Diversity and Abundance of the Fauna in Yuccabine Creek, a Tropical Rainforest Stream

Abstract

This contribution introduces a long-term study of Yuccabine Creek, an order-3 upland rainforest stream situated in tropical Queensland, at about 18°S. and at 600 m altitude. The stream is rocky and comprises alternating riffles and pools. It is acidic (pH 5·9–6·9), with low conductivity (33–70 μS) and seasonally variable temperature (10·5–25·0°C) and discharge (0·02–1·00 m3 s-1), reflecting the regional climate of hot wet summers and warm drier winters. In comparison with streams elsewhere, the invertebrate fauna is diverse: currently, 267 species have been recognized from one 50-m stretch of riffle. Of these, 245 are insects, including 65 species of Chironomidae, 59 of Trichoptera and 45 of Coleoptera; but some taxa are apparently not unusually diverse, e.g. eight species of Plecoptera, 16 of Ephemeroptera and 12 of Odonata. From a year’s regular sampling (total of 198 1/16-m2 sample units) 211 invertebrate species were collected, although 56 of these occurred only once. Only two species of fish occur. Data on diversity, abundance and variability of samples are summarized for a full year, but patterns of change are not considered here. The mean number of taxa collected per month was 105 (range 85–134), and the mean monthly abundance per square metre was 2768 animals (range 1520–4240). Variability of samples was usually high, indicating patchy distributions of all but the commonest species. Preliminary analysis shows that the fauna is dominated numerically and in number of species by detritivorous collectors, with smaller numbers of predators, grazers-scrapers, filterers and shredders. Yuccabine Creek does not have the constancy of conditions associated with the wet equatorial tropics; however, it probably does represent a common type of system to be found in the geographically widespread wet but seasonal tropics, and it reflects the highly seasonal pattern generally reported for Australian streams. The diversity and organization of the community in Yuccabine Creek are discussed in the light of current ecological ideas; seasonality of the stream is a major factor in determining the composition of its fauna.