Term of Award

Spring 2003

Degree Name

Master of Science in Biology

Document Type and Release Option

Thesis (restricted to Georgia Southern)

Department

Department of Biology

Committee Chair

Lorne M. Wolfe

Committee Member 1

C. Ray Chandler

Committee Member 2

Lissa M. Leege

Abstract

Biological invasions are one of the greatest threats to biodiversity. The cost of these introduced species is staggering - damages associated with introduced species cost the United States around $138 billion annually. Despite the growing appreciation of the importance of biological invasions, most research has focused solely on the ecological factors involved in the invasion process. My research examined whether the success of invasive species may be due in part to population genetic change resulting from evolution following introduction. The hypothesis was tested using the aggressive agricultural weed, Silene latifolia. Silene latifolia is native to Europe and was introduced to North Amenca 200 years ago with the spread of agriculture. It has already been shown that this plant escaped its enemies upon introduction, but it is not known whether the success of this plant has also resulted from evolutionary change post-introduction.

I used the common garden approach both in the field (Mountain Lake Biological Station, VA) and greenhouse (Georgia Southern University). The experimental design included ten plants grown from each of twenty native (European) populations and twenty introduced (North American) populations. A number of morphological, life history, and reproductive traits were measured throughout the plant's life cycle in both common gardens. Additionally, competitive ability was measured in the greenhouse. Plants from the two regions differed, with North American populations exhibiting weedier growth. On average, plants from North America germinated faster, were larger throughout the juvenile stage, and flowered earlier than plants from Europe. While increased weediness has likely contributed to the success of Silene, competitive ability does not differ between the introduced and native ranges, and therefore has not contributed to this invasion.

In addition to the evolution of the traits mentioned above, plants from North America are more successful throughout the life-cycle than those from Europe. By taking into account the probability of germination, survival, and seed production, a seed from North America has a 37% greater potential than a seed from Europe to germinate and grow into a flowering plant. This significant increase in fitness in the introduced range most likely has contributed to the increased vigor of this plant. Silene latifolia has done remarkably well since its introduction to North America. While ecological factors (i.e. the absence of enemies) have contributed to its success, genetically based differences in important traits have also played a potentially significant role in the invasion process. The findings of this research contribute to our understanding of the role of different forces in regulating biological invasions.

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