Assessing habitat quality for conservation using an integrated occurrence-mortality model.
Abstract
Habitat suitability models are usually produced using species presence or habitat selection, without taking into account the demographic performance of the population considered. These models cannot distinguish between sink and source habitats, causing problems especially for species with low reproductive rates and high susceptibility to low levels of mortality as in the case of the critically endangered Apennine brown bear Ursus arctos marsicanus. We developed a spatial model based on bear presence (2544 locations) and mortality data (37 locations) used as proxies for demographic performance. We integrated an occurrence and a mortality-risk Ecological Niche Factor Analysis model into a final two-dimensional model that can be used to distinguish between attractive sink-like and source-like habitat. Our integrated model indicates that a traditional habitat suitability model can provide misleading management and conservation indications, as 43% of the area suitable for the occurrence model is associated with high mortality risk. Areas of source-like habitat for the Apennine bears (highly elevated areas rich in beech forests, far from roads, and with low human density and cultivated fields) are still present, including outside the currently occupied range. However, attractive sink-like habitat (associated with high levels of pasture, low extent of mountain meadows, low steepness, low elevation, and closeness to secondary and urban roads) are present even inside protected areas. Synthesis and applications. Identifying attractive sink-like habitat is crucial to prevent inappropriate management and to effectively address conservation issues: whereas existing source-like habitats should be preserved to halt habitat loss and degradation, attractive sink-like habitat should be managed to mitigate mortality risks or to decrease their attractiveness. In particular, area-specific management interventions and proactive actions (increased patrolling, road closure, human activity management, threat monitoring, etc.) aimed at reducing human-caused mortality are critical for the Apennine brown bear.