TROPHIC ECOLOGY OF 5 SHREDDERS IN A ROCKY-MOUNTAIN STREAM

The trophic ecology of five shredder taxa found in Mink Creek, Idaho was determined in laboratory food quality experiments to assess the obligate or facultative nature of resource utilization among lotic taxa commonly referred to as detritivores. The experiments tested resource assimilation for each taxon among three major resources available to primary consumers in streams; periphyton, fine particulate detrital material (FPM) and coarse particulate detrital material (CPM). Growth of each taxon was determined on each resource in laboratory experiments conducted at 10 degrees C. Growth results indicate that only one of the five taxa (middle-late instar Dicosmoecus atripes) was an obligate CPM detritivore. The remaining four taxa (Amphinemura banksi, Lepidostoma sp., Podmosta delicatula, and Zapada cinctipes) were generalists capable of growth on at least two of the three resource types. Ail four generalists exhibited growth on periphyton and CPM resources suggesting that these taxa can utilize both autochthonous and allochthonous resources. Our results do not support the idea that taxa with similar mouthpart morphology, specifically shredders, exhibit similar trophic relationships.