Abstract:
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 during the eruption phase 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 (mean lag times were 2.898, 2.661, and 2.430 years respectively). The short lag times observed indicates that Qamanirjuaq, Bathurst, and George River barren-ground caribou subpopulations closely track their range condition, and that grazing impacts begin to reduce intrinsic subpopulation growth rates about midway into the increase portion of the cycle. 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. Barren-ground caribou numbers and their carrying capacity (Kt) sine cycle because state variables in this relatively simple two-level trophic relationship are mutually dependent. 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. However 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.
Key Words: barren-ground caribou, carrying capacity, cyclic species, demography, density effects, management, population cycles, resilience, sine cycle
1 Faculty of Science and Environmental Studies. Department of Geography and Environment, Lakehead University. 955, Oliver Road, Thunder Bay, ON, Canada P7B 5E1. | KBM Resources Group, 349 Mooney Avenue, Thunder Bay, Canada ON, P7B 5L5. (esbongel@lakeheadu.ca)
2 Faculty of Science and Environmental Studies. Department of Geography and Environment, Lakehead University. 955, Oliver Road, Thunder Bay, ON, P7B 5E1
3 Regional Biologist North Slave Region. Department of Environment and Natural Resources, Government of Northwest Territories. 3803 Bretzlaff Drive, Yellowknife, NT. X1A 2P9
4 Regional Wildlife Biologist Kivalliq Region. Wildlife Research Division, Department of Environment, Government of Nunavut. PO Box 120, Arviat, NU, X0C 0E0.