| Summary: | Correlative ecological niche models, built with species’ occurrence records, have become the most widespread methods to forecast range shifts with climate change, but these models assume species’ range limits are driven by their niche limits. If a species range limit is instead the result of dispersal limitation, then these correlative based models will be poorly calibrated and largely inaccurate. I used experimental field transplants within and beyond the northern range limit of the scarlet monkeyflower (Mimulus cardinalis) to test for dispersal limitation and to see if climatic-based ecological niche models were able to accurately predict site-level suitability. I also compared predictions from the niche models to a previous study that transplanted the species beyond its upper elevational range limit, which is known to be fitness limited rather than dispersal limited. Predictions from the niche model closely matched observed fitness from the field transplant experiment across the species’ elevational range limit, but not across the species’ northern latitudinal range limit. Consistently high fitness was maintained within and beyond the northern range limit and even in sites of low predicted suitability, suggesting the northern range limit is dispersal limited. I then constructed an alternative ecological niche model for M. cardinalis with stream habitat variables, rather than climatic variables and controlled for the influence of climatic mechanistically, with a simple thermal envelope. This alternative model demonstrated a large amount of suitable habitat beyond the northern range limit, further supporting that this range limit is largely dispersal limited rather than fitness limited. Dispersal limitation presents a serious systemic challenge for the correlative niche modeling framework and its associated applications. By combining niche models with field experiments, I was able to show both the strengths and weaknesses of these methods and use existing theory of dispersal limitation as a framework to assess the accuracy of these models. === Science, Faculty of === Botany, Department of === Graduate
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