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North American barren-ground caribou cycles are driven by logistic trophic dynamics
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  • Eric Bongelli,
  • Martha Dowsley,
  • Dean Cluff,
  • Mitch Campbell,
  • Mitchell Taylor
Eric Bongelli
Lakehead University Faculty of Science and Environmental Studies

Corresponding Author:[email protected]

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Martha Dowsley
Lakehead University
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Dean Cluff
Government of the Northwest Territories
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Mitch Campbell
Government of Nunavut
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Mitchell Taylor
Lakehead University
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We used the Qamanirjuaq, Bathurst, and George River barren-ground caribou sine cycles to project numbers (Nt), calculate subpopulation annual growth rates (λt) and calculate logistic carrying capacity (Kt). Maximum annual growth rate was 1.196 and maximum annual rate of decline was 0.836 for the harvested Qamanirjuaq subpopulation sine cycle. However, the maximum annual subpopulation growth rates for both the harvested Bathurst and George River subpopulation sine cycles were greater than the biologically possible maximum intrinsic rate of increase during the eruption phase. Subpopulation numbers for Qamanirjuaq, Bathurst and George River barren-ground caribou subpopulations all closely tracked carrying capacity for one complete cycle with lag times between Nt and Kt ranging from < 1-year to approximately 5-years. The short lag times observed indicates that Qamanirjuaq, Bathurst and George River barren-ground caribou subpopulations closely track their range condition. Range condition drives barren-ground caribou subpopulation cycles, but range condition also cycles; presumably because annual barren-ground caribou grazing rates are proportional to barren-ground caribou numbers and eventually exceed range annual growth rates. Immigration from adjacent subpopulations plays a role in the initiation and acceleration of the eruption period in some subpopulations, but not all of them. Numerical synchrony and asynchrony with adjacent subpopulation cycles can affect the timing of the eruption phase through mediation of immigration. Once subpopulation range has recovered, the rapid recovery of subpopulation numbers suggest that subpopulations are not restricted by other factors. The regularity and symmetry of both the increase and decline phases of these cycles suggests that the barren-ground caribou cycle is both stable and resilient. Continuation of barren-ground caribou cycles at historical levels is likely if habitat conservation measures are adopted so that annual migration patterns are not disrupted, summer and winter range remain undisturbed and common-sense harvest management policies are adopted when caribou are at low numbers.