Showing papers by "James H. Cane published in 1993"

Regional, annual and seasonal variation in pollinator guilds: intrinsic traits of bees (Hymenoptera: Apoidea) underlie their patterns of abundance at Vaccinium ashei (Ericaceae)

Abstract: We studied the numerical importance of bees as pollinators of rabbiteye blueberry, Vaccinium ashei Reade, in the southeastern United States. Most of the 27 bee species were rare at V. ashei flowers. Three taxa of bees were often abundant at V. ashei : the honey bee, Apis mellifera L.; queens of four bumble bee species ( Bombus spp.); and the southeastern blueberry bee, Habropoda laboriosa (F.). Most bee species that co-occur with cultivated V. ashei do not visit its flowers either because adults emerge late in the spring following bloom, or their tongues are too short to probe the flowers effectively. The more common bees varied in their regional, annual, and seasonal abundances at cultivated V. ashei , reflecting inherent differences in sociality, foraging predilections, voltinism, and adult phenologies. Our censuses showed that H. laboriosa is a Vaccinium specialist (2 yr, two states, four habitats). Compared with the other common bees, abundance of H. laboriosa at V. ashei was most variable regionally, least variable annually, and most predictable daily during a flowering season. For 6 yr, adult activity of Bombus queens and univoltine H. laboriosa generally spanned the season of V. ashei flowering. Spatial patchiness but local reliability of H. laboriosa may be an outcome of its oligolectic floral preferences. In contrast, polylectic honey and bumble bees were regionally ubiquitous. However, the temporal abundance of honey bees fluctuated markedly at V. ashei , perhaps reflecting their shifting preferences among competing members of a local flora.

Temporal patterns of floral visitation for two bee species foraging on Solanum

Abstract: Timing of floral visits was recorded for two bee species, Ptiloglossa arizonensis and Bombus sonorus, on the nightshade Solanum elaeagnifolium at a site in southeastern Arizona. Periodic censuses revealed that P. arizonensis foraged between 0500-0600 hours, whereas workers of B. sonorus were most common after 0700 hours. Continuous obser vations of focal flowers revealed the same pattern, as P. arizonensis accounted for nearly 100% of the initial three visits to the focal flowers. These observations also revealed that floral visits often did not involve pollen collection but were simply investigatory in nature. For both species, we examined whether investigatory visits were more likely to occur at flowers that had received a high number of prior visits. Buchmann and Cane (1989) recently investigated the foraging behavior of two bee species, Ptiloglossa arizonensis Timberlake and Bombus sonorus Say, on the nightshade Solanum elaeagnifolium Linnaeus. As in other Solanum species, flow ers of S. elaeagnifolium lack nectaries and offer only pollen as a reward for floral visitors. In addition, the pollen is released through minute pores and can be efficiently collected only via sonication of the anthers (Linsley and Cazier, 1970). Through experimental manipulation of pollen accessibility, Buchmann and Cane (1989) made two major findings regarding the foraging behavior of the bees. First, individuals of both P. arizonensis and B. sonorus assess pollen harvest from single flowers and modify their foraging behavior accordingly. For both species, floral handling times were longer for control, virgin flowers than for experimental flowers that (following manipulation) afforded no pollen. Second, individual P. arizonensis spent less time handling virgin flowers but appeared to collect more pollen per flower (based on grooming frequency) than individual B. sonorus. This finding indicates a trade-off between dietary specialization and foraging efficiency, as the solitary P. arizonensis is a "sonication oligophage" (Buchmann and Cane, 1989), whereas the social B. sonorus is a polylectic generalist (Shelly et al., 1991). This latter finding suggests that, in terms of floral use, P. arizonensis may have a competitive advantage over B. sonorus in exploiting S. elaeagnifolium as a pollen source. In addition, P. arizonensis is a matinal bee, active just before and after sunrise (Linsley, 1962), whereas B. sonorus is not fully active until 1-2 hr after sunrise (Shelly et al., 1991). Consequently, P. arizonensis typically visits S. elaeagnifolium flowers before B. sonorus (Linsley and Cazier, 1970). Based in the same locality, the present study more closely examines this inter specific difference in the timing of floral visits. Specifically, we describe temporal variation, not only in the overall abundance of foraging bees, but also in the 1 Hawaiian Evolutionary Biology Program, University of Hawaii, Honolulu, Hawaii 96822. 2 Department of Biology, University of California, Los Angeles, California 90024. 3 USDA, ARS, Carl Hayden Bee Research Center, 2000 E. Allen Road, and Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, Arizona 85719. 4 Department of Entomology, Auburn University, Auburn, Alabama 36849. Accepted for publication 5 April 1993. This content downloaded from 157.55.39.4 on Sat, 10 Sep 2016 05:29:24 UTC All use subject to http://about.jstor.org/terms 320 JOURNAL OF THE KANSAS ENTOMOLOGICAL SOCIETY number of bee visits to individual flowers. These latter data give perhaps a more accurate description of the temporal advantage enjoyed by P. arizonensis, since they allow estimates, on a per flower basis, of the number of P. arizonensis visits that occur prior to the arrival of B. sonorus. In addition, we observed that, particularly for B. sonorus, floral visits often did not involve pollen collection but were simply "investigatory" in nature. Correspondingly, we examined whether these investigatory visits were more likely to occur at flowers that had received more frequent prior visits. Materials and Methods Field work was conducted between August 17-24, 1985, 2 km north of Portal, Cochise Co., Arizona, along the Foothills Hwy. On these days, skies were in variably clear during our observations. All observations were made in a single patch of S. elaeagnifolium (approximately 400 m2 in area) growing next to a cattle stocktank. Vegetation in the surrounding area consisted of Chihuahuan desert scrub dominated by creosote bush {Larrea tridentata). Censuses of foraging bees were made at 10 min intervals between 0500-0730 hours on five different mornings. During each census, observers counted all P. arizonensis and B. sonorus found within five plots of 1 m2. Prior to each census, ambient temperature 1 m above ground was measured to the nearest 1?C using a Bailey Bat-12 thermocouple thermometer. Relative light intensity was also recorded with a Gossen Scout-2 light meter (held vertically). These readings were later converted to Lux by calibrating the Gossen Scout-2 model against a Gossen Lunasix light meter. We also monitored visits to individual flowers of S. elaeagnifolium. Continuous observations were made of 15 flowers between 0500-0730 hours on four different mornings (a different set of flowers was observed each day). Focal flowers were selected one day prior to observations when they appeared as large purple buds. At that time a small piece of masking tape bearing an identification number was placed on the stem well below the flower. To ease observations, all flowers ob served on a given day were situated within a 3-4 m2 area. To avoid any positional bias, observations of focal flowers were made in different parts of the patch on different days. While monitoring individual flowers, we noted the number of visits by each species during 10 min intervals throughout the morning. Since the bees were not marked, counts may have included repeat visits by some individuals. We also noted whether the visits involved pollen collection (via sonication) or were simply investigatory in nature. During the latter, bees hovered immediately in front of a flower for 1-3 sec and then flew away without alighting on or even contacting the flower. Finally, on two mornings, we made continuous observations of in dividual bees and recorded the number of floral visits made. Focal bees were observed for 1-5 min. Fig. 1. (a) Censuses of foraging bees at the study patch of S. elaeagnifolium. Values represent means for five 1 m2 plots monitored over five mornings (i.e., n = 25 for each point). Vertical bars give ? 1 SD. Plots were checked every 10 min. Measurements of (b) ambient temperature and (c) light levels during hours of field observations. Values represent means over five mornings; vertical bars give ? 1 SD. This content downloaded from 157.55.39.4 on Sat, 10 Sep 2016 05:29:24 UTC All use subject to http://about.jstor.org/terms VOLUME 66, NUMBER 3 321