Northwest Fisheries Science Center

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Document Type: Journal Article
Center: NWFSC
Document ID: 9070
Title: Phenological synchronization disrupts a keystone trophic interaction
Author: W. W. Deacy, J. B. Armstrong, W. B. Leacock, C. T. Robbins, D. D. Gustine, E. J. Ward, J. A. Erlenbach, J. A. Stanford
Publication Year: 2017
Journal: Proceedings of the National Academy of Sciences
Keywords: phenology,salmon,brown bear,mismatch,

Climate change is altering the seasonal timing of life-cycle events in organisms across the planet1, but the magnitude of change often varies among taxa2. Unequal phenological responses can cause the temporal relationships among species to change, potentially altering the strength of interaction. A large body of work has explored what happens when co-evolved species shift out of sync3,4, but virtually no studies have documented the effects of climate-induced synchronization, which could remove temporal barriers between species and create novel interactions.  We explored how a keystone predator, the Kodiak brown bear (Ursus arctos middendorffi), responded to asymmetric phenological shifts between its primary trophic resources, sockeye salmon (Oncorhynchus nerka) and red elderberry (Sambucus racemosa). In years with anomalously high spring air temperatures, elderberry fruited several weeks earlier in the summer and became available during the period when salmon spawned in streams. In years with synchronized resource phenologies, bears left salmon spawning streams, where they typically kill 25-75% of the salmon run5, to forage on berries on adjacent hillsides. Scat surveys corroborated that bears switched from salmon to elderberries, which are less energy dense than salmon, but likely provided a mix of macronutrients that results in higher rates of weight gain. This prey switching behavior attenuated one of the most iconic predator-prey interactions in North America and certainly altered the many ecological functions and services that result from bears foraging on salmon6. We provide one of the first examples of how climate-induced shifts in resource phenology can restructure food webs through a mechanism other than trophic mismatch. The current emphasis on singular consumer-resource interactions fails to capture how climate-altered phenologies are rescheduling resource availability and in turn altering how energy flows through ecosystems.

Theme: Ecosystem approach to improve management of marine resources
Foci: Understand how climate influences ecosystem variability.
Assess ecosystem status and trends.