The use of focal species for conservation: A test of their ability to measure ecological resilience in dynamic systems
Our ability to manage ecosystems toward long-term resilience is continually challenged by our understanding of ecology and ecosystem dynamics, the effective application of that knowledge to management actions, and the increasing pace of change in ecological conditions and their drivers. Biodiversity is essential to resilient ecosystems, but our ability to measure, monitoring and conserve biodiversity continues to fall short of the demand. Some combination of coarse and fine filter approaches have strong conceptual appeal, however evidence of their success is scant. We explore applications of the focal species concept – species that represent ecological conditions, which in turn support biological diversity – to bird occupancy data to evaluate how robust this new approach to representation and measurement is to the long-standing challenges of representing complex and temporally dynamic systems. Specifically, we use a multi-species hierarchical occurrence model to identify possible focal species in the Lake Tahoe Basin. Using this approach we model the probability of occurrence of 64 avian species as a function of specific abiotic and habitat covariates related to forest structure. With a dataset collected 10 years after the initial effort, we test whether species habitat associations change over time in general, and whether focal species selected would help us manage for ecological resilience.
Our results indicate that few species were strongly associated with local elements of forest structure, rather physical factors such as precipitation, elevation, and urban development had the strongest influence on occurrence. We did find that over the 10 year timeframe there was consistency in response for most species that were strongly associated with specific habitat conditions. Co-occurrence patterns of species were not entirely consistent with species habitat associations, indicating that additional information on biodiversity and ecosystem resilience can be gleaned by tracking changes in composition and strength of co-occurrence within and among suites of focal species. Environmental drivers, most notably climate change and urbanization, are disassembling communities through the unique responses of species to environmental change. These dynamics will require managers and practitioners to stay nimble in their thinking about what to measure, how to measure it, and how to interpret changes in representative measures. Application of focal species approach to measuring and monitoring ecosystem resilience could be robust to changing relationships with over time with attention to the underlying assumptions behind their selection, data collection, and interpretation.