Biology Ph.D. Dissertations

Pollination Ecology and Demography of a Deceptive Orchid

Date of Award

2013

Document Type

Dissertation

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Biological Sciences

First Advisor

Helen Michaels

Second Advisor

Timothy Murnen (Committee Member)

Third Advisor

Moira van Staaden (Committee Member)

Fourth Advisor

Karen Root (Committee Member)

Fifth Advisor

Randy Mitchell (Committee Member)

Abstract

This dissertation is focused on three main questions addressing the reproductive and demographic effects of pollen limitation, seed predation and deceit pollination in the food deceptive orchid Cypripedium candidum. We conducted two hand pollination field experiments to quantify pollen limitation and inbreeding. Both studies showed strong pollen limitation, with supplemental hand pollinations increasing fruit set in 2009 by 41% and 2011 by 30-35%. Taller plants in the study were more likely to be pollinated, while all other size variables did not influence pollination or fruit set. The 2011 study demonstrated a reduction in seed mass in selfed capsules by 63%. We found high levels of fruit predation in 2009 with 73% of the fruit experiencing pre-dispersal seed predation resulting in an 89% reduction in seed mass. Of the size variables analyzed, shorter plants were more likely to be attacked by weevils. In a nectar addition study we manipulated plants to provide a nectar reward, dyed their pollinia for tracking and compared their reproduction against control plants with no reward. Nectar reward, which had no effect on fruit production, however did result in a nearly threefold increase in selfing. Approximately 26% of non-rewarding C. candidum pollination events result in selfing, while the addition of nectar increased selfing to 78%. Selfed seed capsules had a decreased seed mass as demonstrated in the previous experiment. Finally, we conducted a four year demographic study and produced matrix models that estimated the population growth rate at λ = 1.01 under an average of 22% pre-dispersal seed predation. Elasticity values of the models indicated the stasis and growth of one-flowered individuals to be the most important factors to the population growth rate. A model simulating the effects of nectar addition with the average rate of seed predation resulted in λ = 0.99. These studies demonstrate the complex reproductive dynamics of deceptive plants and provide evidence suggesting the evolution of deceit pollination is driven by multiple factors, including predation and decreased fecundity from selfing.

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