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User:Missypooh7664/Grizzly Bears and Their Effects on Ecosystems

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Grizzly Bears and Their Effects on Ecosystems

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     Grizzly bears play an important role in the ecosystems they inhabit.

     One such relationship is a mutualistic relationship with fleshy-fruit bearing plants.  After the grizzly consumes the fruit, the seeds are dispersed and excerted in a germinable condition.  Some studies have shown that germination sucess is indeed increased as a result of seeds being deposited along with nutrients in feces [1]  This makes the grizzly bear an important seed distributor in their habitat [2]
     While foraging for tree roots, plant bulbs, or ground squirrels, bears stir up the soil.  This process not only helps grizzlies access their food, but it also increases species richness in alpine ecosystems [3].  An area that contains both bears digs and undisturbed land has greater plant diversity than an area that contains just undisturbed land [4].  Along with increasing species richness, soil disturbance causes nitrogen to be dug up from lower soil layers, and makes nitrogen more readily available in the environment [5]. An area that has been dug by the grizzly bear has significantly more nitrogen than an undisturbed area.

     Nitrogen cycling is not only facilitated by grizzlies digging for food, it is also accomplished via their habit of carrying salmon carcasses into surrounding forests [6]. It has been found that Spruce tree (Picea glauca) foliage within 500m of the stream where the salmon have been obtained, contains nitrogen originating from salmon the bears have preyed on [7]. These nitrogen influxes to the forest are directly related to the presence of grizzly bears and salmon [8]. Being a top carnivore, other communities would be afftected by grizzly bear removal.  An experiment in Grand Teton National Park, Wyoming, USA, showed that removal of wolves and grizzly bears caused populations of their herbivorous prey increased [9]. This in turn changed the structure and density of plants in the area, which decreased the population sizes of migratory birds [10]. This provides evidence that grizzly bears represent a keystone predator, having a major influence on the entire ecosytem they inhabit.

References

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  1. ^ Meyer, G. & Witmer, M. (1998). Influence of Seed Processing by Frugivorous Birds on Germination Success of Three North American Shrubs. Am. Midl. Nat. 140: 129-139.
  2. ^ Willson, M., Gende, S. (2004). Seed Dispersal by Brown Bears, Ursus arctos, in Southeastern Alaska. Canadian Field-Naturalist, 118(4), 499-503.
  3. ^ Doak, D. & Loso, M. (2003). Effects of Grizzly Bear Digging on Alpine Plant Community Structure. ARCTIC ANTARCTIC AND ALPINE RESEARCH, 35(4), 499-503.
  4. ^ Doak, D. & Loso, M. (2003). Effects of Grizzly Bear Digging on Alpine Plant Community Structure. ARCTIC ANTARCTIC AND ALPINE RESEARCH, 35(4), 499-503.
  5. ^ Tardiff, S., & Stanford, J. (1998). Grizzly Bear Digging: Effects on Subalpine Meadow Plants in Relation to Mineral Nitrogen Availabilty. Ecology, 79(7), 2219-2228.
  6. ^ Quinn, T., Carlson, S., Gende., & Rich, H. (2009). Transportation of Pacific Salmon Carcasses from Streams to Riparian Forests by Bears. CANADIAN JOURNAL OF ZOOLOGY-REVUE CANADIENNE DE ZOOLOGY, 87(3), 195-203.
  7. ^ Hilderbrand, G., Hanley, T., Robbins, C. & Schwartz, C. (1999). Role of Brown Bears (Ursus arctos) in the Flow of Marine Nitrogen into a Terrestrial Ecosystem. Oecologia, 121(4), 546-550.
  8. ^ Helfield, J. & Naiman, R. (2006). Keystone Interactions: Salmon and Bear in Ripparian Forests of Alaska. Ecosystems, 9(2), 167-180.
  9. ^ Berger, J., Stacey, P., Bellis, L. & Johnson, M. (2001). A Mammalian Predator-Prey Imbalance: Grizzly Bear and Wolf Extinction Affect Avian Neo-Tropical Migrants. Ecological Applications, 11(4), 947-960.
  10. ^ Berger, J., Stacey, P., Bellis, L. & Johnson, M. (2001). A Mammalian Predator-Prey Imbalance: Grizzly Bear and Wolf Extinction Affect Avian Neo-Tropical Migrants. Ecological Applications, 11(4), 947-960.
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