Santa Cruz Island Reserve

02 Aug, 05 AM - 05 Aug, 05 AM

STATEMENT OF PROPOSED PURPOSE: Processes underlying biological invasions are poorly understood but are generating increased interest among ecologists, with deep implications for the conservation of our native and agricultural systems. During the last two years we began testing predictions about competition between non-native and native plants on Santa Cruz Island (SCI), California, and on the island of Lesbos in the Northern Aegean. The proposed project has both SCI- and Lesbos-based components involving collaboration between faculty and students from the National Science Foundation's REU Program. Preliminary results from this collaboration show that competition between native gumplant (Grindelia camporum) and the non-native yellow star-thistle (Centaurea solstitialis) reduces the number of pollinators to the native plant on SCI (and we wish to pursue this hypothesis in Greece as well). This proposal examines how ?nectar standing crop? (a measure of nectar availability to pollinators) mediates competition between native and non-native plants as well as population structure of a specialist pollinator, Megachile apicalis. PROJECT DESCRIPTION: Conceptual Model and Predictions. We continue to test predictions generated by a conceptual model that outlines ?negative? (competitive) and ?positive? (mutualistic) interactions between native and non-native plant and pollinator species. These interactions are summarized below along with reference to studies (including one completed during the last year) that support the model as a tool for understanding invasions. Negative Interactions. A basic premise of the proposed study is that nectar, a primary attractant to pollinators, is an important component affecting competitive outcomes between non-native and native plants. As predicted by Ghazoul (2002), high nectar quantity and quality may mediate competition in favor of invasive plant species, a prediction now supported by a few seminal studies (Brown et al. 2002, Chittka and Sch?rkens 2001). Our preliminary results (described below) demonstrate that this pathway is indeed relevant to our study system on Santa Cruz Island (SCI), California. An additional prediction resulting from this pathway is that the reproductive capacity of the native plant species is reduced by the loss of native pollinators (which would ordinarily pollinate the plant) to the non-native plant species. (Pathways indicated above and below, are indicated as a figure which is available as an attachment). Positive Interactions. Other interaction pathways delineate mutualistic interactions that exist after invasion by non-native plants and pollinators. In previous studies based out of SCI non-native bees and plants have been shown to assist one another in newly invaded environments whereas there is less cross-over between non-native and native mutualists (Barthell et al. 2000 and 2001). Having established (in part from last year?s funding) that the highly invasive plant species yellow star-thistle, Centaurea solstitialis L., does effectively compete against the native gumplant, Grindelia camporum Greene, in its ability to attract native pollinators and an additional prediction is now proposed, below. In addition, we will collect specimens of Megachile apicalis at plants for a preliminary examination of the population genetic structure of this bee in California and Greece. Hypothesis: Nectar standing crop in flowers alters foraging behavior among bees with the consequence that native plant species, in competition with high nectar-secreting non-native species, will decrease their reproductive capacity. Prediction: The dominant native bees on Santa Cruz Island, California, in the families Anthophoridae, Halictidae and Megachilidae will alter their foraging behavior in response to the nectar standing crop among actual flowers. Background. During the last year, new results have been obtained to support our hypothesis that competitive effects exist between native and non-native plants on SCI. It is now established that the non-native yellow star-thistle does draw pollinators away from native gumplant. An experiment (conducted last summer) shows that the presence of thistle plants imported into an experimental plot, when paired with native gumplant, led to decreased pollinator visitation to the native plant relative to control pairings of gumplant. This result (yielded ahead of schedule) assures a good basis for the predictions made in this proposal. Study Organisms. Santa Cruz Island. We have now identified two plant species for experimental work on Santa Cruz Island: 1) the native gumplant, Grindelia camporum Greene, and 2) the non-native yellow star-thistle, Centaurea solstitialis L. In addition to our experimental work conducted last year (see above results), we have utilized these species in previous experiments on SCI (Barthell et al. 2000) and are confident of their flowering phenology and pollinator guilds (Thorp et al. 2000 and 1994, Junak 1995). Several native bee species in the families Anthophoridae, Halictidae and Megachilidae are available for the foraging predictions outlined below. Within the Anthophoridae the primary candidate for study is a species in the genus Melissodes whereas within the Halictidae the conspicuous and large-bodied Augochlorella pomoniella (Cockerell), Agapostemon texanus Cresson and Halictus farinosus Smith are ideal candidates. Another species in the genus Ashmeadiella (family Megachilidae) is a common (though smaller bodied) visitor to flowering plants on SCI. LITERATURE CITED: Brown, B. J., R. J. Mitchell and S. A. Graham. 2002. Competition for pollination between an invasive species (purple loosestrife) and a native congener. Ecology. 83: 2328-2336. Chittka, L. and S. Sch?rkens. 2001. Successful invasion of a floral market. Nature. 411: 653. Ghazoul, J. 2002. Flowers at the front line of invasion? Ecological Entomology. 27: 638-640. Junak, S. T., T. Ayers, R. Taylor, R. Scott, D. Wilken and D. Young. 1995. A flora of Santa Cruz Island. Santa Barbara Botanical Garden, Santa Barbara, California. 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 (eds.), Fourth California Islands Symposium: Update on Resources. Santa Barbara Museum of Natural History, Santa Barbara, California. 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 (eds.), Fifth California Islands Symposium. Santa Barbara Museum of Natural History, Santa Barbara, California. MBC Applied Environmental Sciences.

Visit #12914 @Santa Cruz Island Reserve

Approved

Under Project # 5657 | Research

Competition and Mutualism in Invasion: Testing Two Predictions through Pollinator Foraging Experiments

faculty - University of Central Oklahoma

Reservation Members(s)

Group of 3 Faculty Aug 2 - 5, 2007 (4 days)
Group of 2 Undergraduate Student Aug 2 - 5, 2007 (4 days)

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Dorm 5 Aug 2 - 5, 2007
Jeep 5 Aug 2 - 5, 2007
Private Room 5 Aug 2 - 5, 2007