COS 33-5 - Pacific salmon and the spatial stability of ecological properties

Background/Question/Methods

The temporal stability of ecosystem functioning (i.e., its invariability over time) sets the inter-annual reliability of ecosystem services, making the drivers of stability of interest to ecologists and resource managers alike. It has recently been posited that aggregate ecological properties (e.g., community biomass, metapopulation abundance) stabilize across increasingly large spatial scales, with larger areas incorporating more asynchrony among spatial patches and thus more stability. We tested this hypothesis by quantifying the temporal stability of Pacific salmon (Oncorhynchus spp.) abundance over the past sixty years at two spatial scales: the North Pacific Ocean (i.e., the entire native range of Pacific salmon) and the northern coast of British Columbia (BC), Canada. Within both spatial scales, we partitioned temporal variation in the regional stability of annual salmon abundance among local stability (i.e., average stability of individual patches) and spatial asynchrony (i.e., dissimilarity of temporal fluctuations in abundance among patches). Furthermore, at the North Pacific scale, we quantified the degree to which artificial hatchery production of salmon stabilizes salmon abundance.

Results/Conclusions

We found that the stability of annual salmon abundance was significantly higher in the North Pacific than in northern BC, with asynchronous dynamics among patches increasing the regional stability of annual salmon abundance by an average of 170% in the North Pacific and 63% in northern BC. Indeed, spatial asynchrony was a stronger driver of regional stability in the North Pacific than in northern BC, supporting the hypothesis that ecological properties stabilize across increasingly large spatial scales. Temporal variation in regional stability was primarily caused by pink salmon (O. gorbuscha) shifting between periods of high and low spatial asynchrony. At the North Pacific scale, hatchery production of salmon had only a marginal effect on local stability in all patches except Japan, calling into question the efficacy of hatchery programs in stabilizing salmon abundance. These results speak to the emergent properties of meta-ecosystems and highlight the importance of spatial portfolios in the temporal maintenance of ecosystem services.