Undergraduate Honors Theses

Thesis Defended

Spring 2018

Document Type


Type of Thesis

Departmental Honors


Ecology and Evolutionary Biology

First Advisor

Dr. Erin Tripp


Two distantly related species of Penstemon, Penstemon virens and Penstemon secundiflorus frequently flower contemporaneously throughout an overlapping range in the foothills and Front Range of Colorado. In cases where populations are sympatric (co-occurring) and hybrids do not form, non-geographic and non-temporal boundaries must be present that limit or prohibit gene flow between species. I examined two possible contributors to such boundaries, pollinator activity and floral traits, through a field pollination experiment in the foothills of central Colorado in the summer of 2016 and found that both species exhibit distinctive floral traits that may affect both pollinator behavior and mechanical compatibility. Field collection of floral visitors (totaling 68 individuals) indicated that only five bee species from two genera (Lasioglossum and Hylaeus) were shared between P. virens and P. secundiflorus, suggesting that pollinator behavior contributes to limiting gene flow between these two species. Thus, the limited overlap in pollinator species and floral morphology likely severely limit the capacity for hybridization between these two species of Penstemon. Finally, I found that floral traits could not be used to predict floral visitors in a way that is consistent with prior research on pollination syndromes in the genus of Penstemon. Further field research in pollination ecology is needed to assess pollinator behavior in response to the variety of floral traits exhibited in the genus and to assess the fitness and life history of these two iconic flowering-plant species of the Colorado foothills.