Is captive breeding a valuable tool in the conservation toolbox?
An ever expanding human population is putting increased pressure on endangered species and driving many to extinction. It is for this reason that the conservation of rare and endangered species has come to the forefront of our attention over recent decades. There are a number of strategies that exist to conserve these species at risk. The success of captive breeding as one such strategy for the conservation of endangered species is often contested. Here I discuss the issues, limitations and improvements surrounding captive breeding to come to a conclusion as to whether it is a valuable conservation tool or whether it is simply acting to ‘lock away’ species until inevitable extinction.
Captive breeding for conservation aims to rear sustained populations that will potentially be ready for reintroduction to the wild in the future (Williams & Hoffman 2009). It was originally used for the conservation of only the most critically endangered species (Araki et al. 2007) however its use has now spread to the restoration of many declining natural populations – this may explain why the emphasis on captive breeding in recent zoo and conservation biology literature has dramatically increased (Bowkett 2009) with one review suggesting that as many as 64% of species recovery plans in the US should employ captive breeding (Tear et al. 1993). Captive breeding is used in a number of conservation techniques, including: supplementation –captive-bred individuals are regularly added to an endangered natural population (Lynch & O’Hely 2001); supportive breeding –the size of a wild population is augmented by breeding part of that population in captivity and releasing the captive-bred progeny back into the natural population (Ryman and Laikre 1991); and reintroduction – an attempt to establish a species in an area that was once part of its historic range (IUCN 1998), using individuals from captive populations. It is worth mentioning also that captive breeding in zoos, although not necessarily geared towards reintroduction, plays hugely important roles in the education and research aspects of conservation management (Pinder & Barkham 1978).
Is it a success story?
In zoo captive populations, it is considered a success when the captive population continues to increase, without the addition of wild-caught animals (Pinder & Barkham 1978). The success of reintroduction to the wild involves a combination of factors: breeding by the first wild-born population after reintroduction, recruitment exceeding adult death rate after three years, an unsupported population of at least 500 and establishment of a self-sustaining wild population (Seddon 1999). Unfortunately, even though captive breeding and reintroduction has the potential to save many species from extinction, reintroduction programs using captive-bred individuals have very low success rates (Mathews et al. 2005). A meta-analysis by Williams and Hoffman (2009) found that only 13% of mammal reintroductions from captive-born populations were successful compared with 31% of translocations using wild-born individuals. The successes in saving species from extinction over the short-term are often well publicised (e.g. California condor –, Toone and Wallace 1994; Guam rail – Derrickson and Snyder 1992; black-footed ferret – Miller et al. 1996,) and it is easy to be caught up in the publishing bias (Jule et al. 2008) and forget that the large majority of reintroductions are failing. Perhaps these failures could be reversed with knowledge of the limitations facing captive breeding for conservation.
What is holding us back?
Failures in reintroduction after captive breeding can be attributed to three main factors: 1) meeting the costs and requirements of captive breeding, 2) genetic effects of captive breeding, and 3) premature use of captive breeding.
- Very few taxa have successfully bred in captivity owing to a lack of physiological and environmental requirements (Snyder et al 1996), needs that are often not met due to a lack of funds (Matthews et al. 2005). Derrickson and Snyder (1992) suggest that the costs of keeping animals in captivity can reach half a million dollars a year per species and in many cases securing enough funding to ensure that the captive environment closely resembles the natural environment, whilst also meeting animal welfare standards, is just not possible. The nature of keeping animals in captivity exposes them to a high disease risk (Snyder et al. 1996), as often they are kept in close proximity to species harbouring exotic diseases. To overcome this risk adds yet more costs to the process and so is rarely achieved effectively. If breeding in captivity is successful and the habitat requirements are matched to those experienced by the species in the wild there is still an issue when it comes to reintroduction of finding suitable habitat within the species’ known range in order to ensure the best chances of survival (Pinder & Barkham 1978).
- The genetic effects of captive breeding are numerous. As captive populations are generally small and comprised of related individuals, inbreeding depression becomes a problem (Ralls and Ballou 1986) leading to a high frequency of deleterious alleles that may be expressed as decreased fitness in the wild. Behavioural changes associated with captivity can very quickly become genetically selected for, often over few generations (Araki et al. 2007). This is domestication selection and can have large impacts on the fitness, and therefore sustainability, of a population upon reintroduction (Lynch and O’Hely 2001). Jule et al (2008) found that in captive-bred carnivores, those that were captive-born were more susceptible to starvation, predator avoidance and disease when reintroduced to the wild than those that were wild-caught, demonstrating that a life in captivity can negatively influence an animal’s ability to survive in the wild.
- Funding competition between in situ and ex situ conservation efforts often leads to captive breeding pre-empting efforts in the wild (Conway 1995). Captive breeding is frequently used prematurely to divert attention from the real issue causing a species decline, for example in the USA the captive breeding of black-footed ferrets was highly publicised, to hide the fact that all their habitat was being destroyed through other government programs (Miller et al. 1996). Similarly, millions of dollars are invested annually in the conservation of salmon in the north west USA instead of addressing the cause of the decline – habitat alteration due to hydropower dams (for more information see http://www.fws.gov/salmonofthewest/dams.htm). In reality, directing attention to the natural habitat and addressing the initial reasons facing a species requiring captive breeding for conservation may be more effective than attempting reintroduction from captive populations, else the same pressures will exist that created a problem in the first place. Sadly captive breeding is too commonly used as a ‘quick fix’ that ignores the problems rather than tackling them.
Addressing the issues
- Overcoming the financial costs and logistical restrictions of captive breeding is quite unlikely; however this issue could be addressed by minimising the need for captive breeding and instead focussing on in situ conservation efforts. In fact it has been shown that the cost of conserving mammals ex situ often exceeds the in situ costs even when there is intensive protection (Balmford et al. 1995). There has recently been a big increase in the capacity of zoos to contribute directly to in situ conservation (Zimmerman & Wilkinson 2007) largely due to increased availability of funds. These projects (for example Colchester Zoo and the UmPhafa Nature Reserve: http://www.umphafa.com/about/about-umphafa) are acting not only to improve or maintain suitable habitats in situ but also play a big role in educating the public worldwide about the importance of conservation.
- It is important to focus on minimising the genetic effects of captivity. This can be done through carefully planned breeding strategies that maintain diversity and reduce selection for the captive environment. Reducing the number of generations spent in captivity will lessen the number of generations that selection can act upon. Delaying reproduction in species where reducing the time in captivity is problematic can be achieved through the use of contraceptives and cryopreservation of germplasm (Williams & Hoffman 2009) however these methods are again costly. Another solution to maintain genetic diversity is to subdivide the total captive population (Ralls & Ballou 1986) and supplement these smaller subpopulations with wild immigrants to reduce inbreeding depression (Williams & Hoffman 2009), thus within-species diversity is maintained despite a loss of diversity within subpopulations.
- Many governments have funds available to allocate to conservation projects, however often the very need for conservation is fuelled by opposing government-led projects (for example, prairie-dog eradication programmes have reduced the black-footed ferret populations to captivity (Miller et al 1996)). The solution here lies in the responsibility of NGOs and private investors to contribute to conservation efforts globally.
There are situations in which captive breeding has played a pivotal role in preventing the extinction of species, however there are many more situations in which it has failed. It should be used as a last resort strategy in species recovery because of its large, negative genetic and phenotypic impacts. That is not to say it shouldn’t be used in conjunction with broader conservation measures. It is widely agreed that the best way to improve the success rate of reintroductions from captive breeding programs is to address the issue that drove the need for captive breeding. Conservation of ecosystems and habitats, and the removal or reduction of threats to endangered species will ensure that captive breeding doesn’t become the long-term solution it threatens to be. Until the in situ issues surrounding endangered species are addressed we risk locking these species up for good.
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