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

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

MISCELLANEA Tomus 12. ZOOLOGIC A 1998 HUNGARICA p. 107-119 Population dynamics and trappability of four rodent species in a forest habitat by Gy. Horváth (Received May 28, 1998) Abstract: Trappings were carried out in a forest (Querco robori-Carpinetum) habitat on the Dráva Lowlands in two periods, using the capture-mark-recapture method. The sampling grid in the 1 ha study area contained 9 by 9 trap stations for 15 months in 1995-1996, and 11 by 11 stations for 10 months in 1997. A total of 10910 trap nights were recorded in the two periods, during which 71 wood mice (Apodemus sylvaticus), 448 yellow-necked wood mice (Apodemus flavicollis), 568 striped field mice (Apodemus agrárius) and 382 bank voles (Clethrionomys glareolus) were marked. Changes in the numbers of rodent populations were characterized using MNA="minimum number alive" and abundance values obtained by the Jolly-Seber estimator. The latter yielded higher values than MNA in the four-trap-night periods and lower values than MNA in the five-trap-night sessions. For the ratio of morning mean number of captures vs. recaptures by species, significantly better results were obtained in the five-night periods. Key words: live trapping, population dynamics, Jolly-Seber method, trappability, Apodemus, Clethrionomys Introduction Within the framework of the International Biological Programme (IBP) small mammal research played an important role. Besides the main aims of the programme, such as the investigation of the function of small mammals in ecosystems and trophic structures, the analysis of their productivity etc, methodological considerations of trapping were also brought up (Ryszkowski 1969, Hansson 1975, Flowerdew 1976). Several investigations and case studies dealt with the relationship between the size of the trapping grid and the edge effect (Pelikan 1968, 1970, Ryszkowski 1971, Smith et al. 1971). Separate studies were devoted to the effect of trapping grid size, which influences density estimations on the one hand (Aulak 1967, Smith et al. 1975, Jensen 1975), and is of crucial importance in home range calculations and small mammal movement analysis on the other (Hansson 1969, Zejda & Pelikan 1969, Bondrup-Nielsen 1983). The technical background of live trapping (trap types, their applicability, effect of baiting, etc.) was a cardinal issue, too. Besides case studies (Kisiel 1972, Dalby & Straney 1976, Maly & Cranford 1985, Getz et al. 1986), several earlier and more recent general studies have been published on trapping methodology (Bateman 1971, Gurnell & Flowerdew 1990, Barnett & Dutton 1995). These issues seemed to raise the problem of defining trappability, thus, in addition to formulating estimators for population size and density, trappability was also the subject of scrutiny and several indices have been worked out (Andrzejewski et al. 1966, Krebs 1966, Krebs & Boonstra 1984). When evaluating trappability indices, Nichols (1986) suggested the use of maximal trappability estimation. This method of estimation was