L. Forró szerk.: Miscellanea Zoologica Hungarica 12. 1998 (Budapest, 1998)
Horváth, Gy.: Population dynamics and trappability of four rodent species in a forest habitat
monthly from February to November, yielding 6050 trap nights. Thus, the analyses are based on results from a total of 10910 trap nights. Traps were checked twice daily both in 1995-1996 and 1997: starting at 7 00 CET and 19 00 CET, totalling 7 and 9 checks, respectively, within one trapping period. Traps were left set up during daytime hours, too. Bacon and whole cereals mixed with vegetable oil or aniseed extract were used as bait. For individual identification of the animals toe clipping (Begon 1979, O'Farell 1980, Nichols & Conley 1982) was used. When an animal was trapped, its sex, reproductive status, age and weight were recorded. Variation in population size Data of the 15 four-night trapping periods in 1995-1996 were recorded in a Manly-Parr diary of captures (Manly & Parr 1968). Temporal changes of population sizes were monitored using the index "minimum number alive" (= MNA) (Petrusewicz & Andrzejewski 1962, Krebs 1966, Boonstra & Krebs 1978). The modification of the trapping regime in 1998 resulted in an improvement of capture success. Accordingly, the methods of data processing also needed revision: to replace the Manly-Parr capture diary we worked out in Microsoft Access a database system from which queries can be made on capture-histories. For estimating population size, the Jolly-Seber estimator for open populations was used with help of the JOLLY computer programme (Hines 1988) which runs tests on data using various models in its calculations (Pollock et al. 1990). Population size (Af.) was calculated based on the D-model of the programme. This model maintains constant capture probability, a basic criterion of the Jolly-Seber estimator, throughout the study period, and it is reduced in the interpretation of survival probability too, i.e. this parameter is also considered constant by the model. The relative accuracy of the estimation (i.e. coefficient of variation of N: cv(N) (White et al. 1982)) was calculated using the standard error of Nf. The comparison of MNA-trends was made for species-pairs in each period, using Spearman rankcorrelation (Zar 1996). Trappability and daily capture data Before calculating the trappability index, the trapping success of the two different types of traps was tested. The capture data of wooden and plastic traps were compared in both trapping periods, for each captured species, by the heterogeneity test. Results from the morning samplings in the four-night and five-night periods were compared using the KruskalWallis analysis of variance, based on the ratio of mean number of morning captures and the number of recaptured individuals recorded during the morning samplings. From the estimated number of marked individuals (M ( ), Jolly trappability was calculated (Krebs & Boonstra 1984): The value M i is calculated by the JOLLY programme; the number of recaptured animals can be summed for time i from data in the Manly-Parr diary and the database capture history tables (27y y ). The quotient Zy { /M- gives the value of Jolly-trappability based on the i-th sample. Percentage value for cv(N) = SE(N) N Jolly - trappability (%) = 100 S
