Herkomst en verspreidingsgeschiedenis van de noordse woelmuis (Microtus oeconomus (Pallas, 1776)] in West-Europa, in het bijzonder in Nederland

摘要

Origin and distribution history of the root vole (Microtus oeconomus (Pallas, 1776)) in Western Europe, particularly the Netherlands.An attempt is made at reconstructing the postglacial colonisation routes of the root vole (Microtus oeconomus) in western Europe, especially those leading to the Netherlands, on the basis of the former and present geographical distribution. During the Salien and later during the Weichselien ice ages, vast areas of glaciation formed in these mountain ranges, with permafrost plains to the north and south. The glaciers caused large flows of meltwater in spring and early summer, which carved their way through the permafrost areas and inundated low-lying plains. Marshy conditions caused by these floods and by the thawing of the top layer of soil allowed for plant and animal life to thrive in this active layer of seasonal thaw. The vegetation structure of these arctic grasslands was very similar to alpine grasslands, allowing root voles to switch from one to the other biotope. Root voles at this point had probably evolved towards a more modern form, which due to its larger size and preference for lower soil temperatures (25.4 °C) had become adapted to a year-round life in the tundra. In each of the mountain ranges where root voles originated, populations went through bottlenecks, leading to genetically distinct groups.Along the Rhineand Meuse rivers, root voles reached the areas around the mouths of these rivers, where they have managed to survive until this day. Along the middle and lower reaches of the Rhine and Meuse rivers, natural environmental conditions such as these were destroyed by hydraulic engineering projects in the last century, causing the disappearance of possibly the last populations of root voles on the Niederrhein in Germany and the Meuse in Noord-Brabant in the Netherlands. There appear to be major differences between root voles from the north, middle and southwesternNetherlands, both genetically and morphologically. Further study could reveal whether these differences have any relation to the different areas of origin and postglacial colonisation routes.Moreover, separate populations of root voles in the Netherlands show so much difference in coat colour that they can hardly be placed under one common denominator. Further study of morphological and genetic differences could shed more light on this, as well as on the origins of the various populations. In the northern European (southern Norwegian and Swedish), eastern European, Asian and North American parts of its distribution, where large melt-water rivers still flow through areas with continuous or discontinuous permafrost, conditions persist which are similar to those during the ice ages and root voles still occur in large continuous areas. Elsewhere and particularly in western, middle and northern Europe, the species was only able to persist where marshy sedge and reed vegetation occurs due to high groundwater levels and floods during spring and the start of summer, maintaining the cool conditions root voles prefer.In the Netherlands, the root vole spread further inland from the onset of the Holocene along coastal areas where perimarine conditions had formed on the edge of salt and fresh water tidal areas. Given the expectation that the level of the sea will continue to rise in the future, ever largerhydraulic engineering projects will need to be undertaken to prevent flooding by the sea and by rivers, and Dutch root vole habitat will be threatened further. However, since the root vole enjoys a biogeographically unique position within Europe and is acharacteristic species of the Dutch delta, it should receive special attention and protection during both planning and implementation of these projects.