Two new papers have been published in Mammal Review this month (see Bibliography page for citations) which are interesting with respect to beavers in Britain. The first by Maeva Dewas and colleagues looks at the history of expansion and current status of beavers in France. The paper is illustrated by some excellent maps. The reestablishment of beavers on French river systems is considered a success with most river systems holding beavers and with numbers increasing. Throughout much of France, beavers have naturally recolonised or been introduced from the relict Rhone population, thus maintaining their genetic integrity. However, since 2000 beavers of different geographic origins have been spreading into the north and north-east of France from neighbouring countries which is likely to lead to introgressive hybridisation between the different forms, at least in these contact areas. The authors raise the intriguing question as what management strategies should be adopted in the future, if any, to prevent further mixing of beaver populations. In general, relict beaver populations show low genetic diversity, but populations of mixed origin, such as those in Bavaria, may be genetically more diverse and better equipped to adapt to environmental changes. However, much more research is needed on this topic. Equally if more not more important in the short-term is the discovery of North American beavers in Germany, as well as being present in Luxembourg and Belgium. North American beavers outcome Eurasian beavers and steps have been recently initiated to eradicate the alien species.
The need for more genetic data is taken up in the second paper published in Mammal Review by Frank Rosell and colleagues. It furthers the consideration about sourcing Eurasian beavers for reintroductions into Britain made by Duncan Halley (2011 – see Bibliography page). Of Halley’s three options for sourcing reintroductions, the first (using mixed stock from eastern and western European evolutionary significant units, ESU, i.e. populations considered to be distinct for conservation management) is dismissed by Rosell et al. because in contravenes IUCN guidelines. They go on and state that further research is required concerning Halley’s other two options, to use beavers from a single or mixed western ESU populations, and that considerations of practicality or money should not enter the equation.
Posted on December 2, 2011 at 10:28 am
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