Date of Award:

5-1-1998

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Biology

Committee Chair(s)

James A. MacMahon

Committee

James A. MacMahon

Committee

Janis L. Boettinger

Committee

Vincent J. Tepedino

Abstract

The management of a rare, edaphic endemic plant species requires an understanding of the ecological setting and processes that contribute to its restriction. Included in the ecological processes is a set of biotic characters associated with the reproductive ecology, including its breeding system, pollination vectors, and germination requirements. The geologic and soil setting of the plant must also be characterized in order to understand the plant's restriction to the substrate. These issues were addressed by this study of the rare endemic Penstemon debilis O'Kane and Anderson (Scrophulariaceae). Penstemon debilis consists of six populations that occur on talus slopes of the Parachute Creek member of the Green River Oil Shale formation in Garfield County, Colorado. Results from breeding system experiments and pollinator observations indicate that P. debilis is primarily an outcrossing species and requires an insect pollinator to set fruit. The results also indicate that fruit and seed set are not pollen or pollinator limited, and the main pollinators, mason bees and a species of wasp, are neither rare nor P. debilis specialists. Germination experiments revealed that the seeds are dormant and require a period of moist-chilling to break dormancy, and that the seedlings do not require native shale soil for growth and establishment. Soil analyses reveal significant variation in soil chemistry among population sites, indicating that the soil chemistry is probably not a direct factor in the endemism of this species. However, population sites were very similar with respect to physical characteristics such as degree of natural disturbance, depth to bedrock, percentage of coarse material, slope, and surface rock fragments. Knowledge of such characteristics may help managers predict where undiscovered populations already occur, or where new populations could be established if the conservation need arises.

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