Date of Award

Fall 12-1-2003

Document Type

Thesis

Degree Name

Master of Arts (MA)

Department

Life Sciences

First Advisor

Peter E. Scott

Second Advisor

Steven L. Lima

Third Advisor

Elaina M. Tuttle

Abstract

Native forest wildflowers of the Midwestern United States forests now compete with agricultural weeds for the attention of insect pollinators. The tiny quantities of nectar secreted by these insect-pollinated flowers are measured using laboratory techniques such as colorimetry. However, these techniques are used with the tacit assumption that nectar sugar identity does not affect estimates of carbohydrate content. I tested this hypothesis using fructose, glucose, and sucrose and found that after reaction with anthrone, fructose products differed from those of other sugars in light absorbance measured by a spectrophotometer. Potential error from using an inappropriate sugar standard is greater than has been assumed. To reduce error, the nectar sugars of a plant population should be identified and their proportions determined before quantification with colorimetry. I used high performance liquid chromatography and spectrophotometry to characterize the nectar of five common spring flowers of forest and agricultural fields (Erigenia bulbosa, Claytonia virginica, Cardamine concatenata, Stellaria media, and Barbarea vulgaris). Nectar chemistry was similar across species: fructose was ubiquitous. However, when present, glucose and sucrose occurred in significantly greater amounts than fructose. Mean daily sugar production per flower varied with flower size. Production rates of the two weed species overlapped with two of three forest species. Nectar of all five species was fairly well harvested, consistent with previous observations at these sites of bee and fly species foraging in both habitats. I also estimated the effects IV of site, date, and plant identity on daily sugar production of each species. Most variance was due to individual plant differences. A three-fold difference in production rate between flowers at the 25th and 75th percentiles was typical, indicating that insect pollinators encounter much variation even if they specialize on a flower species.

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