Date of Award:
5-1-1998
Document Type:
Thesis
Degree Name:
Master of Science (MS)
Department:
Biology
Committee Chair(s)
Vincent J. Tepedino
Committee
Vincent J. Tepedino
Committee
Eugene W. Schupp
Committee
Diane G. Alston
Abstract
I examined the reproductive biology of Harrington's Penstemon, a rare endemic of the Colorado Plateau, to obtain information important to conservation efforts for this species. I applied four different hand-pollination treatments to P. harringtonii's flowers and found that it is partially self-compatible but sets more fruits when cross-pollinated by insects. Plant placement in new populations may be important because pollinators are more attracted to dense floral resources. Thus, the fruit set of plants within a 450 cm2 area was compared with those at least 3 m apart. Unexpectedly, aggregated plants produced 16.1 fruits per plant compared to 21.0 for plants farther apart, suggesting that aggregated plants suffered from either inbreeding depression or resource competition. Percent fruit sets were also regressed on distances of nearest conspecific neighbors. No relationship was found at either site between neighbor distance and percent fruit set, suggesting that plants with distant neighbors received enough pollinator visits. Despite its reliance on insects for reproductive success, P. harringtonii was resource- rather than pollen-limited: Plants supplemented with pollen (68%) did not differ from naturally pollinated plants (66%). Plants growing within sagebrush canopies produced more fruits at the tops of inflorences than at lower positions, while plants in the open produced fewer fruits at their tops and more at lower positons. However, total fruit set did not differ between sagebrush sheltered and open plants, suggesting that sagebrush neither competed with nor aided P. harringtonii plants, and that again, plants were not pollen-limited. Comparisons of fruit set among different elevations showed that growing time may be limiting. Though plants at lower elevations in 1993 were larger and produced more flowers and fruits than plants at higher elevations, percent fruit sets did not differ. Visitation observations demonstrated that though bees in the family Megachilidae and wasps in the family Masaridae were the primary pollinators, species composition and flower-visitation rates sometimes varied dramatically between sites and years. Evidently, pollinator redunancy attributed to the high percent fruit sets P. harringtonii produced both years.
Recommended Citation
Nielson, Romaine L., "The Reproductive Biology and Ecology of Penstemon harringtonii (Scrophulariacea): Implications for Conservation" (1998). Biology. 654.
https://digitalcommons.usu.edu/etd_biology/654
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