Module 7
Brown Bear Arctic Variants
Brown bears (Ursus arctos) are the polar bear’s sister taxon and occupy Arctic and sub-Arctic coasts where salmon, berries, and forbs substitute for seal. Kamchatka, Kodiak, and ABC Islands subspecies are the largest terrestrial carnivores on Earth. This module covers ecological contrasts and the hybridisation zone.
1. Giant Coastal Subspecies
The Kodiak bear (U. arctos middendorffi) and Kamchatka brown bear(U. arctos beringianus) reach >650 kg on a diet dominated by Pacific salmon runs. Annual salmon pulses deliver hundreds of kg of high-fat fish per bear, funding rapid pre-hibernation deposition of ~50–80 kg of subcutaneous fat. No inland brown bear reaches this body mass; the giant coastal bears are salmon-driven gigantism comparable to polar bears’ seal-driven specialisation.
2. Dietary Contrast
Stable-isotope studies (Hilderbrand 1999) show coastal brown bears derive 60–70% of dietary N from marine sources, vs. >90% for polar bears. Inland grizzlies are <20% meat in many years. The gradient from inland grizzlies to polar bears spans almost the full range of carnivore dietary specialisation, with brown-bear coastal populations in the middle.
Simulation: Subspecies Mass & Diet
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Code will be executed with Python 3 on the server
3. Pizzly/Grolar Hybridisation
Wild hybrids have been documented in the Canadian Arctic since 2006, with at least 17 confirmed individuals as of 2024. The offspring are intermediate in size, cream-coloured, and behaviourally intermediate. Cahill 2013 resolved the deeper history: ABC Islands brown bears carry large polar-bear ancestry fractions (~6–8%) from Pleistocene admixture during glacial refugia isolation.
Climate warming expands the contact zone: brown bears move north as shrub tundra advances, while polar bears are increasingly forced ashore. If hybridisation becomes extensive, introgression could dilute the specialist polar-bear genotype — a controversial conservation question that frames hybridisation as either genetic rescue or loss of identity.
Key References
• Hilderbrand, G. V. et al. (1999). “Role of brown bears in the flow of marine nitrogen into a terrestrial ecosystem.” Oecologia, 121, 546–550.
• Cahill, J. A. et al. (2013). “Genomic evidence for island population conversion resolves conflicting theories of polar bear evolution.” PLOS Genet., 9, e1003345.
• Kelly, B. P. et al. (2010). “The Arctic melting pot.” Nature, 468, 891.
• Van Daele, L. J. et al. (2012). “Kodiak brown bear population trends.” Alaska Dep. Fish Game Tech. Bull.