25.2 Lemming Model Equations
N1(t) ¼ N1(t À dt) + (ΔN1) * dt
INIT N1 ¼ 1 {Individuals per Unit Area}
INFLOWS:
ΔN1 ¼ IF N1>0 THEN N1 * (A1-(B1-C1)*N2-C1*(N1+N2)) ELSE 0 {Individuals
per Unit Area per Time Period}
N2(t) ¼ N2(t À dt) + (ΔN2) * dt
INIT N2 ¼ 1 {Individuals per Unit Area}
INFLOWS:
ΔN2 ¼ IF N2>0 THEN N2 * (ÀA2+B2 * N1) ELSE 0 {Individuals per Unit Area per
Time Period}
A1 ¼ .9 {1/Time Period}
A2 ¼ .5 {1/Time Period}
B1 ¼ .9 {1/Individuals per Unit Area per Time Period}
B2 ¼ .2 {1/Individuals per Unit Area per Time Period}
C1 ¼ .0043 {1/Individuals per Unit Area per Time Period}
References
1. Decker H (1975) A simple mathematical model of rodent population cycles. J Math Biol
2(1):57–67
2. Myers HJH, Krebs CJ (1971) Genetic, behavioral and reproductive attributes of dispersing field
voles Microtus pennsylvanicus and Microtus ochragaster. Ecol Monogr 41(1):53–78
Fig. 25.3
References
209