| Edaphic endemic plants are of conservation concern because they often occur in small populations within unique ecosystems, and many have special conservation status. Identifying suitable habitat for their conservation is challenging because they are adapted to patchily distributed, specialized habitat conditions. Species that rely on disturbance during their life-cycle pose an additional challenge because habitat conditions vary temporally. I conducted three studies to examine the importance of habitat attributes to the occupancy, abundance, and reproductive output of four rare, disturbance-dependent, soil-specialist plants in the Pine Hill gabbro region, El Dorado County, California. In doing so I evaluated methods for predicting habitat suitability. I collected field data, including vegetation composition and structure, abiotic environmental conditions, disturbance history, and spatial habitat configuration at 106 plots, both occupied and unoccupied by rare plants, throughout the region. I quantified reproductive output at a subset of these, and also extensively mapped the distributions of the rare plants.;First, I evaluated the ability of a species distribution model, Maxent, to predict habitat suitability. Maxent models successfully discriminated between suitable and unsuitable habitat at a local scale for all four species, and ranked habitat quality based on likelihood of occurrence for three species. However, model evaluation metrics showed that predictions varied based on model selection criteria. Second, I evaluated predictions of habitat suitability based on separate analyses of abundance and occupancy patterns. Predictors of occupancy and abundance differed 87% of the time, indicating that analyses based on occupancy or abundance may reach disparate conclusions about conservation priorities. Evaluating abundance and occupancy separately may provide insight into different processes driving local and regional population persistence. Third, I evaluated the importance of habitat conditions to reproductive output. I found Allee effects, in which individual fitness was positively related to population density, in all three species examined. The Allee effects were modulated by habitat conditions, including vegetation composition and disturbance history, in all cases. Therefore, although population size is important to reproductive success, habitat quality is also a key determinant of reproductive output. Results indicated that habitat management, especially fire, may be beneficial for these populations. |
