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A typical stream on the central coast of British Columbia. The photo shows the mouth of Quartcha Creek (52°30 0 52″ N 127°50 0 26″ W) opening into the estuary (Credit: Allison M. Dennert).

A typical stream on the central coast of British Columbia. The photo shows the mouth of Quartcha Creek (52°30 0 52″ N 127°50 0 26″ W) opening into the estuary (Credit: Allison M. Dennert).

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Annual spawning migrations by Pacific salmon can provide substantial subsidies to nutrient‐limited freshwater and riparian ecosystems, which can affect the abundance, diversity, and physical characteristics of plant and animal species in these habitats. Here, we provide the first investigation of how salmon subsidies affect reproductive output in p...

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... and experiences a maritime climate with heavy rainfall-over 3 m annually. We chose streams that span a wide range of salmon v www.esajournals.org 2 November 2020 v Volume 11(11) v Article e03282 spawning densities and experience minimal impacts from recent human activity; streams are accessible only by boat and have had minimal logging activity (Fig. 2). Although multiple types of bedrock exist in our study area, soil properties tend to be similar throughout the region due to the influence of similar climate and vegetative inputs (Heilman and Gass 1974, Kranabetter andBanner 2000). Nutrient cycling in coastal western hemlock forests is primarily confined to the upper soil horizons, ...
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... found a significant positive relationship between the number of fruits produced per shrub and salmon density (Fig. 3A). We also found that stem density and distance from streambank had significant relationships with fruit count-fruit count increased with higher stem density (Fig. 3B) and decreased with distance from the streambank (Appendix S1: Fig. S2). Stem density was the most important predictor of fruit count (RVI = 0.97), followed by distance from streambank (RVI = 0.79), then salmon density (RVI = 0.68). All other variables were not important (RVI < 0.50). However, the effect of salmon density was approximately 1.3 × stronger than stem density and 2 × stronger than distance ...

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... Subsidies fluctuate in amount, quality, timing, and duration, eliciting variable effects on ecosystems (Piovia-Scott et al., 2019;Subalusky & Post, 2019). In one study, larger amounts of spawning salmon significantly increased riparian per-shrub berry production in Canadian streams (Siemens et al., 2020), which potentially affects avian and mammalian consumers (Traveset & Willson, 1998). Another study found that changing the seasonal timing of subsidy addition to plants resulted in a shift from bottom-up effects for herbivores to top-down suppression by predators (Gratton & Denno, 2003). ...
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Although marine subsidies often enrich terrestrial ecosystems, their influence is known to be context-dependent. Additionally, the multitrophic impact of marine subsidies has not been traced through food webs across physically diverse islands. Here, we test predictions about how island characteristics can affect marine enrichment of food web constituents and how nutrients flow through island food webs. To evaluate enrichment and trace marine nutrients across food webs, we used stable isotopes of soil, flora, and fauna (n = 4752 samples) collected from 97 islands in British Columbia, Canada. Island area was the strongest predictor of enrichment across taxa; we found that samples were more 15 N-rich on smaller islands. Enrichment declined with distance from shore but less so on small islands, implying a higher per-unit-area subsidy effect. These area and distance-to-shore effects were taxon-specific, and nearly twice as strong in basal food web groups. We also found that increases in δ 15 N correlated with increases in %N in basal trophic groups, as well as in songbirds, implying biologically relevant uptake of a potentially limiting nutrient. Path analysis demonstrated that subsidies in soil flow through plants and detritivores, and into upper-level consumers. Our results reveal an interplay between island biogeography and marine subsidies in shaping island food webs through bottom-up processes.
... The list of interactors is certainly incomplete due to the limited scope of our field surveys. Other types of interactions that have not yet been studied include responses to salmon-derived nutrients among riparian plants (e.g., Hocking & Reynolds, 2011;Siemens et al., 2020), consumption of juvenile salmon and salmon eggs by forest birds (e.g., Tonra et al., 2016), the transport of salmon-derived nutrients into terrestrial food webs through the emergence of stream insects (e.g., Francis et al., 2006), microbial interactions (discussed below), and bioturbation effects due to disturbance of the streambed (e.g., Moore & Schindler, 2008). Moreover, the prevalence of these interactions likely varies spatially and temporally due to variation in physical and biological characteristics of ecosystems. ...
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In their native range, Pacific salmon (Oncorhynchus spp.) have strong interactions with a multitude of species due to the annual pulse of marine‐derived nutrients that they deliver to streams and forests when they spawn and die. Over the past few decades, Chinook salmon (Oncorhynchus tshawytscha) has established non‐native populations throughout the Patagonia region of southern South America. Here, we provide the first assessment of the pathways through which salmon‐derived nutrients enter stream and forest food webs in Patagonia by surveying multiple streams in southern Chile to identify invertebrate and vertebrate consumers of salmon carcasses and summarizing all documented trophic interactions of Chinook salmon in Patagonia. Blowflies (Calliphoridae) were the dominant colonizer of carcasses in the riparian zone, and midge flies (Chironomidae) were the most common invertebrate on submerged carcasses. Camera trap monitoring in the riparian zone revealed consumption of carcasses or carcass‐associated invertebrates by the insectivorous passerine bird “chucao” (Scelorchilis rubecula), small rodents (black rat Rattus rattus, house mouse Mus musculus, and/or colilargo Oligoryzomys longicaudatus), the South American fox “culpeo” (Lycalopex culpaeus), and the invasive American mink (Neovison vison). A mink was filmed transferring a carcass from stream to streambank, indicating that vertebrate scavenging likely increases the degree to which marine‐derived nutrients enter terrestrial food webs. The native taxa that consume salmon are closely related to species that benefit from salmon consumption in North America, suggesting that the pathways of salmon nutrient incorporation in North American food webs have functionally re‐emerged in South America. Similarly, non‐native trout (Oncorhynchus mykiss and Salmo trutta) and mink consume salmon in Patagonia, and their eco‐evolutionary history of coexistence with salmon could mean that they are preadapted for salmon consumption and could thus be key beneficiaries of this invasion. Expanded monitoring of the abundance and impacts of salmon will be vital for understanding how these novel inputs of marine‐derived nutrients alter Patagonian food webs.