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ŠUMARSKI LIST 3-4/2012 str. 38     <-- 38 -->        PDF

striped field mouse, a species that can have much higher dispersal movements (Liro & Szacki 1994). Yellow-necked mice travel significantly greater distances than the bank vole, a species characterised with the smallest movements in the comparison of the three rodent species. The movement distance of species is determined greatly by the species’ typical seasonal dispersal pattern which occurs mostly in two different periods (spring and autumn) according to earlier studies in population of the yellow-necked mouse and the bank vole. The bimodal pattern of dispersal suggests that the two waves of dispersers move because of different reasons and those characteristics of dispersing individuals differ in the two periods of the year (Gliwicz 1988, 1992). According to our examinations the dirt road which divides the trapped forest into two parts has no barrier effect in case of the specimens of the three rodent populations. According to the study of Bakowski & Kozakiewicz (1988) a road which goes through a forest limits the movement of bank vole but has no effect on the movement of yellow-necked mouse. When studying the long-term movement of striped field mouse there was no significant difference in the sex, weight and the reproductive condition of the individuals that travelled long distances. Studies in a fragmented forest of Southeast Asia have also confirmed that the striped field mouse is less sensitive to the presence of roads then the related species (Apodemus peninsule). These studies showed that the roads have different effects on different small mammal species which affects their habitat selection (Rhim et al. 2003). Our results performed along River Drava showed that the striped field mouse used the two forest areas with of the same intensity and dispersed in the whole study area which contributed to an absolute dominance in the small mammal community. Because the intensity of the dispersal can increase together with the density of the population (Kozakiewicz 1976), the periods of seasonal dispersal patterns determine the number of movements across the road. The lower population density results in lower number of movements across the road. Bakowski & Kozakiewicz (1988) trapped in August which is a high-density period of the bank vole, thus the results justified even more the philopatry of bank vole which is also described by other studies (Mazurkiewicz 1994).
Long-term botanical studies of willow stand fragments in floodplains of River Drava have pointed out, that the coenological characteristics of the plant community changed from year to year. The analysis of data from the surveys together with field observations has clearly shown that these changes were closely related with changes in the water supply of the studied habitat (Juhász & Dénes 2005). Small mammals respond rapidly to such changes, thus they are good indicator objects in the study of natural and anthropogenic disturbance factors to the vegetation structure of forests. The spatial and temporal pattern of small mammals in floodplain forests is determined at the greatest degree by the fluctuation of water levels, the frequency of floods, and the duration of periods between high flood waves. Changing water levels as an ecological constraint factor can mean temporary habitat loss for small mammals and the shrinkage of dispersal possibilities. When flooding recedes and the negative constraint disappears, small mammals use different recolonisation strategies to spread in the floodplain area once again, in which various characteristics of the landscape play an important role (Wijnhoven et al. 2006).
Spatial behaviour may reflect population dynamics (Wiens et al. 1993), thus the relative habitat use and the spatial association of coexistent small mammals have been important research areas since long time ago. These contribute to understanding the environmental needs of different species and the intra- and interspecies relationships of these small mammals.
In the examined floodplain willow-poplar grove forest next to River Drava, the following conclusions were drawn from the CMR-trapping monitoring performed during the period between two substantial floods:
The species composition and species abundance values of the small mammal community in the floodplain forest were different in the three sampling years. The species number of the small mammal assemblage varied between 6 and 10, suggesting that species abundance can change in the short term as well, depending on environmental factors.
The dirt road had no barrier effect in the movement of individuals of the studied populations. Although the calculated area preference values showed variation among the years, our results suggested that a spatial segregation strategy was present in the relationship between bank vole and the two wood mouse species. These results confirmed the findings revealed by former investigations looking at competition and spatial relationships. As the space occupation of the water shrew increased, a significantly positive preference for areas along the Drava was found, confirming the association of this species with wet areas.
Our results obtained along the River Drava for the habitat generalist striped field mouse, a species often used as a model in movement pattern research, show that this species used both sides of the forest areas divided by the dirt road with the same intensity, dispersing in the entire studied forest, this behaviour leading to absolute dominance by this species within the small mammal community.
During the period between the two major floods, differences between yearly spatial relations among the dominant small mammals suggested fine differences in their strategies, expressed in interspecies relations, which allow the lasting co-existence of various small mammals in the rapidly changing, heterogeneous environment of floodplain forests.
Monitoring activities were supported by Dunav-Drava National Park Directorate. We are grateful to Jenő Purger for the Cro­atian translation.