8 March 2012

Species conservation: simple right?

You may think that conserving a particular species is easy, assuming that all you have to do is stick a few individuals into a zoo, breed them and then release their babies back into the wild. However, you'd be wrong and it is actually much more complex than this, with lots of unpredictable factors that only become apparent once a conservation scheme has been launched. The conservation of the black-footed ferret, Mustela nigripes, in the USA helps to highlight just this.

The black-footed ferret is a small mustelid, from the same family as European and Siberian polecats, such as weasels that were historically found across most prairie grasslands in the USA. However during the mid 20th century, the population of the ferrets began to decline and by the 1960s they were considered rare. In response to this, they were listed as endangered under the Endangered Species Act of 1973 and a conservation scheme was developed in order to help save the species. However, this took far too long and by the time conservationists were ready to implement the plan, the ferret had disappeared, seemingly becoming extinct. By chance, the species was rediscovered in Wyoming in 1985 and conservationists leapt into action to remove 6 ferrets from the wild, placing them into a captive breeding program. 

The black-footed ferret, Mustela nigripes

However, the initial excitement of capturing the ferrets soon turned into despair. Two of the captured ferrets carried canine distemper, a disease to which the ferret is unusually susceptible to and, as a result, all of the ferrets died. This meant that 6 new ferrets had to be removed from the wild for breeding, further reducing an already small population. Very small populations of a species are a major issue for conservation because the population soon becomes inbred, meaning that deleterious alleles of genes begin to build up and they lose genetic diversity. This problem, which is known as inbreeding depression, means that the species suffers from greatly reduced fitness and is less able to cope with environmental changes; thus, becoming much more likely to fall extinct.

Therefore, removing 6 additional ferrets from the population was of great concern to conservationists, especially because the wild population continued to decline. Around this time, it was discovered that the population of black-tailed, Gunnison's and white-tailed prairie dogs, the main diet of black-footed ferrets, was also decreasing due to the Sylvatic plague. With horror, conservationists realised that the main reason black-footed ferrets were going extinct was because its main source of food was declining - they should have been trying conserve the prairie dogs all of this time, rather than the ferret itself. However, by now the distribution of prairie dogs had fallen to only 2% of its historical geographical range, due to both the plague and the actions of farmers, who wrongly believed them to be pests. To make matters worse, conservationists couldn't merely focus on saving the prairie dogs because only 4 black-footed ferrets now remained in the wild!

The now endangered Gunnison's prairie dog, Cynomys gunnisoni.

To try and preserve both species, the decision was made to pull the remaining black-footed ferrets from the wild and add them to the breeding program, whilst applying the burrows of prairie dogs with a poison that would kill fleas, the vectors (carriers) of the Sylvatic plague. It was hoped that this would be sufficient to help their populations to recover. At the same time, just to be sure, they launched an education campaign in order to change the long-held beliefs of farmers that the prairie dogs were pests and that they had to be preserved, or else they could become extinct.

Fortunately, the populations of both species are now beginning to recover, even though they are both still rare. The black-footed ferret has been a particular success, with kit (baby ferrets) reintroduction schemes running since 1991. However, the species may not have been so fortunate and the case study highlights the importance of identifying why species are declining in the first place. Ironically, by trying to save the black-footed ferret, we could have easily driven it to extinction as we did not fully consider the complicating factors of the ecosystem and the full impact of humans on the ferret. This is a lesson that needs to be learnt for new species conservation schemes, elsewise they could fail, at great expense to conservation funds.

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