Butterflies and day-flying moths in a fragmented urban landscape, south-west Western Australia: patterns of species richness

Surveys of butterflies and day-flying moths were conducted at 46 bushland remnants in the Swan Coastal Plain, Western Australia, between 2001 and 2005. A total of 17 075 individuals was recorded, representing 35 butterfly and 5 day-flying moth species. Individual site species richness varied between one and 27 species. Two main groups of taxa were identified: (i) species that are reliant on remnant native vegetation for breeding and are entirely or predominantly restricted to remnant bushland (resident species or urban avoiders, 27 taxa); and (ii) species that now breed primarily on introduced plants and disperse readily through the urban matrix, but which also visit remnant bushland and sometimes breed there (non-resident species or urban adapters, 13 taxa). Estimated species detectability varied widely between species and seasonally, but for most taxa was consistent across the three years of the study. Peak detectability was strongly related to observed abundance, something that is well known (intuitively), but has rarely been demonstrated (quantitatively). Only one listed endangered species was recorded, the Graceful Sun-moth Synemon gratiosa which was observed in low numbers at six sites. Several species were encountered less frequently, although these have populations outside the region. Few of the surveyed remnants were considered to have an intact butterfly fauna; it is inferred that the majority had lost some or all of their original resident species. The reliance of many species on specific host plants, and the ability of some to adapt to introduced weeds, are important factors in their persistence within remnants. These bushland remnants are effectively habitat islands for butterflies and day-flying moths, and the few remaining species-rich bushlands are therefore of regional importance for conservation of this group. This paper serves as a baseline study against which to monitor any future changes to the butterfly fauna of these remnants.