RESULTS
Sine cycle subpopulation growth rates for the Qamanirjuaq subpopulation
(λt) varied from a maximum of 1.196 in the increase
phase to 0.837 in the decline phase (Table 1; Figure 1). All the sine
cycle λ values for the Qamanirjuaq subpopulation were within the maximum
plausible rate of increase (i.e., < 1.2). However, calculated
sine cyclic estimates of the maximum and minimum rates of annual
subpopulation growth were sometimes greater than the maximum
biologically possible intrinsic rate of increase (λmax =
1.363) during the eruption phase for both the Bathurst
(λmax = 1.47; λmin = 0.68) and George
River (λmax = 2.85; λmin = 0.35)
subpopulations (Table 1; Figure 2; Figure 3).
Barren-ground caribou subpopulation numbers (Nt) closely
tracked carrying capacity (Kt) for all three
subpopulations (Table 1; Figure 1; Figure 2; Figure 3; Figure 4). Mean
cycle lag times (years for Nt →Kt) at
observed λt (Nt+1/Nt)
for the Qamanirjuaq, Bathurst, and George River subpopulations were
2.898 (SE = 0.008), 2.661 (SE = 0.103), and 2.430 (SE = 0.121)
respectively (Table 2; Figure 4). Kruskal-Wallis pairwise comparison of
the observed mean Nt →Kt lag times of
each subpopulation over one complete cycle demonstrated that the mean
lag time (intrinsic + immigration) for the George River subpopulation
was significantly different from the Qamanirjuaq (p = 0.018), but not
significantly different from the Bathurst (p = 0.838) subpopulation
(Table 3). The difference in mean lag times between the Qamanirjuaq and
Bathurst subpopulation was also not significant (p = 0.414) (Table 3).
When the period of eruption years was excluded from the comparison of
mean lag time values (i.e., only intrinsic lag times included) there
were no significant differences in the projected lag time values between
any of the three subpopulations (p = 0.249) (Table 3). When pairwise
comparisons were restricted to only the eruption period the mean lag
time for the George River subpopulation was significantly different from
the Qamanirjuaq (p = 0.013) but not significantly different from the
Bathurst (p = 0.690). The difference in mean lag time between the
Qamanirjuaq and Bathurst subpopulations was also not significant (p =
0.221) (Table 3).
Kruskal-Wallis pairwise comparison of mean population growth rates
resulted in no significant difference between subpopulations for one
complete cycle (p = 0.958) or for one complete cycle excluding eruption
years (p = 0.249) (Table 4). When only eruption years were considered
separately, the mean population growth rate for the George River
subpopulation was significantly different than mean population growth
rate for the Qamanirjuaq (p = 0.001) but not significantly different
from the Bathurst mean population growth rate (p = 0.427). The
difference in mean population growth rate between the Qamanirjuaq and
Bathurst subpopulations was also not significant (p = 0.070) (Table 4).
Subpopulation annual growth rates during the eruption phase of the sine
cycle sometimes exceeded the biologically possible and biologically
plausible intrinsic growth rates for barren-ground caribou in both the
Bathurst and George River subpopulations (Figure 5). However, the
Qamanirjuaq subpopulation growth rates were entirely within the
plausible intrinsic value (λplausible = 1.2) (Figure 5).
The additional annual increase observed in the George River and Bathurst
eruption phase was attributed to extrinsic growth (i.e., immigration)
(Figure 6). Immigration rates for the Bathurst subpopulation initially
increased, peaked, and then declined (Figure. 6). Immigration rates for
the George River subpopulation were highest initially then declined
throughout the eruption phase (Figure 6).
K-means cluster analysis identified three distinct clusters of lag time
values and population growth rate values for the eruption years of each
subpopulation cycle. Clusters were characterized as: 1) short N→K time
lags and high lambda values, 2) intermediate N→K time lags and
intermediate lambda values, and 3) long N→K time lags and low lambda
values (Figure 7). Cluster 1 was exclusively associated with the George
River subpopulation (Figure 7). Cluster 2 was mainly comprised of
Bathurst records but also contained George River and Qamanirjuaq
records. Cluster 3 was predominantly associated with the Qamanirjuaq
subpopulation.
Population growth rate, carrying capacity, and lag time were all
correlated (p≤0.05) for each of the three subpopulations (Table 5).