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Fractals, sea-ice landscape and spatial patterns of polar bears

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Abstract:

Periodic landscape transformations can give rise to macroevolutionary changes such as speciation, whereas more constant microevolutionary differences can lead to population differentiation within a species. The most recent major macroevolutionary change occurred 2.5 mya when an abrupt increase in the scale of glacial cycles in the northern hemisphere resulted in the formation of the arctic sea-ice ecosystem. An initial burst of diversity occurred and sometime later polar bears evolved from brown bears as a marine mammal predator of seals living among the sea ice landscape. We tested the hypothesis that the distribution of sea ice creates a spatial patterning in the present groupings of polar bears (i.e. populations). We compared the spatial attributes of sea ice and polar bear characteristics in the Canadian Arctic. The winter and spring seasons, before and during mating, respectively, best described groupings of polar bears based on separate cluster analyses of ice and bears. A relationship between polar bear fractal movement patterns and the fractal dimension of sea ice indicated a possible mechanism linking geography and population structure. Sea ice dominates as a structuring agent and the hierarchical spatial groupings of polar bears within a circumpolar metapopulation related to the fractal pattern of annual sea ice created by the interspersion of Arctic islands. Once a new sea-ice environment formed, directional selection resulted in allopatric speciation whereas stabilizing selection maintains present groupings due to exchanges among populations at the time of breeding.

Keywords: Allopatric speciation; Ursus maritimus; cluster analysis; evolution; metapopulation; movement pathway

Document Type: Research Article

Affiliations: 1: Department of Biology, University of Saskatchewan, 112 Science Place, Saskatoon, SK, S7N 5E2, Canada 2: Department of Resources, Wildlife, & Economic Development, Government of the North-west Territories, PO Box 1870, Iqaluit, NT, X0 A 0H0, Canada 3: Greenland Institute of Natural Resources, Tagensvej 135, DK-2200 Copenhagen N, Denmark

Publication date: November 1, 1998

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