|Abstract or Summary
- The purpose of the study was to provide quantitative information on the utilization and processing of leaves and needles by several species of caddisfly larvae.
Field and laboratory studies were conducted on three species of Lepidostoma Rambur (Lepidostomatidae), from Willamette Valley and Cascade Mountain streams, and on Clistoronia magnifica (Banks) (Limnephilidae) from a Cascade lake. These species were selected to represent a wide range of habitats, food sources, and developmental patterms.
Consumption, fecal production, growth, and assimilation efficiency were measured gravimetrically in the laboratory as influenced by food quality (food type and conditioning time), food quantity, larval size, and temperature. Respiration was measured with a Gilson respirometer as influenced by temperature and larval size. Consumption rates generally increased with temperature and conditioning of the food, and decreased with increased larval size. Mean assimilation efficiencies were 20 to 30% for L. quercina Ross and Douglas fir needles, and 57% for C. magnifica fed on wheat grains. Assimilation efficiency of alder leaves by L. quercina decreased with higher temperatures, while assimilation efficiency of alder by C. magnifica increased with temperature. This may reflect physiological adaptations to the species' respective temperature regimes. Maximum consumption rates by L. quercina were reached when food (alder) was only slightly in excess, in contrast to consumption rates by L. unicolor (Banks) which did not reach maximum until food (Douglas fir) was greatly in excess. Net growth efficiency of L. unicolor fed on Douglas fir needles (60%) was higher than for L. quercina fed on alder leaves (13%) or C. magnifica fed on alder plus wheat (33%). Increased food selectivity and high net growth efficiency are apparently adaptations by L. unicolor for utilizing poorly digestible food.
Respiration rates were highest for smaller larvae. Temperature effects on respiration rates were largest for those species found in habitats with little temperature variation (e.g. Q₁₀ for L. unicolor was 1.99). C. magnifica larvae, normally experiencing a temperature range from 4 to 25°C, showed a respiratory Q₁₀ of 1.12, indicating almost complete compensation for changes in temperature. The ability to compensate for changes in temperature appeared to be most pronounced in the larval sizes most often exposed to temperature fluctuations (e.g. first- through fourth-instar L. quercina or late-final instar L. unicolor).
In the field, L. cascadense and L. unicolor appeared to minimize competition for food, occurring in different microhabitats and growing most rapidly at different times of the year. Estimated annual production for the three species of Lepidostoma was nearly identical (0.23 to 0.26 gm⁻²), requiring approximately 3 gm⁻² of deciduous leaves for L. quercina and 9 to 10 gm⁻² of conifer needles each for L. cascadense and L. unicolor. Production of fine particulate material was thought to be the species' most important impact on the stream system and could support collector production of up to 5 gm⁻². Simulation modeling of L. quercina growth, based on laboratory data on feeding and respiration, suggested that food quality may be limiting factor for growth in the field.
It was concluded that the species studies exhibited a wide variety of adaptive strategies for using allochthonous foods in their respective habitats and these strategies result in maximum utilization of food when it is most available and usable. Identification and characterization of different strategy-types could be valuable in understanding stream systems and predicting their behavior.