Oecologia

, Volume 121, Issue 4, pp 546–550

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

  • G. V. Hilderbrand
  • Thomas A. Hanley
  • Charles T. Robbins
  • C. C. Schwartz

DOI: 10.1007/s004420050961

Cite this article as:
Hilderbrand, G., Hanley, T., Robbins, C. et al. Oecologia (1999) 121: 546. doi:10.1007/s004420050961

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.

Key words BearNitrogenNutrient flowSalmonSpruce

Copyright information

© Springer-Verlag Berlin Heidelberg 1999

Authors and Affiliations

  • G. V. Hilderbrand
    • 1
  • Thomas A. Hanley
    • 2
  • Charles T. Robbins
    • 3
  • C. C. Schwartz
    • 1
  1. 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: +1-907-2672433US
  2. 2.United States Forest Service, Pacific Northwest Research Station, 2770 Sherwood Lane, Suite 2A, Juneau, AK 99801, USAUS
  3. 3.Departments of Natural Resource Sciences and Zoology, Washington State University, Pullman, WA 99164, USAUS