TROPHIC ECOLOGY OF 5 SHREDDERS IN A ROCKY-MOUNTAIN STREAM

The trophic ecology of five shredder taxa found in Mink Creek, Idaho w as determined in laboratory food quality experiments to assess the obl igate or facultative nature of resource utilization among lotic taxa c ommonly referred to as detritivores. The experiments tested resource a ssimilation for each taxon among three major resources available to pr imary consumers in streams; periphyton, fine particulate detrital mate rial (FPM) and coarse particulate detrital material (CPM). Growth of e ach taxon was determined on each resource in laboratory experiments co nducted 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 capa ble of growth on at least two of the three resource types. Ail four ge neralists exhibited growth on periphyton and CPM resources suggesting that these taxa can utilize both autochthonous and allochthonous resou rces. Our results do not support the idea that taxa with similar mouth part morphology, specifically shredders, exhibit similar trophic relat ionships.