Date of Award:

5-2003

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Biology

Committee Chair(s)

Edward W. Evans

Committee

Edward W. Evans

Committee

Vincent J. Tepedino

Committee

Russell Mason

Abstract

Foraging studies have established that bees typically obey a set of movement rules when foraging on vertical inflorescences: they begin foraging at the bottom of an inflorescence, move upward, visit a fraction of the available flowers, and leave before reaching the top of the inflorescence. These behaviors are purported to maximize bee foraging efficiency by concentrating their efforts on the most rewarding flowers and minimizing flower revisits. Bees also increase their efficiency by selecting inflorescences with many flowers, visiting more flowers per inflorescence, and remaining in resource-rich areas. To test these hypotheses on plants with more complicated flower arrangements, I observed the foraging behavior of the solitary, specialist bee, Diadasia nigrifrons, on its host plant, Sidalcea oregana ssp. oregana, at two sites in northern Utah. S. oregana plants produce one to several paniculate (non-vertical) inflorescences. Flowers open from bottom to top within branches of the panicle, but flowering often occurs contemporaneously between branches.

Diadasia foraging behavior did not conform to the expected movement rules. Bees tended to arrive at male flowers irrespective of their position on the inflorescence, visit one or a few flowers, and leave the inflorescence and the foraging area. They did not forage from bottom to top and did not appear to favor inflorescences with more flowers. Despite this, bees did respond to differences in flower number within inflorescences by visiting more flowers on larger inflorescences. Other studies have shown that bees tend to remain foraging in an area after encountering abundant resources. In addition to flower number as a measure of reward availability, I used the foraging time on the first flower visited and the time elapsed since the flower was last visited. The response of bees to these cues was inconsistent. Bees were not more likely to remain foraging in an area after visiting an inflorescence with many flowers than after visiting one with few flowers, nor were they consistently more likely to remain foraging after visiting rewarding flowers. I discuss several possible explanations for Diadasia's apparent non-optimal foraging behavior, including the possibility that Diadasia behavior is a response to perceived predation risks and/or reward availability.

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