Assessing spatial variability and efficacy of surrogate species at an ecosystem scale

Preserving biodiversity is a central goal of conservation, but, in practice, monitoring biodiversity often involves assessing population trends for one or a handful of species that are presumed proxies for biodiversity. Despite the popularity of surrogate species strategies, the links between biodiversity and surrogate species are rarely tested, especially across the broad spatial scales at which they are applied. We quantitatively evaluated a prominent surrogate species strategy across 25,000 km² of California's Sierra Nevada, an ecosystem undergoing substantial forest loss due to changing fire regimes and climate. We used passive acoustic monitoring and multispecies occupancy models to quantify pairwise co-occurrence among 6 indicator species and much of the avian community (63 species). We found that 95% of the sampled avian community had a positive association with at least one indicator species and that latitude played an important role in shaping co-occurrence for many species. Our work provides an important test of a long-standing conservation tool, suggests that a well-chosen suite of surrogate species can represent the occurrence patterns of a large portion of the rest of the community, and demonstrates the importance of explicitly considering the spatial scale over which surrogate species are effective.