1. Dobson & Hildrew (1992) enhanced leaf litter retention in four streams by placing small plastic leaf traps in manipulated stretches. Litter standing crop and the local abundance of shredders was increased, relative to control stretches, in all sites save one which was naturally highly retentive. These results could indicate food limitation in these detritivores, but might have occurred in response to an altered hydraulic regime or increased habitat availability.
2. Shear stress was characterized in the four streams manipulated by Dobson & Hildrew (1992). This was carried out on three occasions in both the manipulated and control stretches of each stream. While there was evidence that the manipulation of retention did influence near-bed flows, these changes were not consistent enough to explain the response of shredding invertebrates to experimental manipulation.
3. In a further experiment, we exposed real and artificial leaves to colonization by invertebrates. Shredders, collectors and predators all colonized real leaves in preference to plastic substitutes.
4. These results support the hypothesis that detritivorous macroinvertebrates exploit aggregations of leaf litter primarily as sources of food, rather than as habitat or habitat modifier.