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

Periodic landscape transformations can give rise to macroevolutionary chang es such as speciation, whereas more constant microevolutionary differences can lead to population differentiation within a species. The most recent ma jor macroevolutionary change occurred 2.5 mya when an abrupt increase in th e scale of glacial cycles in the northern hemisphere resulted in the format ion 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 hypoth esis that the distribution of sea ice creates a spatial patterning in the p resent groupings of polar bears (i.e. populations). We compared the spatial attributes of sea ice and polar bear characteristics in the Canadian Arcti c. The winter and spring seasons, before and during mating, respectively, b est described groupings of polar bears based on separate cluster analyses o f ice and bears. A relationship between polar bear fractal movement pattern s and the fractal dimension of sea ice indicated a possible mechanism linki ng geography and population structure. Sea ice dominates as a structuring a gent and the hierarchical spatial groupings of polar bears within a circump olar metapopulation related to the fractal pattern of annual sea ice create d by the interspersion of Arctic islands. Once a new sea-ice environment fo rmed, directional selection resulted in allopatric speciation whereas stabi lizing selection maintains present groupings due to exchanges among populat ions at the time of breeding.