The species composition as it is found today is not static. Evolutionary processes like speciation are always being driven on. Especially in the European Alps, which show a relatively recent history of colonisation, migration is still going on and the ranges of different species will change. This can involve the spreading of species that expand their actual range or the withdrawal of species to small refugial areas.

The northern birch mouse (Sicista betulina) is a species inhabiting the subalpine forests as well as alpine meadows. Isolated populations in southern Germany, Austria and the Czech Republic shows the relict character of recent species distribution. It is supposed that the range of this species has been reduced to small refugial areas.

1 - Distribution of the northern birch mouse

2 - Distribution of the genetically different population types of the common vole (Microtus arvalis)

The common vole (Microtus arvalis) is a species occurring in alpine grassland as well as in lowland meadows and agricultural land. It inhabits distinctly open lands and forests can function as barriers to the dispersal of this species. Alpine populations are thought to have colonised the mountain habitat after the last ice age. After the retreat of the glaciers, forests spread and enclosed the common vole at higher altitudes. Lowland populations later followed as typical animals following cultivation. Recent investigations have confirmed that the populations from alpine habitats are genetically distinct from populations of Central European lowlands. What is remarkable is that populations from montane valleys belong genetically to the alpine group and not to the lowland group. This means, that alpine populations, kept back by the forest belt have recently expanded their range from the alpine habitats down to the lower elevations. This has been made possible by the disruption of the forest belt by human activities.

The latter example indicates the importance of new methods for investigating colonisation processes. The distinction between the two geographical seperated groups described above is based on genetic analysis. Different analytical methods exist depending on the level of investigation (inter- or intraspecific) and whether information is required only on allele distribution or also on allele phylogeny. For the research on the common vole in Switzerland, a part of the mitochondrial genome was sequenced. Mitochondrial DNA (mtDNA) is often used to assess phylogenetic relationships among closely related species or among populations of the same species. Comparing nucleotide sequences of the mtDNA genetic distances between populations can be detected, which can be correlated with geographical distance. Assuming a molecular clock, i.e. a constant mutation rate, differences in nucleotide sequences of mtDNA can be used to estimate the time elapsed since sequence divergence.

29 August 2011
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