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Effects of captivity on species

It is common to use captive bred animals for reintroductions; they can be used as a buffer if the natural population goes extinct in the wild. However there are certain drawbacks in using this technique, for instance problems with genetic deterioration, behavioral disorders or other changes in captive bred species attributes. According to Araki et. al. (2007) the effects of captivity on species are in general a 40% decline in fitness/generation. The reasons for this are mainly due to genetic deterioration and behavioral disorders.
 
Some species may have to spend 100-200 years in captivity before their natural habitat is restored, making it hard to get a successful reintroduction. The general optimal time spent in captivity is 10-20 generations according to Robert (2009) and Theodorou & Couvet (2004).

Changes in the food web structure caused by species loss

During the time a species spend in captivity it is not only its traits that change, the ecosystem in which it once lived may also undergo significant changes that can affect the reintroduction success. When a species goes extinct, the ecosystem does not just stay the way it was, it can react differently depending on what place and function the extinct species had in the community. In worst case scenarios there is a risk for the whole ecosystem to collapse, due to trophic cascade effects caused by the extinction of one species whereas in other cases there is a few secondary extinctions or none at al.

The strength of the link between species is essential when it comes to how other parts of an ecosystem react to extinctions. The link-strength is not the only vital parameter if species are removed from an ecosystem, for example species richness and connectance is vital when it comes to the robustness of a food-web. For example, if there are few connections between species in a food-web, the chances of secondary extinctions are much higher compared with ecosystems with many connections.

Christanou & Ebenman (2006) list four possible different outcomes when a species is reintroduced into a food-web;

Fig 1. Four potential outcomes of a species reintroduction I) The system or the species itself has changed too much for the reintroduced species to survive in the system, II) The reintroduced specie can survive for a while but cause secondary extinctions and in the end goes extinct itself. III) The system and the reintroduced species have not changed significantly from the initial deletion causing success without any secondary extinctions. IV) The reintroduced species is strong enough to survive and compete out other species in the food-web causing secondary extinctions (from Christanou & Ebenman 2006).

Effects of a reintroduction

Not only can the loss of a species affect the food-web, but also the reintroduction can cause further damage and secondary extinctions, especially if there were secondary extinctions when the species initially disappeared. Laikre et. al. (2010, p. 520) lists four additional risks with reintroducing a captive bred species back into the wild: (I) loss of genetic variation, (II) loss of adaptations, (III) change of population composition and (IV) change of population structure. They further state that these risks are largely neglected today, especially in the commercial markets such as the hunting, foresting or fishing industry where enormous amounts of animals are released and plants set out each year.

The effects on food-webs when a captive bred species is reintroduced have not yet been studied to any further extent. Studies have been conducted on the success-rate of reintroduction, reintroduced species born in captivity and their chances of success. Since we know that the invasion of alien species can alter the whole structure of a food-web it is also important to see how the food-web reacts to a reintroduction of a species with changed attributes due to the time spent in captivity.


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Last updated: 05/26/11