MOVEMENT PATTERNS AND ECOLOGY OF PTERONARCYS NYMPHS (PLECOPTERA) - OBSERVATIONS OF MARKED INDIVIDUALS IN A ROCKY-MOUNTAIN STREAM

1. Individually tagged Pteronarcys californica (Newport) nymphs were caught and recaptured over a 3-month period to determine their movement patterns and home range size. Sex/age structure, population density, and food habits (from gut contents) were also recorded. More than 1000 nymphs were tagged of which 256 (25%) were recaptured at least once. Tagged insects were confined to contiguous fast water, cobble riffles. Low velocity, silt-bottomed pools acted as barriers. 2. This stonefly has a 3-year life cycle although only the two oldest nymphal size-classes were tagged. Females were larger than males at all ages. The population sex ratio was skewed 60:40 towards females. Densities averaged 1.7 m-2 +/- 0.17 SE (range 0-19 m-2). 3. Most movements were short, indicating that a majority of the stoneflies stayed within a few metres of their first capture point (mean 1.8 m downstream +/- 0.51 SE, range 44 m downstream to 40 m upstream). Significant patch size is a stream reach 24 m long that would contain 85% of the average individual's movements. Time between captures averaged 16 d +/- 0.734 SE (maximum 81 d). Eight individuals were notable for extremely rapid upstream movements ranging from 6 to 22 m d-1. 4. Frequency of movements up and downstream differed significantly between the sexes. Pteronarcys distribution was clumped with certain quadrats representing 'zones of attraction.' The stoneflies moved rapidly between zones, then stayed many days in those areas. Movements differed significantly from random walk models. 5. Guts contained 75% diatoms, 15% vascular plant material, and 8% animal remains. Females ate significantly more diatoms than males on a volumetric basis.