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Open Access Dissertation
Doctor of Philosophy (PhD)
Organismic and Evolutionary Biology
Year Degree Awarded
Month Degree Awarded
Bethany A. Bradley
Other Ecology and Evolutionary Biology
Anthropogenically-driven changes threaten ecosystems and species over regional to global scales. I addressed several questions related to how species ranges will respond to these changes over large spatial and temporal extents to better understand what determines where a species occurs.
First, I modeled presence and abundance of two widespread invasive plants in the southwest U.S. under current and projected future climatic conditions, from which I inferred impact risk. These results provide more insight than presence modeling alone and highlight the possibility of increased invasion pressure in the future.
Second, I tested the assumption that expert-based climatic tolerance data will better reflect a species’ physiological constraints than widely available herbarium data. I compared climatic ranges derived from herbarium data to those from expert-based data for over 1,800 terrestrial plant species. This research indicates that herbarium records provide more robust estimates of climatic tolerance, especially for widespread forbs and grasses.
Third, I leveraged a unique spatial percent cover dataset to model potential sagebrush cover under current and future climate in the western U.S. The sagebrush ecosystem characterizes shrublands of the intermountain western U.S. and provides habitat for many obligate species but is threatened by several forms of global change. We used potential sagebrush cover to estimate habitat for five sagebrush-obligate species. The results identify regions most likely to support sagebrush and sagebrush-obligate species in the context of climate change.
Finally, I addressed questions related to the spatial extent and landscape configuration of non-native Pinus in Chile. Pinus species are used in large plantations but have spread into surrounding landscapes and established invasive populations. In southern Chile, the extent of plantations and invasion is unknown, although the threat of invasion is well documented. Results from this study suggest that: 1) areas with high relief and high or low elevation might be less invasion-prone; 2) invasion risk might be lower than assumed given the prevalence of invasion-resistant native forest; and 3) the landscape should be monitored for new invasion sites stemming from isolated pine patches.
Curtis, Caroline, "MODELING THE ABUNDANCE AND DISTRIBUTION OF TERRESTRIAL PLANTS THROUGH SPACE AND TIME" (2018). Doctoral Dissertations. 1435.