Figure 2. The Bathurst subpopulation tracked carrying capacity (K)
throughout its population cycle. Maximum and minimum rates of annual
(intrinsic + immigration) population growth (λmax =
1.469; λmin = 0.68) were greater than the biological
maximum annual population growth rate (λmax = 1.363;
Heard, 1980) during the eruption phase. The eruption period (λ
> 1.0 and increasing over consecutive years or λ
>1.20) last for approximately 9-years. When
λt values were ≥ 1.2 we limited them to 1.2 for
calculation of the associated Verhulst (1838) carrying capacity
(Kt) because the Verhulst logistic equation is specific
for intrinsic λ only (no immigration). We choose λ ≥ 1.2 as the
threshold because natural populations experience both natural and
harvest mortality and not every reproductive age female would produce
viable offspring each year. Nt closely tracks
Kt throughout the cycle with the maximum lag time over
one complete cycle (1978-2020) being 4.238-years.