Life on the Edge of a Habitat Is Dangerous

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flickr user: NASA's Marshall Space Flight Center

Author: Helmholtz Centre For Environmental Research

The transition of climate and land use has resulted in more and more animals and plants being forced back into ever smaller habitats, which are ever further apart. In the center of their range, they can populate a wide range of habitats, but on the edge they need special biotopes with particularly favorable characteristics. Species with particular needs find it especially difficult to overcome the distances between these refuges. So they are often only to be found in small, isolated populations, with little contact between them. The genetic variability of their members is therefore correspondingly low. “For that reason, such populations adjust badly to new climatic conditions, parasites or other challenges,” explains Prof. Klaus Henle from the UFZ. The risk of extinction increases.

Populations at the edge of a range are therefore more specialised and more sensitive. In this context, do they also react more sensitively to fragmentation than members of the same species in the center? Previously, such comparisons had only been drawn between different species. Nobody knew whether these differences also existed within the same species. Klaus Henle and his colleagues have now investigated using the example of the sand lizard.

The small reptiles, found from central France to Lake Baikal, and from southern Sweden to the Balkans, have a preference for relatively open landscapes with individual trees and shrubs. That could be, for example, dry grassland, moorland or embankments. So that it does not get too hot for them, they need more shady vegetation in their more southerly areas of distribution than in central Europe. In Scandinavia, on the other hand, they restrict themselves to particularly warm and sunny locations.

The Sand Lizard Example

In order to test their hypothesis — that animals of one species living in the center of their range handle fragmentation of their habitats better than those on the periphery — the researchers investigated five sand lizard populations in Sofia, at the most southern edge of the range of this species, and eleven populations in Leipzig, which is more or less in the middle of the lizards’ range. “In both cities, the animals are confronted with fragmentation,” says Klaus Henle. Since the end of the 20th century, Sofia has seen a veritable boom in construction. This has meant that in the last ten to fifteen years, not only have many green spaces in the Bulgarian capital given way to residential and industrial areas, but in addition, the large parks have been divided up by new buildings, meaning that individual areas, along with their scaly residents, are now isolated from one another. Although in Leipzig about half the area of the city still consists of green spaces, not nearly all of them offer suitable lizard habitats. In the Saxon city, too, there are therefore populations that live more than four kilometres apart. But based on previous experience, the small reptiles can hardly manage larger distances.

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