L. Forró szerk.: Miscellanea Zoologica Hungarica 12. 1998 (Budapest, 1998)

Horváth, Gy.: Population dynamics and trappability of four rodent species in a forest habitat

trappability during the whole period is obtained if the sum of these quotients is divided by the number of trapping occasions (5). Based on the relationship given by Krebs et al. (1969), maximum trappability was also calculated (Krebs & Boonstra 1984): -sr^ s no. caught in sample i maximum - trappability (%) = / ( ; ; : ;—

)l 00 —] no. known to be alive in sample i where n stands for the number of data collections. The relationship between trappability values and population sizes estimated based on the D-model was tested using regression analysis. Results Variation in population size In 1995-96, during the 15 four-night trapping periods 142 yellow-necked wood mice Apodemus flavicollis (Melchior 1834), 299 striped field mice Apodemus agrárius (Pallas, 1771), 31 wood mice Apodemus sylvaticus (Linné, 1758), and 89 bank voles Clethrionomys glareolus (Schreber, 1780) were caught and marked individually. During the five-night samplings between February and November 1997, the distribution of captured and marked individuals of the same four species was as follows: 306 A. flavicollis, 269 A. agrárius, 40 A. sylvaticus and 293 C. glareolus. The traps captured also a few specimens of shrews, belonging to the following three species: Sorex araneus (Linnaeus, 1758), Sorex minutus (Linnaeus, 1766), and Crocidura leucodon (Hermann, 1780). The trends in population size based on capture data from the two periods are depicted by the curves of minimum number alive (MNA) in Figs 1-2. In 1995 the monthly number of captures of A. agrárius was higher than those of the other species, and its population increase appearing in September-October exceeded by far that of the other three captured species (Fig. 1). Owing to the long and cold winter in 1995-96 and the following relatively Fig. 1. "Minimum number alive" values of four rodent species in 1995-1996