Date of Award:

8-2026

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Biology

Committee Chair(s)

Karen M. Kapheim

Committee

Karen M. Kapheim

Committee

Eugene Schupp

Committee

Robert N. Schaeffer

Committee

Moria Robinson

Committee

Rebecca E. Irwin

Committee

Emilie Demard

Abstract

Flowers produce nectar to attract pollinators, but nectar is also a habitat for yeasts and bacteria that arrive via pollinators, robbers, and other visitors. These microbes consume nectar sugars and release byproducts that change the smell and taste of nectar. Whether these changes affect how pollinators find and choose flowers, and whether they ultimately affect how many seeds a plant produces, is not well understood. In this dissertation, I studied how a common nectar yeast and a plant-associated bacterium affect the scent of wildflowers, the behavior of bumble bees and hummingbirds, and plant reproduction in montane meadows in central Colorado. I found that the yeast changed the scent of nectar in every flower species I tested, producing a consistent set of fermentation aromas. These yeast-produced scents also helped bumble bees that rob flowers find nectar faster through robbing holes, making them more efficient cheaters. In a separate study with hummingbird-pollinated scarlet gilia, the bacterium deterred hummingbird visits in a controlled setting, and the yeast altered pollen movement among plants in natural populations. However, neither microbe reduced seed production in the field, suggesting that pollinator behavioral changes observed in controlled experiments do not always translate to measurable effects on plant reproduction. This work shows that the invisible microbes living in nectar can influence the relationships between plants, their pollinators, and flower-robbing insects in ways that have not been previously recognized. Understanding these microbial effects is important as researchers work to understand the natural processes that sustain plant and pollinator communities.

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