A large-scale multi-seasonal habitat prioritization and an analysis of structural connectivity for the conservation of greater sage-grouse in Wyoming

摘要

Habitat loss is widely recognized as the primary cause of global declines in biodiversity and is linked to human disturbances through widespread land-use changes (Menon et al., 2001). As a consequence, wildlife species must persist on landscapes that are greatly modified and fragmented (Moilanen et al., 2005). Disruptions affecting the structural connectivity can hinder ecological flows of energy, nutrients and the natural dispersal of species across the landscape. Therefore, in order to conserve wildlife populations, we are challenged with securing areas where species are most likely to survive in the long run while maintaining habitat connectivity to facilitate natural ecological processes and meta-population dynamics (Gardner et al., 1993; Early and Thomas, 2007). Identifying conservation priority areas is an essential step in wildlife conservation planning. In order to achieve long term conservation success amid increasing developments and environmental degradation, we must aim for biologically and ecologically comprehensive and justifiable approaches that take multiple factors into consideration when defining conservation priority areas. In addition, when prioritizing the landscape, we must also account for the variations in habitat use caused by seasonal changes throughout the annual cycle in order to protect indispensable habitat across all seasons and life-stages. Thus, my first objective was to develop an annual habitat prioritization for greater sage-grouse (Centrocercus urophasianus; hereafter sage-grouse) in Wyoming, USA by combining nesting, summer and winter habitat selection models in an ecologically meaningful way using a quantitative spatial prioritization tool. I assessed the capacity of Wyoming’s current sage-grouse protected areas for capturing priority areas across the full annual cycle in order to quantify the importance of a multi-seasonal (i.e., annual) habitat prioritization. While, the annual habitat prioritized substantial as well as very similar fractions of the best habitat from each individual season, results indicated that the protected areas did not account for 52% of the top 25% of best annual habitat. As expected, the individual seasonal analysis confirmed that the protected areas contained more nesting priority habitat and failed to capture substantial fractions of summer and winter priority habitat. My second objective was to model connectivity between sage-grouse lek sites by applying circuit theory across the annual habitat model. I calculated the correlation between connectivity and habitat use across the annual and nesting habitat selection models to test if greater connectivity resulted in larger and more stable populations independent of habitat. I examined these trends across years of high population as well as years of low population. The structural connectivity of the landscape was not strongly correlated with the relative probability of habitat use across both nesting and annual habitat models (r = 0.3). Increasing connectivity was associated with increasing population sizes at leks and decreasing variability in lek counts; thus signifying that structural connectivity has a positive influence on population abundance and supports greater stability at lek sites. These trends also extended across years of high population as well as years of population declines, therefore indicating the importance of structural connectivity across the full cycle. Overall, my research explicitly integrates across all seasonal habitats supporting a multi-seasonal approach over a single-season approach for identifying priority areas in order to shield sage-grouse from human induced disturbances across the full annual cycle. Furthermore, I found that the structural connectivity of the landscape is beyond a simple summarization of habitat availability; therefore, when prioritizing the landscape and identifying core areas for protection, considering areas of high structural connectivity in addition to good quality habitat would enhance overall conservation outcomes across the full annual cycle.