Spatial linkages and stability of Pacific salmon

Migratory animals cross the spatial boundaries of ecosystems and subsidize food web productivity through the input of externally derived resources. However, human activities have altered such spatial linkages through the spread of non-native species. Moreover, the conservation and management of migratory animals is complicated by the broad spatial scales over which they occur. In this thesis, I use field-based studies to examine the spatial linkages created by the Chinook salmon invasion of Patagonia, southern Chile, and apply a metacommunity framework to understand the spatial stability of Pacific salmon. First, I investigate whether Chinook salmon in Patagonia subsidize stream algae through the delivery of marine-derived nutrients. I show that marine-derived nutrients increase algal biomass, indicating that salmon have established a novel linkage between freshwater and marine ecosystems in Patagonia. Next, I use field-based observations and a literature review to examine the trophic interactions that have emerged following this invasion. I describe novel trophic interactions and present evidence that the pathways of salmon nutrient incorporation in North American food webs have functionally re-emerged in South America. Lastly, I use spatio-temporal reconstructions of annual Pacific salmon abundance across the North Pacific Ocean and within northern British Columbia (BC) to test the hypothesis that ecological properties temporally stabilize across larger areas. Across six decades of abundance estimates, I find that the temporal stability of annual salmon abundance is significantly greater in the North Pacific than in northern BC due to the stabilizing effect of spatial asynchrony. I also show that hatchery production of salmon has only a marginal effect on local stability in regions with viable salmon stocks, calling into question the efficacy of hatcheries in stabilizing salmon populations. Overall, this thesis enhances our understanding of the ecological impacts of Patagonian salmon and the effect of salmon management practices on stability while also addressing broader patterns in the trophic interactions that emerge following biological invasions and the emergent properties of ecological systems across spatial scales.