How effective are captive breeding programs?

One of the most amazing attributes that humans have is our unprecedented ability to alter our surrounding environment so that it is more suitable for our daily needs; with the most obvious of such alterations being the clearing of land to make room for housing and agricultural crops. Whilst we are not the only animals to alter our habitat (many other species such as beavers and termites also build large structures), we are the only species to build and destroy at such a large scale. The fact is that we have now spread onto every continent - even having science stations of Antarctica - and wherever we go, deforestation soon follows. The result of this is that there is very little true 'wilderness' left on Earth and many animals have lost their habitats due to our destructive ways and face imminent extinction in the near future as a result.

'Slash and burn' agriculture is an ancient way of clearing land that dates back to our earliest endeavours of farming 12, 000 years ago and involves setting blaze to, sometimes, vast acres of forest. Obviously this technique is highly destructive and displaces all of the resident organisms that were previously living there, destroying their homes. The problem is made worse by the fact that land gained in such a way is very infertile so that farmers need to create new plots of land every year.

In fact, the problem is now so bad that research undertaken during the Millennium Ecosystem Assessment (MEA) has found that in the past 50 years humans have changed ecosystems more rapidly and extensively than at any other comparable time throughout our entire history! This has resulted in a huge and irreversible loss of Earth's biodiversity and the MEA found that we have already destroyed over half of the planet's forests, 20% of its coral reefs and 35% of its mangroves - all of which are essential ecosystems for providing habitats to animals, providing ecosystem services to us and in preserving the planet's future evolutionary potential. To make matters even worse, the MEA has predicted that the degradation of ecosystems is likely to get considerably worse during the first half of this century at the very least! This loss of habitat has had profound implications on the survival of many species, which are now already extinct or are endangered and this destructive human behaviour is unlikely to change any time soon. The question then, is whether or not we should try to preserve at least some of the species and ecosystems that we are threatening and of course, many people believe that we should. As the result of this, there are countless specialised conservation organisations across the globe like the WWF and the IUCN.

One of the methods that we can use to preserve endangered species then, is via captive breeding programs in which we take animals from the wild and breed them ex-situ in institutes such as zoos and aquariums. Captive breeding programs have been very successful in the past and have been sufficient to restore the natural populations of endangered species back to relatively 'safe' numbers. A good example of this is the black-footed ferret (Mustela nigripes), which has now made a remarkable recovery after its entire population was removed from the wild and bred in captivity, with reintroduction schemes running since the early 90's. In addition to breeding rare animals in an environment that is safe from illegal poaching, captive breeding programs also allow the animals to be studied by scientists; allow the public to see foreign and exotic animals in zoos, which is both interesting and may help to raise their awareness of the importance of conservation; and furthermore, helps to maintain a 'stock' population against unforeseeable events like natural disasters (which become a huge problem if all the individuals of a particular species are only found in one place!).

These elephant tusks were seized after an anti-poaching raid in Tanzania. Sadly, despite the great efforts to protect wild elephants, illegal poaching for their highly valuable ivory tusks still goes on as is very difficult to protect wild populations. Bringing endangered species, such as elephants, into captivity however makes this much easier.

However, even though captive breeding programs sound like a good idea at first glance and definitely have their good points, are they really feasible on a large scale? The IUCN has estimated that 2, 000 - 3, 000 species of terrestrial vertebrates will have to be captive bred in the near future in order to save them from extinction and sadly, the space and money that is available globally is nowhere near sufficient enough  to cope with such an epic undertaking. Thus, we may have to decide to save some species at the expense of others - decisions that would undoubtedly be both unpleasant and controversial: why is one species more important than another?

Obviously then some animals will be more suitable for captive breeding programs than others: mainly, small creatures that can be kept and maintained cheaply in small enclosures. Amphibians are a great example of such animals and furthermore, can be easily released back into the wild because they don't have any learnt behaviours that must be taught to them in order for them to survive. This is one of the main problems with reintroduction schemes, which is particularly evident in predators - without learning how to hunt and kill their prey, captive-bred animals cannot survive in the wild and thus depend on humans for their entire lives! The fact that amphibians make such good candidates for breeding in captivity is very fortunate, as over a half of all amphibians are now endangered due to the Chytid Fungus that is killing them in large numbers across the globe and due to their extreme susceptibility to anthropogenic environmental pollutants.

The endangered black-eyed tree frog, Agalychnis moreletti, is currently being bred in captivity in Chester Zoo. The zoo is participating in an international effort called the Amphibian Ark (AArk) program that aims to preserve amphibian life and safe-guard them against their global decline.

The lack of space that is available in zoos however, sadly makes the captive breeding of large animals much less feasible than programs that incorporate smaller species. This is particularly true for large predatory mammals such as lions and tigers, which need very large territories to thrive and do not respond well to being kept in captivity. In addition, they require so much space and cost so much to keep that zoos can only afford to keep relatively small numbers of them in captivity. This means that only a small number of individuals can be bred from so that the captive populations would become vulnerable to inbreeding depression and would suffer from low genetic diversity and have reduced fitness as a consequence. To explain this further, a small breeding population rapidly becomes inbred because simply put, there are no animals available for a individual to breed with that they are not related to. Over time the population becomes more and more inbred and deleterious alleles build up in individuals. Usually such maladaptive alleles are recessive and are masked in outbred individuals who have a 'normal' and healthy allele for the gene so that they don't suffer from its effects, even if they are carrying it. However inbreeding increases the chances of an individual having two copies of the deleterious allele (which are then are said to be homozygous for the allele) so that they suffer from its ill effects - a phenomenon known as inbreeding depression.

The lion, Panthera leo, is one of the most majestic predators in the world. Sadly however, captive lions usually have extremely low sperm counts and a very high percentage of what little sperm they do produce is abnormal. This problem, due to inbreeding depression, is very common in species of big cat and is exacerbated even further by the fact they they rarely even try to mate when in captivity! Problems that makes them very unsuitable for captive breeding programs.

As well as inbreeding depression, captive breeding programs have two other serious problems. The first is that keeping many animals of the same species in a small confined space that often has poorer than desirable hygiene means that the spread of infectious diseases becomes very likely (unless a vaccination against the disease is available). This can be disastrous for the recovery efforts of a species, which is highlighted in the case study of the before-mentioned black-footed ferrets where canine distemper killed all of the first ferrets that were taken into captivity! Sadly this could easily have led to the extinction of the species as more individuals had to be removed from the wild - an example that highlights the final disadvantage of captive breeding programs: removing individuals from an already dwindling population could actually push the species into extinction in the wild, as there may be too few left to breed successfully! Unfortunately, there is no way around this problem and all conservationist biologists can do is make a decision on what they think would be best for a species in its own specific case of circumstances and hope that it's the right one!

So in conclusion, captive breeding programs are undoubtedly very effective measures for preventing species from becoming extinct. However, due to the lack of space that is available and the unsuitability of some species for such schemes, they cannot be used to save every endangered species of animal so we must also take measures to preserve them in-situ in the wild. Often, this is accomplished by protecting animals from hunting under law and by setting up designated animal reserves or parks that specifically aim to protect them and conserve nature (click here for a recent example of a national park).

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.