) were gathered and analyzed over 6 months in three habitat types: suburbia, open sclerophyll forest, a nd rainforest. We also analyzed the data at a combined "dacine fruit fly" l evel incorporating all fruit fly species trapped over the period of study ( as might occur in a biodiversity assessment): these included the four speci es already named and Bactrocera melas, Bactrocera bryoniae, Bactrocera newm ani, and Dacus absonifacies. Analysis at the species level showed that the polyphagous pest species responded differently to the monophagous species. Bactrocera tryoni, which has more exotic than native hosts, was positively affected by transformation of natural habitat into suburbia whereas B. neoh umeralis, which has nearly identical numbers of native and exotic hosts, wa s found equally across habitat types. Bactrocera chorista and Dacus aequali s, each monophagous on a species-specific rainforest host plant, were most abundant in rainforest. The analysis based on the combined data suggests th at replacing rainforest with suburbia has a neutral, or even positive, effe ct on the abundance of fruit flies as a;whole. At the species level, howeve r, it can be seen that this is an erroneous conclusion biased by the abunda nce of a single pest species. Our discussion raises the issue of analyses a t supraspecific levels in biodiversity and impact assessment studies.