Floral abundance and bee density affect species-specific foraging patterns of alpine bumble bees
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ORIGINAL PAPER
Floral abundance and bee density affect species‑specific foraging patterns of alpine bumble bees Akari Shibata1 · Gaku Kudo1 Received: 3 December 2019 / Accepted: 10 October 2020 © Springer Nature B.V. 2020
Abstract In response to the qualitative and quantitative changes in floral resources, bumble bees flexibly forage multiple plant species throughout the growing season. During the short summer in an alpine ecosystem, the activity of worker bees is maximized in the middle of the season, when the competition for floral resources may be intense. We predicted that the foraging patterns of bumble bees are affected by both relative floral abundance and interactions between bumble bee species. We recorded the floral abundance of individual plant species and the foraging frequency of bumble bees in an alpine meadow during the major flowering period over 3 years. Two bumble bee species were common during the major flowering period. Although they tended to visit abundant floral species, the shorter-tongued species (Bombus hypocrita) showed a more diverse and flexible floral choice than the longer-tongued species (Bombus beaticola). The degree of floral use overlap between two bumble bee species tended to decrease when the foraging density of the longer-tongued species was high. These results indicated that multiple bumble bee species are able to coexist when certain bee species can flexibly change targeting flowers in response to the temporal variations in flowering species and the density of competing bee species. The extent of foraging flexibility is related to the morphological traits of bee species and availability of floral resources. Keywords Bombus · Floral choice · Flowering phenology · Pollination · Seasonal dynamics · Visitation frequency
Introduction Bumble bees (Bombus spp.) are the most common and effective pollinators in cool-temperate, alpine, and subarctic ecosystems (Heinrich 1979; Bingham and Orthner 1998; Kudo 2016). They are eusocial insects with an annual life cycle, and their colony growth and reproductive success depend on the availability of floral resources (Schmid-Hempel and Schmid-Hempel 1998; Pelletier and McNeil 2003; Inari et al. 2012). Reflecting the annual cycle of colony development, the activity of worker bees is maximized in the middle of summer. In the short growing season of alpine environments, Handling Editor: Heikki Hokkanen. Electronic supplementary material The online version of this article (https://doi.org/10.1007/s11829-020-09787-0) contains supplementary material, which is available to authorized users. * Akari Shibata [email protected] 1
Faculty of Environmental Earth Science, Hokkaido University, Sapporo, Hokkaido 060‑0810, Japan
floral visits by worker bees drastically increase after midJuly (Kudo 2016). Intensive floral use by worker bees may cause the partitioning of floral resources among bee species, but the pattern of interspecific resource partitioning was not consistent in the previous studies (Goulson 2010; MillerStruttmann and Galen
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