Roles of Self Regulatory Mechanisms in Cyclic Populations of Clethrionomys with Special Reference to C. Glareolus: A Hypothesis

Abstract

Self-regulating mechanisms in Clethrionomys spp. were integrated to illustrate the roles which they may play in a population cycle. The following 5 features were considered: spacing behavior and breeding territories, dominance and hierarchy; the size of the overwintered population in relation to the number of breeding territories which appeared to influence body size of the overwintered individuals, the date of the initiation of breeding, the breeding strategy during summer and the survival pattern of the following and overwintering population; suppression of maturation of young individuals; the potential functions and survival patterns of the 3 cohorts of the year, K1-K3. A 4-yr cycle is presented illustrating how interplay of these 5 points can generate the events leading to a population peak and decline. Sparse populations are associated with a surplus of breeding territories thus leading to minimal social conflict, a long breeding season and maturation of the young born early in the season. The progressive increase in numbers during the following 2-3 yr, which is associated with good winter survival, leads to a shortage of breeding territories, increased social strife, delayed breeding and reduced juvenile maturation and survival. Type M and G population declines (crash and gradual decrease, respectively), appear to be related to the lack or presence of K3, respectively, during a peak year. The interaction between predation and self-regulating mechanisms is interpreted as modifying the rate and extent of the decline and the subsequent building up of rodent numbers.