Type of Document Thesis Author Bladow, Jason Michael URN etd-11192010-101229 Title The Role of Environment and Genetics in the Demography of Introduced and Natural Populations of the Endangered Shrub Conradina Glabra Degree Master of Science Department Biological Science, Department of Advisory Committee
Advisor Name Title Alice Winn Committee Chair Austin Mast Committee Member Nora Underwood Committee Member Keywords
- Endangered Species
- Demographic Matrix Model
- Conradina glabra
- Inbreeding Depression
Date of Defense 2010-10-18 Availability unrestricted AbstractBiodiversity continues to decline as many species face extinction. One way to mitigate possible extinction is to introduce new populations of a species to locations that the species does not currently occupy. Such introductions can sometimes fail due to environmental factors or to genetic problems that may arise from small population size. Monitoring introduced populations and collecting data can identify reasons for the success or failure of an introduction and provide valuable information for future management efforts. To evaluate the success of introductions, demographic models can be constructed and analyzed to determine if populations are growing and to identify parts of the life cycle that contribute most to the population growth rate.
Conradina glabra is an endangered shrub that was introduced to three sites at the Apalachicola Bluffs and Ravines Preserve in Liberty County, Florida 1991. Three introduced populations and three natural populations were censused in 2009 and 2010 to construct stage-structured demographic models to project the current growth rates of the introduced populations and to compare them to natural populations. Sensitivity and elasticity analyses were performed to determine the importance of individual rates of growth, survival, and seed production to the overall success of each population. A Life Table Response Experiment analysis was conducted to determine how much differences in each of these vital rates contributed to the observed difference in the growth rate between introduced and natural populations.
All of the populations examined were projected to grow or remain stable (λ ≥ 1) indicating that the introduced and natural populations are projected to be successful. As a whole, introduced populations grew faster (λ = 1.052) than natural populations (λ = 1.004). Stasis of large plants, or the proportion of large plants that survived and remained in the same stage class from one year to the next, was the most important vital rate in maintaining the population growth rate for both introduced and natural populations. Greater growth in early life stages and greater fecundity contributed to the greater population growth rate at introduced populations, while increased regression of larger plants to smaller plants and the stasis of young individuals contributed to the lower growth rate of natural populations.
A second experiment looked for evidence of inbreeding depression in C. glabra. Flowers in one natural and one introduced population were hand selfed or outcrossed to estimate inbreeding depression in seed set, seed weight, and germination rate. Inbreeding depression in the number seeds produced per flower and percentage seed germination was significant. Outcrossed flowers produced 1.5 seeds on average, compared to 1.04 seeds per flower from selfed crosses. Seeds from outcrossed flowers germinated at a rate of 12% while seeds from selfed flowers germinated at a rate of 4.1%. There was no evidence of inbreeding depression in seed mass.
The effects of inbreeding were incorporated into demographic models for the introduced and natural populations that assumed that all seed production was a result of selfing. This hypothetical scenario was compared to the models for unmanipulated populations to examine the potential effects of extreme inbreeding on the demography of C. glabra. When demographic models included the effects of inbreeding depression, the population growth rate became less than one, indicating that populations would decline if they become entirely selfing.
At present, all populations are projected to remain stable or grow, although the timeframe over which data were collected was short relative to the lifetime of individuals, and the predicted success of populations is conditional upon the assumption that estimates of the vital rates accurately reflect long-term rates of growth, survival, and reproduction. Inbreeding depression can occur in these populations and is a threat that should be considered when introducing populations, even though at this time, C. glabra populations are growing despite the potential for inbreeding depression.
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