IVth International Conference on Dormice (Rodentia, Gliridae)

POPULATION DYNAMICS OF THE COMMON DORMOUSE (MUSCARDINUS AVELLARIUS L.): POSSIBLE PATTERNS OF REGULATION

Juskaitis, R.

Institute of Ecology, Akademijos 2, LT-2600 Vilnius, Lithuania. e- mail: juskaitis@takas.lt

M. avellanarius is unusual in being a relative k-strategist among small mammals, and its strategy is based on long life, low recruitment rates and low population density (Bright, Morris, 1996). The aim of this paper is to discuss the population dynamics of this particular species and to present possible patterns of density dependent regulation. Population dynamics is defined not only as abundance dynamics, but also as the dynamics of population demographic structure, reproduction, mortality, territorial distribution etc. Data on long-term population dynamics of M. avellanarius are scant, and only data by Likhachev (1966a, 1966b) from the Moscow region are suitable for comparison with the results obtained at study sites A and B in Lithuania (Juskaitis, 1994, 1997, 1999a, 1999b etc.).

The abundance dynamics of the M. avellanarius populations investigated were comparatively “smooth”: there were no sudden changes and no more than three alterations in abundance recorded in two successive years (Likhachev, 1966a; Bangura, 1987; Juskaitis, 1994). Population abundance dynamics were connected very closely with the process of reproduction, and reproductive intensity (percentage of reproducing females, number of litters, litters size) was the most important factor in population regulation. Different strategies of reproduction (percentage of reproducing females, timing of births, number of litters) were observed in M. avellanarius populations investigated in Lithuania and in the Moscow region (Likhachev, 1966b; Juskaitis, 1997).

A pattern of regulation based on the intensity of reproduction was evident at site A, where spring population density fluctuated by about 1.0 ind./ha (0.7-1.5 ind./ha). The percentage of breeding adult females was inversely proportional to population density in spring in separate years. Evidence of a decrease in reproductive intensity was inferred by high spring density in 1985 (also in Moscow region in 1958). Reproductive performance affected the population density in autumn as well as the age structure (i.e. percentage of young in the population) directly.

This reproductive intensity based pattern was less evident at site B where average spring population density was 0.7 ind./ha (0.5-1.0 ind/ha). Population abundance was restored in a different way at site B in 1987-1988 when spring population density was very low (0.5-0.6 ind./ha). Females were significantly more common than males in the litters resulting from a period of very low reproductive intensity in 1987. In spring 1988 changes in territorial distribution occurred: the population split into separate territorial groups (Juskaitis, 1990). Average population density was very low, but in separate territorial groups the density was normal (more than 1 ind./ha). After these changes the intensity of reproduction increased, and population abundance was consequently restored.

When population density decreased the following tendencies could be observed: the females born in the same year joined the breeding process (Juskaitis, 1997), and the proportion of females in the adult population increased slightly (Likhachev, 1966a; Juskaitis, 1999b).

Long-term stationary investigations in different part of M. avellanarius distribution area are necessary for further elucidation of this question.

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