Life in the wild harbours the risk of predation, food shortages, harsh climates, and intense competition. Zoo animals, by contrast, are protected from these dangers. University of Zurich researchers were part of an international team that studied over 50 mammalian species to determine whether the animals live longer in zoos than in the wild.
How long do animals live?
Although the question seems trivial, it is not easy to answer — especially in the case of free-ranging animals, as it is extremely difficult to determine accurate dates of birth and death of all members of a specific population. By comparison, zoos meticulously record the births and deaths of the animals in their care. Now, however, studies of known-aged individuals in the wild are available, making it possible to compare demographic parameters, including longevity.
Smaller species attain greater longevity in zoos
The research team led by the University of Lyon and the University of Zurich assessed the demographic parameters of more than 50 mammalian species. The scientists discovered that longevity was higher at the zoo for more than 80% of the mammals studied — species such as African buffalos, reindeer, zebras, beavers, or lions. The study is published online on 7 November in the journal Scientific Reports.
“All 15 carnivore species in our dataset attained greater longevity at the zoo. It seems that even for predators, life in the wild is not necessarily without its perils,” states Prof Clauss.
The greater longevity at the zoo was particularly prominent among smaller species having a generally shorter lifespan, for instance, tree shrews, weasels, white-tailed deer, or African wild dogs. The juveniles and adults of these species typically fall victim to predators or to intraspecific competition in the wild, thus reducing their average longevity. “With regard to long-lived species that generally have lower mortality rates in the wild, there is less that zoos can protect them from. As such, the effect is not as great and, indeed, in some cases is even reversed,” says Clauss.
Time lag in success measurement
The researchers emphasise that their results reflect historic animal husbandry conditions at zoos and not currently practised conditions. “In order to evaluate longevity of a population, we only consider the ‘extinct cohort’ — that is, a group of individuals born in a certain period, all of which have died. Individuals that are still alive would skew the analysis,” says Dr. Jean-François Lemaître from the University of Lyon and researcher at the Centre National de le Recherché Scientifique (CNRS). This means that changes in the husbandry of long-lived animals introduced in the last decade have not yet influenced the results, as many members of the cohorts affected by these changes are still alive. Whether changes made today influence longevity can therefore only be determined thirty years from now.
Longevity as a single contributing factor cannot support complex ethical judgements on keeping animals the researchers emphasise. “A thorough assessment of the husbandry of a species demands consideration of many other aspects. The most important insight of our study is possibly that it demonstrates that life in the wild is not a life in paradise,” says Prof. Clauss
(Source: Universität Zürich press release, 08.11.2016)