Heather G. McGray

research

Heather G. McGraY

Avena

The Effects of Genetic Diversity on Invasive Species Success
	Biodiversity can positively affect a system’s performance and function, provides many human services, and manifests across many levels of organization including functional diversity within an ecosystem, species diversity within a community, and genetic diversity within a population. While diversity effects at the ecosystem and community level are well studied, an understanding of their importance at the population level is just beginning to emerge. Species invasions present an interesting system for examining diversity effects at the population level because diversity is predicted to have large impacts on the success of a invading populations. Additionally, there are no direct tests of the importance of invasive population genetic diversity to invasive success. The genetic diversity of a population should profoundly affect its success. Positive diversity effects are proposed to occur via complementarity effects when increased diversity decreases intra-specific competition and increases resource partitioning, allowing for more efficient and complete resource use. Sampling effects occur when increased diversity increases the chance a system contains a highly functioning or productive species. Finally, environmental selection alters genetic diversity of a population over time.
		In contrast to species diversity research, tests of the influence of genetic diversity on population success are rare. There is little understanding of the relative importance of their underlying mechanisms. In addition, the interactive effects of ecological mechanisms that promote these effects and evolutionary change are untested. In order to directly address the importance of these mechanisms and their interactive effects, my research proposes to determine how genetic diversity affects invasive population success across different environments. It aims to test the following hypotheses: Increased genetic diversity of an invasive population leads to increased invasion success. The relative strengths of the ecological mechanisms that promote invasion success through genetic diversity will change depending on environment. Complementarity effects are predicted to be stronger in heterogeneous environments due to resource partitioning where as sampling effects are predicted be stronger in homogenous environments due to an increase in the probability of the presence of highly fit genotypes.
	Evolutionary processes will differentially alter genetic diversity depending on environmental heterogeneity. Balancing selection will occur in heterogeneous environments and directional selection will occur in more homogenous environments. The ecological mechanisms that promote invasion success through genetic diversity will interact with environmental selection over time. Balancing selection in heterogeneous environments is predicted to maintain genetic diversity and reinforce complementarity effects over time. Directional selection in homogenous environments is predicted to decrease genetic diversity and reinforce sampling effects over time. To test these hypotheses, the genetic diversity of invasive Avena barbata* populations is directly manipulated. These populations are grown under homogenous and heterogeneous resource environments. Populations are grown in mesocosms under controlled conditions to examine the relative importance of ecological and evolutionary mechanisms (and their interactions) on invasive success over time. In addition, resident communities will be invaded by experimental populations in order to examine these questions under natural invasive conditions.
	* I would like to acknowledge and thank Dr. Robert Latta from Dalhousie University for use of the Avena barbata recombinant inbred lines that make this work possible.