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Das Besiedlungsverhalten von Kleinsäugetieren auf zwei neu geschaffenen Inseln im Unteren Hasetal nach dem Ausbleiben von Überschwemmungsphänomenen

Renaturation-Pilot-Project “Hase Valley”, with the aim of restoring the natural dynamics of lowland river system, took place from year 1999 until 2003. Within this project parts of the river Hase in Lower Saxony (Germany) were restored and two river islands (Lehrte and Lahre) near Haselünne reattached to a main flow of the river. Reattaching caused flooding of both islands in each winter with exception of winter 04/05 and 05/06. From the beginning of the renaturation project small mammals on these two islands were captured yearly to monitor their migration behavior from mainland and formation of small mammal communities. The current study was performed in year 2006 from April to July continuing a last year’s work (FORELL 2005). It was expected that number of overwintered animals in year 2006 should be higher already at the start of the breading season than in past years with flooding. Species diversity was also expected to resemble year 2005. On each island animals from 3 rodent families (Arvicolidae, Muridae und Soricidae) were captured and individually marked with a passive transponder. The data showed almost no changes in small mammal community structures and its population growth in the past two years. The species diversity stayed basically the same, with no niche overlapping between the two most captured pioneer vole species (common and field vole). Only the dominance indices of two pioneer species on the island Lehrte have changed. In contrast to year 2005 where the common vole (Microtus arvalis) was the dominant species on both island, in year 2006 the field vole (Microtus agrestis) became the dominant vole species on the island Lehrte. This change is most likely due to the rash vegetation changes in June that caused a reduction of common vole habitat and led to a dominance of the field vole. In the past seven years both or one of these two vole species were always captured on the islands. The presence of other families was varying over the last seven years. Although seven years have passed from the beginning of the renaturation project and restoration of the natural dynamics of a lowland river system, there has been only evidence for a stable rodent community and vegetation development on one island (Lahre). The island Lehrte, probably due to the intensive agricultural usage before the beginning of the project, still couldn’t reach a stable ecosystem.

Kleinsäugetiere; Überflutungen; Populationsdynamik; Artenvielfalt

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