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Grand Teton National Park Report

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Controversy continues over the relative importance of resource limitation and intraspecific competition in stream ecosystems (Grossman et al 1982, Hart 1983). The chief trouble is separating density independent effects (e.g., Knight and Gaufin 1963) from effects that are density-dependent (i.e., biological) (Peckarsky 1979). Movements of marked individuals can reveal fine detail about intraspecific coupetition or effects of environmental heterogeneity. My research uses individually marked stoneflies (Pteronarcys californica) to study movement patterns. Pteronarcys was chosen because it is large enough to tag and can be caught by electroshocking. The work has 2 parts: a descriptive study of stonefly novements, and a series of manipulations to probe factors affecting them. The descriptive study was conducted in 1987: (1) to determine feasibility of catching and marking large numbers of stoneflies; (2) to obtain life history data (sex, size, phenology); (3) to find out the size of Pteronarcys home ranges; and (4) to discover maximum distance and maximum rate the stoneflies can move. Purposes (3) and (4) were intended to guide formulation of the manipulation study by providing an estimate for sample and quadrat sizes. The manipulation study, (July-November 1988), was a randomized block ANOVA design. Food and stonefly density were manipulated in 4m2 quadrats in Pacific Creek. Purposes of the manipulation were: (1) to see if stoneflies use available habitat differentially; (2) to discover the relative importance of food availability in explaining stonefly distribution; (3) to test for intraspecific interactions as determinants of movement; (4) to look for interactions between food and intraspecific factors. I present here some results from 1987 and summarize data from 1988 (only now beginning to be analyzed).