. The Canadian field-naturalist. 520 The Canadian Field-Naturalist Vol. 104 hypotheses: (1) that bumblebee foraging is random with respect to direction; (2) that bumblebees tend to forage between closest plants; and (3) that bumblebees avoid recently visited plants. Results herein are discussed with reference to optimal foraging theory (Michener 1974; Pyke et al. 1977; Pyke 1978), and plant morphology and distribu- tion (Larson and Larson 1987). Materials and Methods A patch of Spiranthes romanzoffiana with bumblebee foragers (mostly Bombus bifarius and a few Bombus terricola occidentalis work
. The Canadian field-naturalist. 520 The Canadian Field-Naturalist Vol. 104 hypotheses: (1) that bumblebee foraging is random with respect to direction; (2) that bumblebees tend to forage between closest plants; and (3) that bumblebees avoid recently visited plants. Results herein are discussed with reference to optimal foraging theory (Michener 1974; Pyke et al. 1977; Pyke 1978), and plant morphology and distribu- tion (Larson and Larson 1987). Materials and Methods A patch of Spiranthes romanzoffiana with bumblebee foragers (mostly Bombus bifarius and a few Bombus terricola occidentalis workers) was located at Spectacle Lake Provincial Park (° N, ° W) on southern Vancouver Island, British Columbia, Canada. The patch comprised twelve S. romanzoffiana plants situated within a 5 X 12 m area on an exposed hilltop (elevation approx. 300 m). The moss and grass- covered site was surrounded by scattered Lodgepole Pine and Douglas Fir. The 12 plants (assigned numbers and mapped) were sparsely distributed (mean = plants m"^) and irregularly arranged (distance between adjacent plants ranging from m) (Figure 1). Measured to the nearest 1 cm, orchid spikes ranged in height from 12-27 cm; inflorescence lengths (portion of the spike covered by flowers) ranged from 3-6 cm. The pollination state of the flowers was assessed by noting their color and shape: unpollinated flowers were white and open (2-15 per inflorescence) and emitted a shght, musty-sweet fragrance; pollinated flowers were brown and closed (0-8 per inflorescence) and were situated below the unpollinated flowers (Figure 2). Observations of foraging insects were made on 16 August 1983 (1300-1600; 1630-1900 hrs PDT). Figure 1. Locations of the \1 Spiranthes romanzoffiana plants (plant number at circle) within the 5 X 12 m study area. Lines between circles indicate the main flight path. 16-1 12 8- i open closed 1 a G 4 5 6 7 8 9 10 11 12 Plant Number Figure 2. Histogram showing number of ope
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