The Spatial Structure of Polar Bear PopulationsThe Spatial Structure of Polar Bear Populations

From Genes to Distribution of the SpeciesFrom Genes to Distribution of the Species

Dr. François Messier

Outline

• Introduction• Individual movements• Influences on individual movements• Population delineation based on telemetry• Genetic basis of demographic units• Concluding remarks

What is a ‘Population’?

A biological unit at the level of ecological integration where it is meaningful to speak of birth rate, death rate, sex ratios and age structures in describing properties or parameters of the unit.

L.C. Cole (1957)

Defining Populations

• Defining populations is of major practical importance to population ecologists– Meeting assumptions of demographic models– Managing populations for harvest– Identifying units important for conservation

(e.g., red list assessment)

Polar Bears

• Management of polar bears requires accurate definition of populations– Harvested species– Occur in relatively small numbers (~25,000 animals

world-wide) over a large (circumpolar) area– Conservation

• Bears in some regions not at risk• Bears in other areas severely depleted• Climate change and pollutants are likely to affect bears in

a spatially heterogeneous manner

Individual Movements

• Based on satellite radio-collared females• Home ranges (n = 93) show considerable

variation– Mean 125,000 km2

– Range 940540,700 km2

– Standard deviation 43,900 km2

Ferguson, S.H., M.K. Taylor, E. Born, A. Rosing-Asvid, and F. Messier. 1999. Ecology Letters 5: 311–318.

Ferguson, S.H., M.K. Taylor, E. Born, A. Rosing-Asvid, and F. Messier. 1999. Ecology Letters 5: 311–318.

14 females

Ferguson, S.H., M.K. Taylor, A. Rosing-Asvid, E. Born, and F. Messier. 2000. Journal of Mammalogy 81: 1118–1127.

Ferguson, S.H., M.K. Taylor, A. Rosing-Asvid, E. Born, and F. Messier. 2000. Journal of Mammalogy 81: 1118–1127.

FIG. 2.—Seasonal timing of use of maternity dens by female polar bears according to latitude, 1991–1997. Median den entry date was 15 September and median exit date was 20 March. Each thin line represents a bear that was tracked for 1 year and entered a maternity den (thick horizontal line). Y-axis is sorted according to latitude.

Ferguson, S.H., M.K. Taylor, A. Rosing-Asvid, E. Born, and F. Messier. 2000. Journal of Mammalogy 81: 1118–1127.

FIG. 3.—Seasonal timing of use of autumn (light shading) and winter (dark shading) shelter dens by female polar bears (thick horizontal bars) according to latitude, 1991–1997. For use of shelter dens in autumn, median entry date was 11 September, median exit date was 2 November, and entry was before 1 December. For use of shelter dens in winter, median entry date was 24 December, median exit date was 2 March, and entry was after 1 December. Each thin line represents a bear that was tracked for 1 year and excludes females that used maternity dens. Y-axis is sorted according to latitude.

Defining Populations Based on Movements

• Determined centroids of movements for collared polar bears

• Grouped bears according to hierarchical cluster analysis

• Defined cumulative ‘home range’ of bears assigned to different clusters

Defining Populations Based on Genetics

• Tissue samples (ear plugs) yield data on genetic differences between bears

Concluding Remarks

• Polar bears are arranged into relatively distinct populations in North America

• Within each population area, most polar bears adopt a ‘roving’ pattern of movement– Influenced by dynamics of sea ice– Influenced by latitude (constraints posed by denning)

• Polar bears use extremely large ranges with high overlap among individuals

• Good match of the spatial structure of individuals at the ecological and genetic levels

Acknowledgements

• Seeglook Akeeagok, Steve Amstrup, Dennis Andriashek, William Barbour, Erik Born, Wendy Calvert, Dean Cluff, Andy Derocher, Gerald Garner, Steve Ferguson, Jeff Laake, Philip McLoughlin, Marty Obbard, David Paetkau, Amanda Plante, Aqqalu Rosing-Asvid, Ian Stirling, Curtis Strobeck, Mitch Taylor, Oysten Wiig Bonita Wong, plus many others!