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.