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The process of moving individual animals from one site to another, such as from the wild to a zoo for the study of conservation is an increasing tool to re-establish threatened populations (Roe et al, 2010). There are a range of issues with the reintroduction of captive bred individuals in order to increase a wild population that is decreasing due to a range of factors. Ex situ conservation involves the removal of individuals or groups from the natural habitat into captivity. This is either to maintain a genetic stock or for a range of breeding programmes. Although it has been found that it is relatively easy to keep a range of animals in a captive environment, but there are large amounts of difficulty when it comes down to trying to breed them (Pullin, 2002). Until only recently zoos and other wildlife institutions have made conservation breeding programmes more important, and some of these breeding programmes have the intention to reintroduce the offspring back into the wild. The number of individuals released from captive breeding is normally quite small, although it is becoming more common in order to try and decrease the amount of inbreeding that may occur within the wild populations (Jamieson, 2011).
Issues with captive breeding and the reintroduction of species
Captive breeding has both a range of advantages and disadvantages (table 1), including the need to increase a species population size and reducing the risk of extinction within the wild. By using captive breeding within zoos, means that there is less of a need to remove individuals from the wild to study as it allows people to understand the species without removing large amounts of individuals from the wild causing a decrease in population size. Unfortunately there is a large amount of disadvantages with captive breeding compared to the advantages. This includes removing the last few remaining individuals from the wild, which could cause the species to become extinct in the wild even if the idea was for the reintroduction of the animal. Also getting the animals to breed in the first place is also very expensive; this is to ensure that the facilities are appropriate for the animals. Because the animals are bred in captivity it means that there is a large chance of the animals inbreeding together if breeding wasn't controlled, this could also affect the natural selection of the species and means that the genetic stock is reduced. The main objective should be for all captive breeding programmes, is the reintroduction of the offspring into the natural habitat but only if it will provide a chance that a viable population will be established (Pullin, 2002). Captive breeding for the reintroduction back into the wild is mainly used as a partial recovery of declining populations (Grimwood, 1962). This means that captive breeding alone would not work on its own, but only when it is put together with the conservation or reconstruction of a habitat where reintroduction is a possibility. When thinking about releasing captive bred offspring, there is a need for the individual to have learned some survival behaviours as juveniles in order to live successfully once released. These animals should be given the chance to learn this behaviour through a range of training within the captive habitat, so that the probability of survival in the wild would be roughly equal to that of wild animals of the same species (IUCN, 2008). Also there must be a large amount of care taken so that the larger animals (mainly carnivores and other large mammals etc) do not become too confident around humans, as this could cause them to be a danger to the local inhabitants and the local livestock as well as to themselves once in the wild.
Building up numbers for reintroduction
Initial source of stock can endanger remaining small wild populations
Enables research on the biology of species
Facilities in which to do the breeding are needed
Can eventually reduce the need to collect individuals from the wild
Maintaining a large enough population size to prevent problems of genetic drift and loss of variability
Captive colonies can be used to educate the public about the species
Captive populations may undergo selection, adapting them to their captive conditions and leaving hem maladapted to their natural environment
Loss of learned behaviour can occur due to unnatural behaviour under captive conditions
Susceptibility to disease due to artificially high concentration of individuals
It may be difficult to get the species to breed under captive conditions.
Table 1. From Pullin, 2002
Problems with the reintroduction of captive bred species
It has been found that one of the biggest problems for captive breeding and the reintroduction of the offspring into the wild is that sometimes the process has been found to have been too successful. Therefore there is an excess stock of bred offspring ready to be reintroduced but without a location to release them at. This excess stock could be relocated to other zoos to improve their genetic pool or in very few cases there may be the urge to reintroduce this excess stock into the wild even if the habitat and environment isn't up to standards, which could mean that the individuals are more likely to have a shorter life span than if they were reintroduced into a more appropriate habitat (Pullin, 2002). Some of the disadvantages of the reintroduction of captive bred populations have some concerns with the possibility of interbreeding within captivity, the chance that there could be some domestication of the captive population by human impact which could cause issues in the wild, and there is the fear that any offspring of mating captive and wild individuals could lose adaptations to the local environment / habitat (Roldán et al, 2011). Due to the range of these different disadvantages in the reintroduction of captive bred individuals, it is sometimes seen as a last resort when it comes down to trying to increase wild population size. There have been many successful releases of captive bred individuals into the wild (Wilson et al, 2010). But the release programmes have very little monitoring of the species after the release of the captive bred animals, which means that there isn't very much research into the success of the reintroduction process which should be evaluated in order to improve the efficiency of these programmes.
Evidence of captive breeding and reintroduction
One study by Roldán et al (2011) looked into the declining levels of the Greater Rhea (Rhea americana) in wild populations, especially the declining levels found in Central Argentina. The Greater Rhea at the moment is found in the Near Threatened category in the IUCN red list (IUCN, 2008), this is at this level due to the fact that the species levels are going to continue to decrease due to the loss of genetic variability. This is why the release of captive bred populations in to the wild has been seen as a way to increase local wild populations which will also increase the genetic variability. This shows that captive bred populations have a very significant role within reintroduction in to the wild. Roldán et al said that the similarity that has been found between wild and captive populations could be due to three different factors. These factors were: 1. that the short amount of time since farms of the Greater Rhea were established and the adult life expectancy of captive bred individuals released, 2. that the breeding stocks in the wild populations may cause there to be a genetic loss within the population, therefore the captive population could possibly represent a small sample of wild populations, and finally 3. that the artificial selections of individuals have not been seen, which would reduce the possibility of divergences that can be found in allelic frequencies from human intervention. This study showed that there was an importance in keeping rhea farms as way of captive breeding and to then release the offspring into the wild populations in order to increase population size.
Rantanen et al, (2010) looked at the development of anti-predator behaviour and whether or not this behaviour is altered when the individual is subject to captive conditions. This could mean that reintroduced captive bred individuals may not have the same vigilance to predators as the native population and therefore more likely to be vulnerable to predators. Behaviour deficiencies such as this could be a main factor into why some reintroductions have low success rates. Rantanen et al looked at wild and captive bred grey partridges. The captive bred released individuals were observed and the vigilance was looked into both as a group and on an individual scale. They found that overall the released individuals were less vigilant both individually and as part of a group compared to wild individuals. This makes the reintroduced population more at risk of predation and that the wild population will remain small.
In conclusion there is plenty of evidence showing that captive breeding has some major disadvantages into the reintroduction of individuals that have been bred in captivity and the chance that these individuals could possibly have a shorter life span than native wild individuals e.g. the anti-predator behaviour (Rantanen et al, 2010). There are also many studies that show that there is a need for individuals to be bred in captivity and then released into the wild in order to increase the levels of wild populations of a species (Roldán et al, 2011). Overall it is too soon to see if captive breeding reintroduction has a positive long term effect on threatened / endangered species populations, with the Arabian oryx being seen as one of the most successful reintroductions from captivity (Kleiman et al, 1994).
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