Image: The Panamanian golden frog, Credit: Maryland Zoo
Zoos also have a key role in maintaining genetic diversity within certain species, which ultimately acts as a barrier to their extinction. The aim of these programmes is to conserve and retain genetic diversity in a given species, while increasing its breeding population. With higher genetic diversity and a larger population size comes more evolutionary potential, whereby species is more robust and less vulnerable to environmental changes. It is perhaps easier to appreciate the importance of high genetic diversity and population size when we think about what might happen if they are decreased. If a species has a reduced ability to evolve to climatic changes and becomes more susceptible to genetic disorders and inbreeding, it could be at higher risk of extinction.
A common cause of reduced genetic diversity and low population size is when a population undergoes a bottleneck, whereby the number of individuals in the population is drastically reduced in a single event, such as an epidemic, or is more slowly reduced by ongoing stresses such as habitat loss. With a smaller population size, inbreeding is more likely – and this further reduces genetic diversity and reproductive fitness. This in turn reduces survival rates, further reducing the population size, leading to more inbreeding – a cycle known as an extinction vortex. Once in this downward spiral, the species more is likely to face extinction if it is not rescued by the introduction of unrelated individuals with new genetics.
Zoos effectively hold isolated fragmented populations of a species and through translocating individuals to other zoos, they artificially unite the captive populations. To do this, the global zoo network collaborates with the World Conservation Union and different species are assigned a coordinator - for example, ZSL keeps the blue-crowned laughingthrush’s (Garrilax courtoisi) international studbook and creates the breeding plan, involving other zoos worldwide. This conserves genetic diversity and population size to maintain scope for wild reintroduction in order to support wild populations.
One success story is the Amur Leopard. There are just 50-70 Amur Leopards (Panthera pardus orientalis) left in the wild, in a small pocket of Russia, leaving them susceptible to an extinction vortex. They are considered critically endangered on the IUCN’s Red List. But with a further 220 Amur Leopards captive in zoos, the ZSL and Moscow zoo have a breeding plan in place and reintroductions organised. In this way, captive populations can serve to increase genetic diversity and population size for the remaining Amur leopards in the wild and help this magnificent big cat avoid extinction.