Net production of small rodents in deciduous forest

Abstract

In deciduous stands (Tilio-Carpinetum) of the Niepolomicka Forest (Southern Poland) the numbers of rodents were estimated during four consecutive years (1967-71) by means of prebaiting and intensive removal method. Bank voles (Clethrionomys glareolus) and yellow-necked field mice (Apodemus flavicollis) constituted 92.5% of all rodents in this forest. Small rodents went in this period through a population cycle from a high density (32.1 vole and 5.9 mice per ha during the year on the average) to a low density (8.1 and 2.0 individuals, respectively). The mean number for the four year cycle amounts to 19.0 rodents/ha. When young animals staying in the nests are also taken into account the mean numbers should be increased by approximately 20%. The age of mice and voles was determined and then life tables were constructed and curves of individual growth were drawn. At high population density the mean life span of voles amounts to 2.2 and mice to 2.4 months, while at low density the corresponding figures are 2.6 and 3.3 months. The rate of body weight increase was lower in the year of mass occurrence. The turnover of individuals was also related to density and in the population of voles it ranged from 5.5 to 4.6 per year, while in the population of mice —from 5.0 to 4.0 per year. The turnover of biomass amounted on the average to 3.6/year in both populations. The number of rodents born during the year was estimated and the net production was computed from the curves of their growth and survival. In consecutive years the net production ranged from 755 to 2691 g/ha year, out of this 562 to 1977 g/ha year falling for voles and 177-755 g/ha year for mice. The mean year production of all rodents amounted to 1360 g, which corresponds to 1983 kcal/ha year. The net production of rodents was compared in a dozen or so forest and grassland ecosystems. A logarithmic describing the relationship between the production of a population and its mean year density was calculated on the example of voles population.