Thesis (M.Sc.) - Carleton University, 2005. / Includes bibliographical references. Also available in electronic format on the Internet.

Invasive plant species are an increasing global threat to native biodiversity. Effective management depends on accurate predictions of their spread. However, modelling the geographic distribution of invasive species, particularly with methods like correlative species distribution models (SDMs), is challenging. SDMs operate under the assumption that species are in equilibrium with their environment (i.e., they occur in all suitable environments); this assumption is more likely to be violated for a species that is still in the process of colonizing suitable environments. SDMs also assume that environmental constraints are the most important factors determining a species' distribution. However, these assumptions are not commonly assessed, and when violated can have consequences for model reliability. I investigated SDM performance and equilibrium in the invasive Vincetoxicum rossicum vine in northeastern North America. Vincetoxicum rossicum has a long, detailed history of occurrence records in its invaded range, which enabled me to observe trends in equilibrium and model performance over a relatively long time scale. I tested the hypotheses that: 1) invasive species approach equilibrium in environmental and geographic space over time; 2) SDM performance will increase as V. rossicum approaches environmental equilibrium; and 3) range expansion in the early stages of an invasion is primarily a function of dispersal rather than environmental constraints, while the reverse is true in later stages. I found that V. rossicum has reached equilibrium in environmental space, but is still expanding its geographic range. SDM performance was poor in the first 30 years following introduction, but then improved as V. rossicum approached environmental equilibrium. SDMs were outperformed by spatial dispersal models in the earliest time period, however, the reverse was true for all subsequent time periods. Overall, these results suggest that V. rossicum’s distribution is becoming more stable and more predictable over time and that models built using the most recent data for this species, will be the most transferable across time and space. Additionally, my findings highlight the need for researchers modelling invasive species’ distributions to consider the inherent assumptions, biases, and unique features related to SDMs and SDMs of invasive species.

Soil fungi play an important role in regulating plant communities as well as above and below ground ecosystem-level processes; conversely, plant communities may also affect the structure and functionality of these root-associating fungi. Alteration of these fungal communities due to non-native plant invasion has the potential to disrupt biogeochemical cycling, soil structure, and plant growth. Both beneficial symbionts such as arbuscular mycorrhizal fungi (AMF) as well as the total fungal community are potentially altered by aggressive invasive plant species in such a way as to disrupt existing native endophytic fungal communities in the soil post invasion. This disruption could provide a pathway for invasion and suggests the importance of investigating plant-fungal associations in invaded ranges. I used molecular techniques to characterize the fungal communities colonizing Vincetoxicum rossicum or Dog-strangling vine (DSV) and Alliaria petiolata or garlic mustard, both European natives that are currently well established in Eastern North America, as well as native plants that are commonly found persisting in the presence of dense colonies of DSV, as well as those same natives growing separately from DSV. Fungi colonizing different plant groups were analyzed using primers that target the internal transcribed spacer region of the ribosomal operon in order to amplify total fungal species (TF), as well as primers designed to exclusively amplify AMF using small subunit rRNA sequences. Significant differences were observed in the diversity of both the TF and the AMF communities colonizing native plants in the invaded sites relative to the uninvaded sites. Sequencing work indicated that DSV forms associations with a broad array of fungal partners relative to proximal native plants, suggesting the likelihood of it being a fungal generalist. As well, DSV was found to associate with described opportunistic AMF such as Glomus intraradices, G. caledonium, G. fasciculatum and G. mosseae, while natives growing within DSV patches were not. Finally, garlic mustard was found to have the dominant effect where DSV and garlic mustard were co-occurring. These findings support the ongoing investigations into plant invasion processes, and therefore contribute to the development of effective strategies for invasive species management as well as site restoration techniques.

Soil fungi play an important role in regulating plant communities as well as above and below ground ecosystem-level processes; conversely, plant communities may also affect the structure and functionality of these root-associating fungi. Alteration of these fungal communities due to non-native plant invasion has the potential to disrupt biogeochemical cycling, soil structure, and plant growth. Both beneficial symbionts such as arbuscular mycorrhizal fungi (AMF) as well as the total fungal community are potentially altered by aggressive invasive plant species in such a way as to disrupt existing native endophytic fungal communities in the soil post invasion. This disruption could provide a pathway for invasion and suggests the importance of investigating plant-fungal associations in invaded ranges. I used molecular techniques to characterize the fungal communities colonizing Vincetoxicum rossicum or Dog-strangling vine (DSV) and Alliaria petiolata or garlic mustard, both European natives that are currently well established in Eastern North America, as well as native plants that are commonly found persisting in the presence of dense colonies of DSV, as well as those same natives growing separately from DSV. Fungi colonizing different plant groups were analyzed using primers that target the internal transcribed spacer region of the ribosomal operon in order to amplify total fungal species (TF), as well as primers designed to exclusively amplify AMF using small subunit rRNA sequences. Significant differences were observed in the diversity of both the TF and the AMF communities colonizing native plants in the invaded sites relative to the uninvaded sites. Sequencing work indicated that DSV forms associations with a broad array of fungal partners relative to proximal native plants, suggesting the likelihood of it being a fungal generalist. As well, DSV was found to associate with described opportunistic AMF such as Glomus intraradices, G. caledonium, G. fasciculatum and G. mosseae, while natives growing within DSV patches were not. Finally, garlic mustard was found to have the dominant effect where DSV and garlic mustard were co-occurring. These findings support the ongoing investigations into plant invasion processes, and therefore contribute to the development of effective strategies for invasive species management as well as site restoration techniques.