Behavior of queen bumblebee pollinators on Primula sieboldii (Primulaceae) in response to different patch sizes and spacing



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      Present address: Environmental Biology Division, National Institute for Environmental Studies, 16-2 Onogawa, Tsukuba, Ibaraki 305-8506, Japan.


    1. Graduate School of Agricultural and Life Sciences, The University of Tokyo, Bunkyo, Tokyo 113-8657, Japan
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Fumiko Ishihama


Pollinator visitation patterns are strongly affected by the spatial structure of a plant population. We assessed the effects of the size and spacing of patches on the foraging behavior of queens of Bombus diversus tersatus on a heterostylous perennial species, Primula sieboldii, using an experimental population. We compared Akaike's information criterion (AIC) among candidate statistical models, and models with patch size had the lowest AIC in various aspects of visitation behavior. Visitation frequency per patch increased with increasing patch size, but the proportion of visited flowers decreased. As a result of this combination of visitation patterns, visitation frequency per flower was only slightly affected by patch size. This result indicates that the bumblebees came close to an ideal free distribution for the use of resources in terms of the patch size within a population. From the plant's point of view, increasing the number, but decreasing the proportion, of flowers visited in larger patches would maximize reproductive success by minimizing inbreeding. Although patch size strongly affected visitation frequencies, patch spacing had a moderate effect only on the visitation frequency per patch. Visitation frequency per patch was higher with closer spacing between patches. No evidence for an interaction between patch size and spacing was detected.