Ábrahám Levente: Biomonitoring a Dráva folyó magyarországi szakasza mentén 2000-2004 - Natura Somogyiensis 7. (Kaposvár, 2005)

Horváth, Gy., Molnár, Dániel - Csonka, Gergely: Population dynamics and spatial pattern of small mammals in protected forest and reforested area - Kisemlősök populációdinamikája és térbeli mintázata védett erdei és újraerdősödő területen

HORVÁTH ET AL.: POPULATION DYNAMICS AND SPATIAL PATTERN 201 Table 7. Nearest neighbour distances within populations of the three frequent rodent species, with stadard deviation values, in 2003-2004 Statistical values 2003 2004 Species Mean distance (m) ± SD Mean distance (m) + SD A. agrárius 14.98 0.75 13.36 0.23 A.flavicollis 15.97 0.37 15.33 0.15 С glareolus 47.25 0JS3 12.46 0.19 However, the analysis of the distribution of individuals within the populations showed that although densities were different in the two years, individuals in all three species aimed at reaching an even spatial distribution. According to the null-hypothesis of the nearest neighbour method individuals are randomly distributed. Yet, results of the two years showed in all three species that this hypothesis should be rejected, the distribution of individuals being even. In terms of the average distance of nearest neighbours, the bank vole had significant difference between the two years, indicating that individual territories were further apart in 2003 when densities were low. The two Apodemus species are known to have larger home ranges and are capable of covering considerable distances, yet the average distance from the nearest neighbour was almost the same in the two years, for both species (Table 7.). It must be emphasised for Fig. 5 above that it is created from cumulated data, and besides the fact that spatial distribution is density dependent, it is also important to find out how space use and spatial patterns transform as population sizes change throughout the year. For such analyses monthly data should have contained higher capture values, thus the seasonal changes of spatial distribution were analysed from our 2004 data only. For the closed alder gallery forest and the regrowing forest area it was assumed that due to the difference in resource distribution and interspecific competition, the two habitats are used by the various species taking turns, therefore considerable migration and partial population translocation can be measured among the two areas. For the analysis of the assumed population translocation between the closed forest and the regrowing plot, i.e. between two areas with dissimilar physiognomic structure, the daily capture data of the three populations in the two plots were charted on a graph so that the daily and monthly changes in population dynamics can demonstratively indicate changes in space use (Fig. 6.). In the case of yellow-necked wood mouse, even the August data were remarkable, as capture maxima in the two areas appeared distinctly even within the fiveday trapping session. In the closed forest, the capture peak occurred in the first few days, whereas in the regrowing plot it commenced in the second half of the period. From data of the two autumn months it clearly appears that individuals of the population tended to leave the regrowing area and occupied the closed forest where the spatial arrangement of the population then stabilised. For the striped field mouse, capture maximum clearly occurred in August in the regrowing plot, with its abundance decreasing gradually in the closed alder gallery forest, to disappear completely from this area by November. In the more open habitat its spatial structure stabilised, its abundance not reaching the August maximum. The population of bank voles in August-September had higher abundance in the closed forest, then in November it had higher capture rates in the regrowing plot (Fig. 6.). Looking at the trend of population sizes throughout the months, the most striking shift between the use of the two habitats was observed in the case of the yellow-necked wood mouse and the striped field mouse. As to the bank vole, its appearance in the regrowing plot is a result of dispersal, shown by the fact that a part of the population, with similar size to that migrating to the open area, stayed in the closed forest. Emigration from the closed alder gallery forest can be assumed, even if capture coordi-