UVM Theses and Dissertations
Format:
Print
Author:
Collins, Alexandra Robin
Title:
Dept./Program:
Plant Biology
Year:
2009
Degree:
PhD
Abstract:
Genotyic diversity within a species can have extended consequences for community structure but our understanding of the ecological and evolutionary implications of withinspecies genotype interactions is limited. Thus, in this body of research I aim to determine the nature of genotypic interactions within species and the implications for plant performance. I use a model invasive species, Phalaris arundinacea, which is currently invading large wetland areas of the North Eastern United States. Genotypes of P. arundinacea are useful for intraspecific studies as genotypes can be easily be cloned through repeated vegetative tillering. Here, I present five different experiments that examine the extent to which intraspecific feedbacks andlor neutral processes maintain genotypic diversity and the implications for establishment and plant performance.
First, I examined intraspecific frequency dependent feedbacks by constructing simple hexagonal arrays with target genotypes surrounded by either same, different or no genotype neighbors. I demonstrated that genotypes responded differently to changing frequency neighborhoods and fitness proxies differed in response. Second, I determined how small scale genotypic diversity neighborhood influenced invader performance and evolutionary potential under different environmental contexts. I showed that genotypic diversity did not lead to increased productivity; however, it did generate greater evolutionary potential for all fitness proxies measured under disturbed conditions. Furthermore, genotype identity was an important determinant governing intraspecific genotype interactions and different genotypes showed a range of positive and negative responses to increasing genotypic diversity.
A range of responses to different genotype neighborhoods may facilitate invasion and increase the ability of populations to respond to novel selection pressures. Third, given that individual genotype responses to different genotype neighborhoods were weak, I also determined the extent to which stochastic processes may function to structure genotypic diversity. When grown alone, genotypes were functionally equivalent and when grown in mixture the most abundant genotype was determined at random. Therefore, ecological drift occurred at the genotype level and if sufficient propagule pressure existed, diversity could be maintained at small spatial scales. Fourth, I examined P. arundinacea seed germination success under different levels of propagule pressure and disturbance regimes. Germination success was greatest under the most heavily disturbed conditions.
Additionally, I presented dose-response curves as a potential management tool. Finally, I provided a critical link with my manipulative experiments and examined the small scale genotypic diversity for three established populations. Genetic variation was greatest within rather than between populations and all three populations examined differed considerably in the small scale spatial structure of genotypes. The smallest population exhibited greater evidence for clonal growth while the older populations exhibited evidence for greater reliance on seed recruitment. My work provides a novel contribution towards understanding determinants of invasibility and the nature of intraspecific interactions. Specifically, feedbacks and stochastic processes may interplay at small spatial scales to maintain diversity at the genotype level.
First, I examined intraspecific frequency dependent feedbacks by constructing simple hexagonal arrays with target genotypes surrounded by either same, different or no genotype neighbors. I demonstrated that genotypes responded differently to changing frequency neighborhoods and fitness proxies differed in response. Second, I determined how small scale genotypic diversity neighborhood influenced invader performance and evolutionary potential under different environmental contexts. I showed that genotypic diversity did not lead to increased productivity; however, it did generate greater evolutionary potential for all fitness proxies measured under disturbed conditions. Furthermore, genotype identity was an important determinant governing intraspecific genotype interactions and different genotypes showed a range of positive and negative responses to increasing genotypic diversity.
A range of responses to different genotype neighborhoods may facilitate invasion and increase the ability of populations to respond to novel selection pressures. Third, given that individual genotype responses to different genotype neighborhoods were weak, I also determined the extent to which stochastic processes may function to structure genotypic diversity. When grown alone, genotypes were functionally equivalent and when grown in mixture the most abundant genotype was determined at random. Therefore, ecological drift occurred at the genotype level and if sufficient propagule pressure existed, diversity could be maintained at small spatial scales. Fourth, I examined P. arundinacea seed germination success under different levels of propagule pressure and disturbance regimes. Germination success was greatest under the most heavily disturbed conditions.
Additionally, I presented dose-response curves as a potential management tool. Finally, I provided a critical link with my manipulative experiments and examined the small scale genotypic diversity for three established populations. Genetic variation was greatest within rather than between populations and all three populations examined differed considerably in the small scale spatial structure of genotypes. The smallest population exhibited greater evidence for clonal growth while the older populations exhibited evidence for greater reliance on seed recruitment. My work provides a novel contribution towards understanding determinants of invasibility and the nature of intraspecific interactions. Specifically, feedbacks and stochastic processes may interplay at small spatial scales to maintain diversity at the genotype level.