Role of brown bears (Ursus arctos) in the flow of marine nitrogen into a terrestrial ecosystem (original) (raw)

Abstract

We quantified the amount, spatial distribution, and importance of salmon (Oncorhynchus spp.)-derived nitrogen (N) by brown bears (Ursus arctos) on the Kenai Peninsula, Alaska. We tested and confirmed the hypothesis that the stable isotope signature (δ15N) of N in foliage of white spruce (Picea glauca) was inversely proportional to the distance from salmon-spawning streams (_r_=–0.99 and P<0.05 in two separate watersheds). Locations of radio-collared brown bears, relative to their distance from a stream, were highly correlated with δ15N depletion of foliage across the same gradient (_r_=–0.98 and –0.96 and P<0.05 in the same two separate watersheds). Mean rates of redistribution of salmon-derived N by adult female brown bears were 37.2±2.9 kg/year per bear (range 23.1–56.3), of which 96% (35.7±2.7 kg/year per bear) was excreted in urine, 3% (1.1±0.1 kg/year per bear) was excreted in feces, and <1% (0.3± 0.1 kg/year per bear) was retained in the body. On an area basis, salmon-N redistribution rates were as high as 5.1±0.7 mg/m2 per year per bear within 500 m of the stream but dropped off greatly with increasing distance. We estimated that 15.5–17.8% of the total N in spruce foliage within 500 m of the stream was derived from salmon. Of that, bears had distributed 83–84%. Thus, brown bears can be an important vector of salmon-derived N into riparian ecosystems, but their effects are highly variable spatially and a function of bear density.

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Authors and Affiliations

  1. Alaska Department of Fish and Game, Division of Wildlife Conservation, 333 Raspberry Road, Anchorage, AK 99518, USA e-mail: grant_hilderbrand@fishgame.state.ak.us Tel.: +1-907-2672182, Fax: +1-907-2672433, , , , , , US
    G. V. Hilderbrand & C. C. Schwartz
  2. United States Forest Service, Pacific Northwest Research Station, 2770 Sherwood Lane, Suite 2A, Juneau, AK 99801, USA, , , , , , US
    Thomas A. Hanley
  3. Departments of Natural Resource Sciences and Zoology, Washington State University, Pullman, WA 99164, USA, , , , , , US
    Charles T. Robbins

Authors

  1. G. V. Hilderbrand
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  2. Thomas A. Hanley
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  3. Charles T. Robbins
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  4. C. C. Schwartz
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Received: 11 February 1999 / Accepted: 7 July 1999

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Hilderbrand, G., Hanley, T., Robbins, C. et al. Role of brown bears (Ursus arctos) in the flow of marine nitrogen into a terrestrial ecosystem.Oecologia 121, 546–550 (1999). https://doi.org/10.1007/s004420050961

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