Spatial and temporal variation in the macroinvertebrate fauna of streams of the northern jarrah forest, Western Australia: functional organization

Abstract

SUMMARY. 1. Spatial and temporal changes in functional organization of the invertebrate community of streams of the northern jarrah forest, Western Australia, were examined in the light of predictions of the river continuum concept (Vannote et al., 1980).2. The composition of the fauna was largely as predicted for forested headwater streams with detritivores, principally collectors, dominating the fauna. Although shredders are generally considered to be codominant in such streams, they were not abundant in the riffle areas sampled in this study.3. Some of the observed temporal changes in the composition of functional feeding groups were in agreement with those predicted by the generalized model. The abundance and richness of collectors were higher during the summer than winter, whereas the converse was true for filterers. This corresponded to the presumed availability of deposit and suspended fine‐particulate organic matter during summer and winter respectively. Scrapers and predators showed no consistent temporal pattern among sites. However, the density of the latter was highly correlated with the density of other invertebrates, particularly collectors.4. Temporal changes in the abundance and richness of shredders were not synchronized with the marked summer input of coarseparticulate organic matter. The possible reasons for this, and the role of shredders in Australian stream systems, are discussed.