The conversion of allochthonous material by stream detritivores Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/n583xz159

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  • The role of detritivores in the conversion of allochthonous leaf material in two small streams in the Cascade Range of Oregon was studied. Their importance in relation to other consumers was estimated from emergence and benthic standing crop data. Ingestion rates and efficiencies of utilization of bigleaf maple (Acer macrophyllum) and red alder (Alnus rubra) leaves by several species of stream detritivores, one species of stonefly and several species of caddis lies, were measured under field or laboratory conditions. Mean consumption rates varied from 0. 04 mg/mg/day for Halesochila taylori larvae (Trichoptera:Limnephilidae) feeding on maple leaves to 0.60 mg /mg /day' for Lepidostoma sp. larvae (Trichoptera :Lepidostomatidae) feeding on alder and maple leaves. Ecclisomyia sp. larvae (Trichoptera:Limnephilidae) consumed 0.10 mg/mg/day of maple leaves in the field. All consumption rates were calculated assuming constant feeding rates by the insects and constant rates of leaf decomposition without insects, but a model is discussed that allows non-linear feeding and leaf decomposition rates. Efficiency of food utilization was measured either as assimilation efficiency, the ratio of assimilated food (ingestion minus egestion) to consumption; or as gross growth efficiency, the slope of the growth:consumption line calculated by linear regression analysis. Assimilation efficiencies ranged from 7.4% for Heteroplectron californicum larvae (Trichoptera:Calamoceratidae) fed on maple leaves to 12% for Lepidostoma sp. larvae fed on alder and maple leaves. In order to assess the role of microbial communities in leaf utilization by Pteronarcys princeps (Plecoptera:Pteronarcidae), nymphs were fed untreated maple leaves and maple leaves treated to reduce bacterial or fungal populations, for a period of 54 days. Gross growth efficiency when fed on untreated leaves was 4.94% compared with 1.03% for the insects fed antibacterial treated leaves. When fed fungicide treated leaves, the mean consumption rate was less than 10% of the consumption of untreated leaves and mortality was 85% compared with 15% for the insects fed untreated leaves. It was concluded that bacteria play a major role in the utilization of leaves by Pteronarcys princeps and that fungi are important as astimulus to feeding, although they may also aid in utilization of the leaves. To aid in classifying the emergence and benthos data into trophic categories, an extensive literature review of the foods of aquatic insects was compiled. The estimated yearly emergence of aquatic insects from Watershed 10 was 81 mg/m² /yr. of algivores, 253 mg/m²/yr. of detritivores, and 135 mg/m²/yr. of carnivores. The mean standing crop of aquatic insects in an old-growth location in Mack Creek was 0.85 g/m² of algivores, 3.10 g/m² of detritivores, and 2.31 g/m² of carnivores; and 0.83 g/m² of algivores, 1.57 g/m² of detritivores, and 4.04 g/m² of carnivores in a clear-cut location. A model is included describing the cycling of energy within the detrital component of the stream system, reflecting the importance of the fecal material and leaf fragments that return to the detrital pool.
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