Kester, Nicole2025-12-022025-12-022025-12-02http://hdl.handle.net/10393/51133https://doi.org/10.20381/ruor-31582As introduced plants continue to spread throughout North America, there is an increasing need to understand and predict their invasion patterns. Climatic niche shifts are an important aspect of invasion patterns and occur when the climatic conditions occupied in the introduced range differ from the native range. Neglecting to account for climatic niche shifts reduces the accuracy of predictions of the future distributions of introduced species, limiting our ability to proactively manage and constrain their spread. In this thesis, I examine the frequency and characteristics of climatic niche shifts, and their implications for predicting the distributions of terrestrial introduced plant species in North America. In Chapter 1, I explored how violating a key assumption (niche conservatism) in species distribution modelling affects predictions of the future distributions of invasive plant species using Vincetoxicum rossicum as a case study. I found that V. rossicum has expanded its niche in North America into wetter climates and climates where precipitation is more evenly distributed throughout the year. As a result, native- and invasive-trained models differed greatly in their predictions of climatic suitability for V. rossicum across North America. I also found that a large portion of the climate in North America was non-analogous to the current invaded range. Consequently, the native-trained model generated predictions across a larger area of North America. My study revealed the complementary nature of building both invasive- and native-trained species distribution models. Though the invasive-trained model provides predictions of the species’ potential distribution that are more representative of the invasion context (due to the niche shift), the native-trained model is able to make predictions at a much larger geographic scale. In Chapter 2, I evaluated the prevalence of climatic niche shifts in 663 introduced plants species in North America by distinguishing between conditions only occupied in the introduced range (a niche expansion) and conditions only occupied in the native range (which could indicate temporary under-filling) as different types of niche shifts. My results showed that the estimated prevalence of niche shifts more than doubles when considering both under-filling and expansion as types of niche shifts, as opposed to solely expansion. Therefore, it is important to consider under-filling and expansion separately so as to not underestimate introduced plant species’ potential distributions in their introduced ranges or overestimate the prevalence of ‘true’ niche shifts. I also quantified expansion in eight bioclimatic variables to determine under what climatic conditions expansion commonly occurs. I found that introduced plants in North America are primarily expanding into wetter climates and into climates with more seasonally variable temperature and precipitation. By improving our understanding of the niche dynamics of introduced plant species and their implications for model building, we will be able to better predict the spread of these species.enintroduced plantsinvasive speciesniche expansionniche shiftsspecies distribution modelsThesis