Fluctuations in an island bank vole population in the light of the study on its organization

Abstract

A lon g-term study on the dem ography of an island population of the bank vole, C lethrionom ys glareolus (Schreber, 1780), provided a deeper insight into the mechanisms underlying num ber fluctuations, also reproduction rate and survival of different components of the pop ulation structure. Am ong these processes only reproduction was regulated, which stabilized population num bers during the breeding season. Survival, being subject to random factors (except for par ticularly low population densities), w as a destabilizing process leading to num ber fluctuations. Based on the described relationships between reproduction and survival, on the one hand, and population num bers, on the other, a stepwise sim ulation w as run for 55 years. The results of this empirical model were compared w ith field results. It has been pointed out that random changes in temperature and food conditions in spring generate a 2.6-year cycle, w hile 11-year cycle in these con ditions generates an 11-year cycle of the bank vole num bers. The results are discussed against the background of recent concepts con cerning population demography. It has been shown that num ber fluctuations should not always be identified w ith num ber regulation of the entire population, and that they need not be subject to densitydependent processes.[Institute of Ecology P A S , Dziekanów . 05-092 Łom ianki, Poland]

Sex ratio in an island population of Clethrionomys glareolus (Schreber, 1780)

“…As was shown earlier (Bujalska, 1970(Bujalska, , 1973(Bujalska, , 1985) the number of mature females is relatively stable and independent of population numbers from June to September due to a tendency toward territoriality.…”

“…The sex ratio in April deserves particular attention because the population then consists of overwintered voles only, and their number is highly correlated with food availability (Bujalska, 1985). The April sex ratio seems to be independent of the sex ratio in the previous October (Table 1).…”

Multi-annual fluctuations in the size of a population of the bank vole in European part of the Soviet Union

“…In a plastic species such as the bank vole (Clethrionomys glareolus) pop ulation dynamics vary greatly throughout its vast geographical range. This can be seen clearly by a comparison of the "European bank vole" (Bashenina, 1981) and the studies done by other authors (Petrusewicz, 1983; Bujalska, 1985;Henttonem et al, 1985). Until recently most studies of this species have been mainly concerned with northern regions, while in the centre of the range the insular population has been largely dealt with (Koshkina, 1957;Ivanter, 1975;Wiger, 1979Wiger, , 1982Bujalska, 1970, 1985 andothers).…”

“…According to Bujalska (1970Bujalska ( , 1985, in an insular population of the bank vole with a relatively constant and high density, females' territo riality leads to the stabilization of the number of females involved in breeding and the number of the offspring produced in different years. It is only the age composition of mature females during summer months that changes.…”

“…Koshkina, 1957;Wiger, 1979; Hansson ei a l, 1985; Henttonen et al, 1985). In the latter variant, the density at the end of summer-autumn period is invariably relatively high and its seasonal fluctuations are pronounced (Tupikova & Konovalova, 1971; Koshkina & Korotkov, 1975;Bujalska, 1985 and others). The popula tions of C. glareolus under study were in between these extreme va riants.…”