1. The relative extent of generalist or specialist resource use strategies is an important question in ecology. A community dominated by specialist strategies suggests a high level of interspecific competition for resources, resulting in the evolutionary development of isolating mechanisms between species (e.g. resource specialization to avoid and/or outcompete other species). A community dominated by generalist strategies suggests less interspecific competition for resources, allowing many taxa to utilize the same resources. In stream systems, generalist food habits are a common strategy among primary consumers, but little is known about resource assimilation strategies (resources incorporated into tissue growth). Published data indicate that generalist resource assimilation strategies may prevail in lotic systems as well. 2. Functional feeding groups (FFGs) are often used to infer resource assimilation among lotic macroinvertebrates (e.g. shredder‐detritivore, scraper‐herbivore). While these groupings are aptly used to describe invertebrate feeding modes and community structure, the use of FFGs to describe resource assimilation among lotic consumers is not appropriate. Sufficient data now exist to seriously question how accurately FFG assignments describe the processes of energy flow and material transfer between trophic levels in stream ecosystems. 3. Because FFGs may not accurately describe functional attributes in lotic systems, an alternative approach is needed. One approach is to determine the amount of secondary production that is derived from autochthonous (e.g. periphyton and algae) and allochthonous (e.g. detritus) resources directly. A simple model of community function based on this approach is presented. The model incorporates trophic generalists into measurement of consumer–resource energetics in lotic systems.

The trophic ecology of 11 benthic macroinvertebrate taxa found in Cache Creek, Yellowstone National Park (YNP) was studied to determine if burned organic matter is an important resource and how resource utilization patterns may be altered in post—fire streams. Laboratory food quality experiments were conducted to determine the growth response of each species when grown on several resource types: burned organic matter, periphyton, unburned coarse particulate material (CPM), and unburned fine particulate material (FPM). The central hypothesis of this research was that benthic macroinvertebrates cannot use burned organic matter as a resource. A secondary hypothesis was that some benthic macroinvertebrates are facultative in trophic function, with the ability to use both allochthonous and autochthonous resources for growth. Of the 11 taxa studied, only one (Paraleptophlebia heteronea) could grow on burned organic matter as a resource, indicating that post—fire food webs probably do not exhibit major shifts in resource utilization to burned material. Two species were generalist detrivores (P. heteronea, Ameletus cooki) able to use both natural FPM and CPM resources. Two species were specialist detritivores (Oligophlebodes sigma, Ephemerella infrequens) growing only on unburned CPM resources, and two (Cinygmula mimus, Epeorus albertae) were specialist herbivores utilizing only periphyton. Five species were generalist herbivore—detritivores (Baetis bicaudatus, Drunella doddsi, D. coloradensis, D. spinifera, Zapada columbiana), exhibiting growth on both detritus and periphyton resources. Based on the experimental results, trophic generalists are common food web components in Yellowstone streams. Two of the most abundant benthic macroinvertebrates during post—fire recovery, B. bicaudatus and Z. columbiana, were trophic generalists, indicating that some generalists may be disturbance adapted. In this study, published functional feeding group classification did not indicate obligate resource utilization (growth on only one resource type) for most taxa studied. Comparison of a food web for Cache Creek based on functional feeding group classification and one based on the results of this study indicates that the inclusion of generalists in the web results in a more realistic approximation of food web relationships such as the link—species scaling law. Our results suggest that future research should include spatial and temporal aspects of resource switching and generalist resource utilization by individual lotic primary consumers.

Wildfi re disturbance can alter stream ecosystems in numerous ways including loss of riparian litter inputs, altered fl ow regimes, shifts in resource allocations, and changes in biotic community structure. While some information exists on long-term recovery of streams following wildfi re, patterns in trophic dynamics are poorly understood. This study involved comparison of trophic pathways in reference and post-fi re streams in Yellowstone National Park (YNP) in 1998, ten years after wildfi re. 2 nd and 3 rd order post-fi re catchments in Cache Creek, YNP showed an increase in autochthonous grazing pathways compared to reference streams. The shift from detrital to grazing pathways, however, was less pronounced in 1998 (10-yrs post-fi re) than it was in 1990 (2-yrs post-fi re). Post-fi re stream energy pathways showed an initial shift to autochthonous resources followed by recovery toward pre-fi re allochthonous pathways over the fi rst post-fi re decade. Increasing energy derived from allochthonous resource pathways is expected to continue until it reaches pre-fi re conditions in Yellowstone streams.