Shredder-Collector Facilitation in Stream Detrital Food Webs: Is There Enough Evidence?

It is widely assumed that, among detritivorous stream invertebrates, shredders facilitate collectors through their role in producing particles from coarser detritus. While this hypothesis is plausible, we argue that it has not been adequately tested. It has not even been clear what information would be necessary or sufficient to document such an interaction. We outline the evidence which we believe must be sought: it must be established that collectors are particle-limited, that shredder activity produces particles, that shredder activity enhances collector performance, and that the mechanism for this enhancement lies in particle production and not some other process. We review available data that bear on these propositions, and describe a straightforward experiment which could unambiguously test the shredder-collector facilitation hypothesis