Population Cycles and the Chitty Syndrome

Abstract

Data are presented on the long-term population dynamics of small mammals (1982–2019) and variation in the body weight and length of the bank vole, a dominant species, in southern taiga forests of the Middle Urals. Spontaneous change in the pattern of dynamics observed in our previous study—transition from regular 3-year cycles to noncyclic regime—provided the possibility to estimate the influence of different factors on the Chitty effect (increase in body size at high population numbers) under different regimes. This effect was clearly manifested in the bank vole population with cyclic dynamics: the average body weight and length of the animals were greater at the phases of population growth and peak than at the trough (low) phase, while the same parameters of voles from the noncyclic regime had intermediate values. The body size of animals depends not so much on population density as on factors determining their physiological status (including reproductive status).