The effect of habitat configuration on arboreal insects in fragmented woodlands of south-eastern Australia

Abstract

The reduction in area of habitat patches and the concurrent increase in edge habitat associated with fragmentation of native vegetation have been shown to have a marked effect on the persistence of vertebrates in landscapes dominated by agriculture. However, because of the relatively large grain size they can distinguish, the spatial scale at which vertebrates become affected is likely to be different from that for invertebrates. Thus, although the high degree of fragmentation currently present in the sheep/wheat growing areas of Australia has been debilitating for vertebrates, this result cannot be extrapolated to the general state of species diversity. This study investigates the distribution of an arboreal insect fauna across a variety of habitat configurations common in the wheat/sheep belt of New South Wales. The aim was to determine the response of insects to habitat fragmentation at the scale associated with current agricultural practices, and to determine whether an “interior” fauna exists. Insects living on Callitris glaucophylla were sampled in the edge and interior of large state forests, in broad and narrow roadside strips and in small isolated remnants. Forest interiors had a significantly different fauna from the other four habitat configurations, and where differences between configurations occurred, interior sites tended to have fewer species and fewer individuals than the edge habitats. This result implies that the arboreal insects we studied are not adversely affected by this level of habitat fragmentation and the optimum arrangement of habitat for the conservation of insects may be quite different from that for proposed for vertebrates. However, this conclusion must be considered in the light of the dubious prognosis for long-term persistence of small habitat patches, and the possibility that fragmentation-sensitive species have already been lost from this environment.