Semester

Spring

Date of Graduation

2004

Document Type

Dissertation

Degree Type

PhD

College

Eberly College of Arts and Sciences

Department

Biology

Committee Chair

James B. McGraw.

Abstract

Hydrastis canadensis L. (goldenseal) is becoming more uncommon within the eastern deciduous forest. I performed a series of studies that tested hypotheses about population decline and causes of rarity. First, I assessed the time-trend of a natural H. canadensis population in an Indiana nature preserve which had been censused 26 years prior. We found a negative population trajectory between the two time periods. The second goal of this dissertation was to determine the breeding system of H. canadensis. The breeding system type appears unlikely to be a major factor limiting the distribution or abundance of H. canadensis. My third objective was to assess the response of H. canadensis populations to harvest. I found variation in patch regrowth which suggests timing of harvest may be important. My studies in chapter 5 focused on abiotic microsite factors. I experimentally assessed the role of temperature, humidity, and light gradients in the distribution of H. canadensis. The relatively weak association between environmental variation and plant performance across the forested cove reinforces other studies suggesting that H. canadensis has a relatively broad ecological niche, and its rarity is unlikely due to availability of suitable abiotic habitat conditions. My fifth goal was to understand ecologically relevant aspects of H. canadensis genetics. I determined if H. canadensis contained ecologically important genetic variation (i.e. ecotypic differentiation) at the population level. I conducted a classical reciprocal transplant experiment with four natural populations to test the hypothesis that ramets planted in their home site would have greater survival and performance than alien H. canadensis ramets planted into the same site. This research is the basis of Chapter 6. My final goal was to determine whether H. canadensis range is limited due to high habitat specificity and limited availability of suitable habitat. This study found no evidence of a lack of suitable habitat for H. canadensis. Overall, these studies serve to rule out several possible causes of rarity of H. canadensis, although this research does suggest some role of understory light availability in species decline. This idea, along with other hypotheses, is discussed further in the general conclusions.

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