1. Collapse of Arctic Ground Squirrel Populations in the Yukon Boreal Forest
Charles J. Krebs, Jeffery R. Werner, and Rudy Boonstra
University of British Columbia and University of Toronto, Canada

2. Outline Distribution and natural history Population dynamics
Explanations for recent population collapse
Predictions
Experiments in progress

3. Arctic Ground Squirrel (Urocitellus parryii)
Burrowing herbivore ( g)
Hibernate 8 months of winter
Occupy alpine, forest,
grassland habitats
One litter per year (4-7)
Live in groups of
related females
Density 1-3 per ha

4. Geographical Distribution
Most of geographical
range is in arctic
and alpine tundra

6. Altitudinal Distribution

7. Altitudinal Distribution
ALPINE
Population
collapse
Limited or no recovery
BOREAL
FOREST
High density
Stable
populations
500
meters
1000
2000
2001 -
2014

8. Population Fluctuations - Boreal Forest
Declines driven
by predation

9. Local Dynamics – The Problem # 1
Ground squirrel population changes have been driven by predation as secondary prey
Low snowshoe hare abundance in the past 14 years along with climatic warming have allowed increased shrub growth
Ground squirrels depend on warning calls to alert the colony to predator presence

10. Local Dynamics – The Problem # 2
Hypothesis: increased shrub growth has reduced predator detection and ground squirrels have been driven to local extinction in the boreal forest
Prediction: forest habitats are sinks, and recolonization must come from source areas
Source areas could be alpine populations or small meadows within the forest

11. Landscape Distribution - 2013
A regional effect, not a local effect

12. Decision Tree

13. Dispersal Limitation - Observations
Continuous dispersal within forests and low grasslands of males shown by radio-collaring
No movements of radio-collared squirrels from the alpine down into the boreal forest alpine population are not a source
When we radio-collar juveniles in boreal forest areas in 2013 and 2014, they either move and die or stay and die by predation

14. Decision Tree

15. Decision Tree
continued from above
Experimental
re-introductions ?

16. Possible Allee Effect in Arctic Ground Squirrels
Declines driven
by predation

17. Further Questions
Global warming is increasing winter temperatures and causing freeze-thawing and rainfall during winter
This could produce ice in hibernation burrows, resulting in overwinter mortality
If this is correct, the icing effect should affect both alpine and forest populations

18. Summary
Arctic ground squirrels have disappeared from boreal forest sites where they were formerly very abundant
They appear to be in a predator pit caused by: habitat changes in the forest caused by reduced herbivory and global warming an Allee effect associated with predator warning calls within a colony

19. Thanks for listening