Date of Award:

5-1999

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Biology

Committee Chair(s)

Mary Barkworth (Committee Chair), Vincent J. Tepedino (Committee Co-Chair)

Committee

Mary Barkworth

Committee

Vincent J. Tepedino

Committee

Janis L. Boettinger

Abstract

I examined the reproductive biology and general ecology of Saxifraga bryophora var. tobiasiae, a rare saxifrage endemic to the West Salmon River Mountains of central Idaho. Saxifraga bryophora var. tobiasiae combines asexual reproduction via bulbils with a sexual mixed-mating system. Flower production occurred in 1996 only, whereas bulbil production occurred in 1995, 1996, and 1997. Bulbil production precedes floral bud formation and is the dominant form of reproduction. When flowering occurs, outcrossing is promoted by protandry and the gynodioecious mating system found in all populations. No autogamous or agamospermous seed set was observed in either female or hermaphrodite flowers, indicating that a pollen vector is required for reproduction. Hermaphrodites were self-compatible but none automatically self-pollinated. Pollinator visitation was extremely low, but this did not significantly affect fruit set. Flower visitors were infrequent and consisted mostly of syrphids (Diptera: Syrphidae) and empidids (Diptera: Empididae). Female plants produced significantly more bulbils than hermaphrodites. Females may be maintained in the population for this reason.

The populations of Saxifraga bryophora var. tobiasiae were thoroughly surveyed to identify actual and potential habitat. Twenty-eight soil pits in actual and potential S. bryophora var. tobiasiae habitat were described. Soils were classified as Lithic Cryoborolls, Lithic Cryochrepts, and Lithic Cryorthents. The physical characteristics of these soils were very similar among habitat and non-habitat sites, but higher rock fragments were found in soils with S. bryophora var. tobiasiae. The shallow soils and natural disturbance from runoff influence the narrow distribution and rarity of this taxon. Classification tree analysis was used to determine which ecological factors were useful in predicting S. bryophora var. tobiasiae presence. Bare soil, Lewisia triphylla, Erythronium grandiflorum, Vaccinium scoparium, and Polytrichum juniperinum were significant predictors of S. bryophora var. tobiasiae. The findings of this study provide biological and ecological information about S. bryophora var. tobiasiae that may be useful to managers in attempting to conserve this rare taxon and the habitat in which it exists.

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