Susan E. Elliott, Ph.D.
Susan_Elliott@together.net
I study the ecology, evolution, and conservation of plant-pollinator mutualisms. I am particularly interested in how mutualisms influence coupled ecological and evolutionary processes across the landscape.
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I study the interdependence between a long-tongued bumble bee, Bombus appositus (Apidae), and a perennial wildflower, Delphinium barbeyi (Ranunculaceae), at the Rocky Mountain Biological Lab in Gothic, CO. Bombus appositus acquires most of its food from D. barbeyi, and in return, most of D. barbeyi's pollination services come from B. appositus. My research tests how sensitive these species are to changes in each other's abundances.
Plant perspective ~ I tested how seed production varies with natural and experimental levels of pollen receipt and pollinator abundance.
I found that when D. barbeyi flowers have very high pollination, they also experience high seed predation by flies. As a result, fly seed predation dampens the benefits of high pollination for seed production. If pollinators are scarce, then flowers can still produce a few seeds autogamously, without pollinators. Therefore, the plants are buffered from responding to both extreme high and extreme low pollinator abundances, and in most years, I find that flowers are saturated with pollinator visits.
Bee perspective ~ I tested how bee reproduction varies with natural and experimental variation in flower abundance (or food supply).
I found that bee reproduction is constant across meadows that vary 10-fold in flower abundance, likely because they spread their colonies out evenly so that flower availability per colony remains constant. Bees may also be unresponsive to flower abundance because they are not always food-limited. In 2006, colonies did very well and reproduction was food-limited (i.e., fed colonies had higher reproduction than control colonies). However, in 2007, colonies did very poorly and never got large enough to exhaust their floral resources. As a result, there was a surplus of flowers for bee reproduction and fed colonies did not produce significantly more offspring than control colonies.
Since there was a surplus of flowers for bee reproduction in 2007, this meant that there was shortage of bees to pollinate D. barbeyi flowers. Consequently, in contrast to previous years when flowers were saturated with pollinator visits, in 2007, there was a strong relationship between bee abundance and seed production.
Some conclusions ~ The bees and flowers do respond to each other's abundances. However, since these responses are separated in time; if one species changes in abundance, it may be many years or miles down the road, before we see an effect in the partner population. This work supports the growing evidence that to understand bee-plant interdependence, we need to incorporate broader geographic and temporal perspectives.
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Scientific articles:
Elliott, SE. Reciprocal benefits in a plant-pollinator mutualism (in prep).
Elliott, SE, and RE Irwin. Sex-ratios, abiotic resources, and seed predation overwhelm the effects of plant and pollinator densities on seed production of Delphinium barbeyi (in prep).
Elliott, SE, RE Irwin, LS Adler, and NM Williams. The nectar alkaloid, gelsemine, does not affect offspring performance of a native solitary bee, Osmia lignaria (Megachilidae). Ecological Entomology, 2008. PDF
Elliott, SE and ES Jules. 2005. Small-scale community analysis of alpine ridge vegetation in the central Sierra Nevada. Madrono 52(1): 38-45.
Popular articles/interviews:
Nature Notes, Crested Butte Radio Interview, July 2007
The underground life of bees, Crested Butte News article, September 2006
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updated February 20, 2008