Friday, April 8, 2011

The Decline of the Adder in the United Kingdom


Recent reports from the UK suggest that the only venomous snake found on the island nation is in serious trouble. Herpetologists from Natural England, Zoological Society of London (ZSL) and Oxford University have teamed up examine the status of  the  Adder. In the last decade it has declined, and surveys suggest a third of remaining adder populations may comprise fewer than ten adults, and likely results from degradation and fragmentation of habitat. Small populations, particularly in the English Midlands, are not capable of maintaining a healthy level of genetic diversity, which makes them less resilient to disease, and make them more susceptible to enetic defects, which in turn could lead to local extinctions. Dr Trent Garner, Senior Research Fellow at ZSL’s Institute of Zoology is quoted as saying, “Genetic diversity has been shown to be a key component for successful adder populations in Sweden and Hungary, but has yet to be studied in the UK. Our goal is to provide the first insights into how population size and isolation may be related to genetic diversity of the UK’s adders.” Jim Foster, herpetologist for Natural England, said, “With around a third of adder populations now restricted to isolated pockets of habitat, and with only a handful of snakes per site, they could be especially vulnerable. As we have seen with natterjack toads, populations that are small and isolated can start to decline purely through genetic effects. This ground-breaking study will see if adders are suffering a similar plight....Fortunately, if there are problems we still have time to deploy a number of conservation remedies. Habitat restoration and the creation of wildlife corridors will help get these snakes back on the move. We may even consider moving adders between populations, to artificially promote “gene flow” - although that carries risks and we’d need to look more closely at the genetics results before proceeding.” [Photo: The Adder, Vipera berus. Photo Credit: Marek Szczepanek].


Tobias Uller of Oxford University’s Department of Zoology agreed, saying, “When populations become small and isolated, with it comes the risk of expression of harmful genetic variants that normally remain ‘hidden’ in larger populations. Loss of genetic variation may also compromise the population’s ability to evolve – a problem that is particularly acute when habitats change rapidly or if a new disease emerges.”


The Adder is one of four reptiles  species described as "widespread" because they are scattered over a large area in Britain. It can be found from the south-west England all the way north to Scotland. But this not dose not mean the species is abundant, within their large distribution, they are restricted to grassland, scrub and woodland edge, primarily on sandy soils.


In 2004, English Nature (now Natural England) surveyed naturalists around the country asking them to evaluate the health of Vipera berus populations, the results suggested "disturbance" was the greatest threat. A third of the populations were small (estimated as fewer than 10 adult snakes), and a third of the populations were isolated. Population declines and extinctions tended to be more frequent in small and isolated populations.


Make the Adder Count, is a project encouraging local Adder conservation and long-term monitoring of populations, information from a small but dedicated band of Adder-watchers around the countrymay be able to alert conservationists of populations in trouble. Disturbance can have different causes. In some cases it is destruction of habitat, but the snakes are still being killed by humans. And, disturbance can also result from people visiting well-known adder sites.
References
Baker, J. 2011. Why we must make the adder count. guardian.co.uk
Surfbirds.com, April, 3, 2011.

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