Effects of disturbance on habitat dynamics of a rare species

One of the most critical tasks in conservation planning for rare and endangered species is predicting how species respond to changing landscapes. Species abundance and distribution are impacted by spatial dynamics through habitat loss and fragmentation, and temporal dynamics of processes such as disturbance and succession. Knowledge of the potential distributions of critically rare or endangered species is necessary to assess species status and to guide species recovery plans. I examined responses of a rare species, the St. Francis' satyr butterfly, Neonympha mitchellii francisci, to changing environments using a combination of empirical studies, geospatial analyses, and mathematical modeling techniques.;First I used an observational study to evaluate how an ecosystem engineer, the beaver (Castor canadensis), influenced the presence and abundance of butterfly populations by affecting species richness and composition of wetland plant communities across local and landscape scales. Specifically, I assessed whether beaver engineering affected the persistence of larval host plants of N. m. francisci and impacted butterfly distribution in addition to overall biodiversity. Through field surveys of vegetation communities in habitat types across the successional gradient, I found that engineers create habitats where critical food plants persist for N. m. francisci . Engineers also increased plant species diversity by creating a combination of patch types across the landscape. This research shows how ecosystem engineers can play a role in both the conservation of a rare species, by influencing habitat availability and determining the composition of plant communities important for an endangered insect, and of overall plant species diversity by facilitating increased habitat heterogeneity.;To predict the spatial distribution of suitable environmental characteristics for a rare species, I created a habitat model based on remotely sensed geospatial data. Using a time series of calibrated Landsat Thematic Mapper satellite images, species occurrence data, and the Maximum Entropy modeling approach, I monitored spatio-temporal changes in habitat suitability for N. m. francisci to evaluate current habitat availability and to target sites for reintroduction efforts. Model results predicted suitable butterfly habitat is widely distributed across the study area, yet most suitable sites are unoccupied. Defining habitat requirements and identifying environmental predictors of patch occupancy over time can improve recovery plans, offer adaptive management strategies to better inform conservation agencies for monitoring populations of rare and endangered species, and provide more exact criteria for species status assignment.;To further investigate effects of spatiotemporal changes in habitats on the distribution of rare species, I used a metapopulation approach. Metapopulation dynamics may depend crucially on habitat dynamics caused by disturbance and succession. While recent models have examined effects of disturbance on metapopulation size, my work is the first to evaluate impacts across different lengths of succession. To assess how landscape and species' characteristics affect metapopulation size, I used a spatially implicit patch transition model. I analyzed the effects of varying disturbance frequencies (low, moderate, and high) in different scenarios of successional length (fast, medium, slow) to cover the biological range of species' response. To assess how species sensitivity to habitat changes respond to shifting patch availability across the landscape, I compared three occupancy rules (early, late, or all habitats) and a range of colonization rates. I demonstrate that metapopulation size is influenced by a combination of factors including the speed of succession, disturbance frequency, when patches are occupied (i.e., early or late successional stages), and colonization rate. Knowledge of successional speed and colonization rates can determine whether conservation strategies should concentrate on modifying landscape structure or habitat quality. Through evaluating how species respond to environmental changes across different models of disturbance and succession, we can make better conservation and management recommendations for rare species which utilize successional habitats.