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| ŠUMARSKI LIST 3-4/2012 str. 37 <-- 37 --> PDF |
Discussion Rasprava In the present study we examined the spatial distribution of the small mammals of a willow-poplar floodplain forest by the upper River Drava located along the south-western boarder of Hungary, based on a three-year long live trapping (summer and autumn). Only fragments have remained along the Drava of the studied floodplain forest type, a hygrophilous azonic forest in the coastal zonation. In terms of the survival of the species, it is forest interventions (e.g. clear-cutting), dynamic changes in water level and thus the flooding of the forest areas that are the most important constraint variables. The effects of dynamic changes of environment as an ecological constraint are particularly important in case of terrestrial species on the floodplain areas. The heterogeneous landscape may change the spatial dynamics of species at the regional scale and consequently their local scale distribution and abundance (Ricklefs 2008). Small mammals represent an important component of these floodplain forest ecosystems. Therefore several researchers have studied the spatial-temporal patterns of terrestrial small mammals and took into consideration the effects (e.g. periodic floods) and processes (colonisation, recolonisation) in the former floodplain forests (Andersen et al. 2000, Wijnhoven et al. 2005, 2006). In our examination, we captured the striped field mouse in the largest quantity which is a species capable for expansive dispersal. Haferkorn (1994) detected six small mammal species in the floodplain forest among River Elbe. Similar to our investigation the bank vole, the yellow-necked mouse and the common shrew were typical among the Elbe, but there the bank vole was the most common species. In the floodplain forest among Drava, bank vole was the second species of the dominance ranking. Mazurkiewicz (1994) pointed out that bank vole is numerically dominant in small mammal communities in temperate forests. Based on our studies among the upper section of Drava, bank vole was an absolutely dominant species in a lowland alder gallery forest (Paridi quadrifoliae-Alnetum) lying close to River Drava (Horváth et al. 2005). However, in our present study the dominance of bank vole was much smaller than the dominance of the striped field mouse in the examined floodplain forest (Salici-Populetum). Comparing our data from Drava’s floodplain with data of Haferkorn (1994), there were greater differences in the appearance of rare species. By the Elbe banks e.g. the pygmy shrew (S. minutus) and the harvest mouse (M. minutus) were rare species, among which the harvest mouse did not appear in the floodplain forest along Drava, however depending on the water supply some shrew species appeared as rare species. Crocidura spp. (Lesser white-toothed shrew, bicoloured white-toothed shrew) indicated the drier periods while the water shrew (N. fodiens) indicated the wetter ones. In the Netherlands Wijnhoven et al. (2005) researchers trapped seven small mammal species from which five proved to be common. Common vole and bank vole occurred with the greatest density in that area. During the investigation they found major difference in the recolonisation of different small mammal species between two consecutive floods, which correlated with the quality and range of available habitat patches. In our studies the sampling transects were arranged perpendicular to the Drava and followed the water gradient between the river and the river terrace. Our result showed that the success of acceptability of observed species does not depend on the spatial arrangement of transects. However, when analysing the annual data we obtained differences in the area preference of the various species. The habitat use of the two mice (A. flavicollis, A. agrarius) were the same, while the habitat use of bank vole was contrary; the vole mostly preferred the area between Drava and the dirt road, which suggested the spatial segregation of the bank vole and the two Apodemus species. These results confirmed the earlier studies of interspecies competition and spatial patterns (Gliwicz 1981, 1984; Mazurkiewicz & Rajska-Jurgiel 1998). Studies of the habitat selection of bank vole showed a preference towards older forest stands with dense ground cover in the form of undergrowth and dead woody material, providing food and coverage (Mazurkiewicz 1994, Miklos & Ziak 2002). Previous studies dealing with the population density and the spatial patterns showed that the density of yellow-necked mouse was always higher than the density of bank vole in smaller isolated forest patches (Rajska-Jurgiel & Mazurkiewicz 1988, Rajska-Jurgiel 1992), although the bank vole reached much higher densities in extended forests (Mazurkiewicz & Rajska-Jurgiel 1987). The bank vole is considered as an immovable species (Mazurkiewicz 1971, Löfgren 1995), while the yellow-necked mouse is more mobile (Bergstedt 1966, Mazurkiewicz & Rajska-Jurgiel 1987, see also Andrzejewski & Babińska-Werka 1986, Kozakiewicz & Szacki 1995, Liro & Szacki 1994). The mice are specialist from the perspective of habitats and live in alder texture forests (Montgomery 1980; Gurnell 1985). The movement distance of striped field mouse had the highest standard deviation but despite of this, yellow-necked mouse covered significantly greater distances than the specimens of |