Santa Cruz Island Reserve

29 Jun, 05 AM - 01 Jul, 05 AM

(This is the description of the project as it appears in the NGS proposal.) Project Title: Measuring the Recovery of an Island Ecosystem after Removal of Honey Bees Principal Investigator: John F. Barthell Co-investigators: John M. Randall, Robbin W. Thorp and Adrian M. Wenner Objective: This study will duplicate an experiment we conducted nine years ago in order to assess the aftereffect of feral honey bee removal from an island ecosystem. We will monitor plant visitors and determine seed set as measures of our ability to restore a native pollinator community on Santa Cruz Island (California, USA). INTRODUCTION Background. In 1993 the participants in this proposal conducted an experimental exclusion study (see methods below) at three locales in California to assess the impact of honey bees on seed production in the highly invasive yellow star-thistle, Centaurea solstitialis L. (Barthell et al. 2001). The varroa mite, Varroa destructor Anderson and Trueman, was just becoming established in California at that time and was introduced to one of our sites, Santa Cruz Island, immediately after that study. Without a commercial source of honey bees entering the island since then (due to its protected status), we witnessed a striking decline in honey bee colonies on the island as a result of this parasite?s activities (Wenner et al. 2000). This fact provides us with an opportunity to assess the response of yellow star-thistle to widespread removal of honey bees on the island. The demonstration that honey bees promote seed set in weeds is important for at least two reasons. First, it contributes to a recently rekindled debate about the effect of introduced honey bees on the native plant and pollinator communities they have invaded throughout the world. At least one review suggests that honey bees do not significantly impact native systems (Butz Huryn 1997). Studies do show that high densities of honey bees at flower patches (real and artificial) depress native bee species numbers (Roubik 1978 and 1980, Schaffer et al. 1979 and 1983), but lack direct evidence that the reproduction of native bees is compromised in the process (e.g., Roubik 1983). Honey bee impact on non-native plants like yellow star-thistle is less studied, but the results of our study (Barthell et al. 2001) contrast with the conclusion of the review described above (Butz Huryn 1997, also see Butz Huryn and Moller 1995). We are interested in exploring this particular issue among the Channel Islands where introduced plant species represent high proportions of the respective floras (Junak et al. 1995). A second implication of our work is that honey bees and weeds may act as invasive mutualists that assist one another?s tendency to succeed in new environments. In other studies we demonstrated that honey bees show preference for yellow star-thistle over native counterparts, including gumplant or Grindelia camporum E. Greene (Thorp et al. 1994 and 2000). In a later experimental study, honey bees were found to promote seed set in yellow star-thistle but not in nearby gumplants (Barthell et al. 2000). Collectively, our results now suggest that honey bees may be seeking old associations (through mutualism) with plants from their area of origin: Eurasia. If this is found to be a widespread phenomenon, it suggests that mutualisms may be an important factor in determining native plant community resistance to exotic invaders (Richardson et al. 2000). With the severe decline in honey bees on Santa Cruz Island, we now have an opportunity to measure an effect of restoring the native Santa Cruz Island pollinator community. MATERIALS AND METHODS Flower Visitation. Thirty study plants (separated by about 1 m) would be selected along each of three transects on Santa Cruz Island. The eastern-most of these is located near a chapel between Prisoner?s Stream and the main ranch settlement on the island. The second transect is located west of a field station operated by the University of California while the western-most transect is at the western end of the Central Valley (near a spring known as Cascada). Study plants at all three transects will be simultaneously monitored for visitors during each of four 30-min time periods beginning at 09:00, 12:00, 15:00 and 18:00. At the beginning of each of these periods, an observer walks for 2.5 min along each transect, recording the number and types of visitors on the 30 study plants. This process will be repeated (back and forth) for 30 min. Seed Production. The same 30 plants from each transect used in the flower visitation monitoring study will be used to examine seed set (reproductive) effects. The crown of each plant will be divided into four quadrants. Treatments will then be randomly applied to a designated flower bud in each quadrant. The treatment exclosures will be constructed of nylon mesh cut into 20 cm-diameter circles and equipped with draw-strings. Each treatment is characterized below. Small Mesh: A one mm diameter mesh that prevents all bee visitors from contacting the flower head and is an indicator of the plant?s ability to self-pollinate. Medium Mesh: A three mm diameter mesh will exclude large-bodied anthophorids, bumble bees and honey bees while allowing the passage of small- to medium-bodied bees (including all species of Halictidae). This mesh diameter would also allow entry by species of Megachilidae (e.g., mason and leafcutting bees). Our past work demonstrates this to be the most critical treatment for comparison with the control since it excludes honey bees but allows all common native bees known on Santa Cruz Island to enter the bag. Large Mesh: A five mm diameter mesh bag is designed to exclude large-bodied anthophorid bees and bumble bees, while allowing honey bees and other small- to medium-bodied bees such as halictid bees to enter the treatment bag. Control: No mesh bagging will be applied, allowing all visitors access to flower heads. All treated flower heads will be allowed to fully develop and begin senescence before being wrapped in a very fine mesh material that will prevent any seed dispersal. When the seed heads completely dry, they will be removed from the plants and grouped into plastic bags according to plant, replicate and treatment. Seeds dissected in the lab from heads will be grouped as ?viable? and ?non-viable?, including those from both disc (in the flower head center) and ray (at the flower head periphery) flower types. Percent seed set will be calculated by dividing the number of viable seeds by the total number of seeds (viable and non-viable) contained in each head. As before, we will analyze percent seed set differences among treatments. These results will be compared with published seed set measurements taken prior to the decline of honey bees on Santa Cruz Island. LITERATURE CITED Barthell, J. F., J. M. Randall, R. W. Thorp and A. M. Wenner. 2001. Promotion of seed set in yellow star-thistle by honey bees: evidence of an invasive mutualism. Ecological Applications 11:1870-1883. Barthell, J. F., R. W. Thorp, A. M. Wenner and J. M. Randall. 2000. Yellow star-thistle, gumplant, and feral honey bees on Santa Cruz Island: a case of invaders assisting invaders. Pages 269-273 in D. R. Browne, K. L. Mitchell and H. W. Chaney, editors. Fifth California islands symposium. MBC Applied Environmental Sciences, Costa Mesa, California, USA. Butz Huryn, V. M. 1997. Ecological impacts of introduced honey bees. Quarterly Review of Biology 72:275-297. Butz Huryn, V. M., and H. Moller. 1995. An assessment of the contribution of honey bees (Apis mellifera) to weed reproduction in New Zealand protected natural areas. New Zealand Journal of Ecology 19:111-122. Junak, S. T., T. Ayers, R. Scott, D. Wilken and D. Young. 1995. A flora of Santa Cruz Island. Santa Barbara Botanical Garden, Santa Barbara, California, USA. Richardson, D. M., N. Allsopp, C. M. D?Antonio, S. J. Milton and M. Rejm?nek. 2000. Plant invasions -- the role of mutualisms. Biological Review 75:65-93. Roubik, D. W. 1978. Competitive interactions between neotropical pollinators and Africanized honey bees. Science 201:1030-1032. Roubik, D. W. 1980. Foraging behavior of competing Africanized honeybees and stingless bees. Ecology 61:863-845. Roubik, D. W. 1983. Experimental community studies: time-series tests of competition between African and neotropical bees. Ecology 64:971-978. Schaffer, W. M., D. B. Jensen, D. E. Hobbs, J. Gurevitch, J. R. Todd and M. Valentine Schaffer. 1979. Competition, foraging energetics, and the cost of sociality in three species of bees. Ecology 60:976-987. Schaffer, W. M., D. W. Zeh, S. L. Buchmann, S. Kleinhans, M. Valentine Schaffer and J. Antrim. 1983. Competition for nectar between introduced honey bees and native North American bees and ants. Ecology 64:564-577. Thorp, R. W., A. M. Wenner and J. F. Barthell. 1994. Flowers visited by honey bees and native bees on Santa Cruz Island. Pages 259-286 in W. L. Halverson and G. J. Maender, editors. Fourth California islands symposium: update on resources. Santa Barbara Museum of Natural History, Santa Barbara, California, USA. Thorp, R. W., A. M. Wenner and J. F. Barthell. 2000. Pollen and nectar resource overlap among bees on Santa Cruz Island. Pages 261-268 in D. R. Browne, K. L. Mitchell, and H. W. Chaney, editors. Fifth California islands symposium. MBC Applied Environmental Sciences, Costa Mesa, California, USA. Wenner, A. M., R. W. Thorp and J. F. Barthell. 2000. Removal of European honey bees from the Santa Cruz Island Ecosystem. Pages 256-260 in D. R. Browne, K. L. Mitchell, and H. W. Chaney, editors. Fifth California islands symposium. MBC Applied Environmental Sciences, Costa Mesa, California, USA.

Visit #1150 @Santa Cruz Island Reserve

Approved

Under Project # 976 | Research

Island Honey Bees

faculty - University of Central Oklahoma

Reservation Members(s)

Group of 2 Faculty Jun 29 - Jul 1, 2003 (3 days)
John Barthell Jun 29 - Jul 1, 2003 (3 days)

Reserve Resources(s) | Create Invoice

Jeep 3 Jun 29 - Jul 1, 2003
Private Room 3 Jun 29 - Jul 1, 2003