Do bears facilitate transfer of salmon resources to aquatic macroinvertebrates?

Winder, Monika; Schindler, Daniel E.; Moore, Jonathan W.; Johnson, Susan P.; Palen, Wendy J.

doi:10.1139/f05-136

Cited by 34 publications

(23 citation statements)

References 37 publications

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“…In the water, they would have been decomposed by scavenging aquatic insects (Minakawa and Gara , Winder et al. ) and bacteria. Dissolved nutrients may leach into hyporheic flows and be acquired by riparian trees (O'Keefe and Edwards ).…”

Section: Discussionmentioning

confidence: 99%

A multidecade experiment shows that fertilization by salmon carcasses enhanced tree growth in the riparian zone

Quinn

Helfield

Austin

et al. 2018

Ecology

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As they return to spawn and die in their natal streams, anadromous, semelparous fishes such as Pacific salmon import marine‐derived nutrients to otherwise nutrient‐poor freshwater and riparian ecosystems. Diverse organisms exploit this resource, and previous studies have indicated that riparian tree growth may be enhanced by such marine‐derived nutrients. However, these studies were largely inferential and did not account for all factors affecting tree growth. As an experimental test of the contribution of carcasses to tree growth, for 20 yr, we systematically deposited all sockeye salmon (Oncorhynchus nerka) carcasses (217,055 individual salmon) in the riparian zone on one bank of a 2‐km‐long stream in southwestern Alaska, reducing carcass accumulation on one bank and enhancing it on the other. After accounting for partial consumption and movement of carcasses by brown bears (Ursus arctos) and variation in salmon abundance and body size, we estimated that 267,620 kg of salmon were deposited on the enhanced bank and 45,200 kg on the depleted bank over the 20 yr, for a 5.9‐fold difference in total mass. In 2016, we sampled needles of 84 white spruce trees (Picea glauca) the dominant riparian tree species, for foliar nitrogen (N) content and stable isotope ratios (δ15N), and took core samples for annual growth increments. Stable isotope analysis indicated that marine‐derived N was incorporated into the new growth of the trees on the enhanced bank. Analysis of tree cores indicated that in the two decades prior to our enhancement experiment, trees on the south‐facing (subsequently the depleted) bank grew faster than those on the north‐facing (later enhanced) bank. This difference was reduced significantly during the two decades of fertilization, indicating an effect of the carcass transfer experiment against the background of other factors affecting tree growth.

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Section: Discussionmentioning

confidence: 99%

A multidecade experiment shows that fertilization by salmon carcasses enhanced tree growth in the riparian zone

Quinn

Helfield

Austin

et al. 2018

Ecology

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“…with the highest energy content (large individuals that have spent the fewest number of days on the spawning grounds), which increases the likelihood of transport of those salmon into the riparian zone (Gende et al, ; Hocking & Reimchen, ). Bear‐killed salmon that are left in the river are preferentially colonized by caddisfly larvae compared to senesced carcasses, possibly due to their higher energetic content, improved accessibility, or extended temporal availability (Winder et al, ). This prey selection is also mediated by stream habitat structure, and in complex habitats where preferred salmon are difficult to catch, bears selectively kill older, more senesced individuals (Gende et al, ).…”

Section: Recipient Ecosystem – Consumer Characteristicsmentioning

confidence: 99%

Context dependency of animal resource subsidies

2018

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The transport of resource subsidies by animals has been documented across a range of species and ecosystems. Although many of these studies have shown that animal resource subsidies can have significant effects on nutrient cycling, ecosystem productivity, and food‐web structure, there is a great deal of variability in the occurrence and strength of these effects. Here we propose a conceptual framework for understanding the context dependency of animal resource subsidies, and for developing and testing predictions about the effects of animal subsidies over space and time. We propose a general framework, in which abiotic characteristics and animal vector characteristics from the donor ecosystem interact to determine the quantity, quality, timing, and duration (QQTD) of an animal input. The animal input is translated through the lens of recipient ecosystem characteristics, which include both abiotic and consumer characteristics, to yield the QQTD of the subsidy. The translated subsidy influences recipient ecosystem dynamics through effects on both trophic structure and ecosystem function, which may both influence the recipient ecosystem's response to further inputs and feed back to influence the donor ecosystem. We present a review of research on animal resource subsidies across ecosystem boundaries, placed within the context of this framework, and we discuss how the QQTD of resource subsidies can influence trophic structure and ecosystem function in recipient ecosystems. We explore the importance of understanding context dependency of animal resource subsidies in increasingly altered ecosystems, in which the characteristics of both animal vectors and donor and recipient ecosystems may be changing rapidly. Finally, we make recommendations for future research on animal resource subsidies, and resource subsidies in general, that will increase our understanding and predictive capacity about their ecosystem effects.

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“…This region is also populated by brown bears (Ursus arctos). Long-term surveys of salmon abundance and bear predation in the Wood River System has shown that annual predation rates by bears on sockeye salmon range from 5 to 82% of spawning individuals (Winder et al 2005). We studied riparian habitats of six sites on four streams to investigate the effect of salmon and bears on soil N cycling ( Fig.…”

Section: Site Descriptionmentioning

confidence: 99%

Large predators and biogeochemical hotspots: brown bear (Ursus arctos) predation on salmon alters nitrogen cycling in riparian soils

Holtgrieve

Schindler

Jewett

2009

Ecological Research

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Two important themes in ecology include the understanding of how interactions among species control ecosystem processes, and how habitats can be connected through transfers of nutrients and energy by mobile organisms. An impressive example of both is the large influx of nutrients and organic matter that anadromous salmon supply to inland aquatic and terrestrial ecosystems and the role of predation by brown bears (Ursus arctos) in transferring these marine-derived nutrients (MDN) from freshwater to riparian habitats. In spite of the recognition that salmon-bear interactions likely play an important role in controlling the flux of MDN from aquatic to riparian habitats, few studies have linked bear predation on salmon to processes such as nitrogen (N) or carbon (C) cycling. We combine landscape-level survey data and a replicated bear-exclosure experiment to test how bear foraging on salmon affects nitrous oxide (N 2 O) flux, carbon dioxide (CO 2 ) flux, and nutrient concentrations of riparian soils. Our results show that bears feeding on salmon increased soil ammonium (NH 4 + ) concentrations three-fold and N 2 O flux by 32-fold. Soil CO 2 flux, nitrate (NO 3 À ), and N transformation differences were negligible in areas where bears fed on salmon. Reference areas without concentrated bear activity showed no detectable change in soil N cycling after the arrival of salmon to streams. Exclosure experiments showed that bear effects on soil nutrient cycles were transient, and soil N processing returned to background conditions within 1 year after bears were removed from the system. These results suggest that recipient ecosystems do not show uniform responses to MDN inputs and highlight the importance of large mobile consumers in generating landscape heterogeneity in nutrient cycles.

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Do bears facilitate transfer of salmon resources to aquatic macroinvertebrates?

Cited by 34 publications

References 37 publications

A multidecade experiment shows that fertilization by salmon carcasses enhanced tree growth in the riparian zone

A multidecade experiment shows that fertilization by salmon carcasses enhanced tree growth in the riparian zone

Context dependency of animal resource subsidies

Large predators and biogeochemical hotspots: brown bear (Ursus arctos) predation on salmon alters nitrogen cycling in riparian soils

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