. The Canadian field-naturalist. 192 The Canadian Field-Naturalist Vol. 114 1995. Date 2nd Instar -^y- 3rd Instar 4th Instar - - 5th Instar Figure 3. Percent of sampled Dicosmoecus gilvipes 2nd, 3rd, 4th, and 5th instars on each sample date in 1995, 1996, and 1997 in Quartzville Creek, Oregon. selecting bedrock as foraging areas; this preference may have been based on a variety of physical charac- teristics or local prey abundance. At the site scale, harlequin distribution did not appear to be determined by food availability; they were not significantly relat- ed to densities of D. gilvipes, t
. The Canadian field-naturalist. 192 The Canadian Field-Naturalist Vol. 114 1995. Date 2nd Instar -^y- 3rd Instar 4th Instar - - 5th Instar Figure 3. Percent of sampled Dicosmoecus gilvipes 2nd, 3rd, 4th, and 5th instars on each sample date in 1995, 1996, and 1997 in Quartzville Creek, Oregon. selecting bedrock as foraging areas; this preference may have been based on a variety of physical charac- teristics or local prey abundance. At the site scale, harlequin distribution did not appear to be determined by food availability; they were not significantly relat- ed to densities of D. gilvipes, total benthics, or EPT taxa. Therefore, it appeared that harlequins in Quartzville Creek selected foraging areas based on stream hydrology and substrate characteristics. Ducks may prefer bedrock because of: (1) relatively laminar flow increasing visibility, (2) light coloration provid- ing a contrast to detect prey, particularly cases of D. gilvipes, (3) absence of finer particulates resulting in more efficient feeding, and (4) lack of substrate com- plexity reducing invertebrate refuges. Dicosmoecus gilvipes may prefer bedrock because algae are readily accessible and abundant in open-canopied systems (Tait et al. 1994). In addition, swift laminar flow. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Ottawa Field-Naturalists' Club. Ottawa, Ottawa Field-Naturalists' Club
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