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Most mam­mals have a greater life expectancy in zoos

pub­lished 07 Novem­ber 2016 | mod­i­fied 27 Decem­ber 2016

African lioness at Odense ZooLife 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.

The most impor­tant insight of our study is pos­si­bly that it demon­strates that life in the wild is not a life in paradise
Mar­cus Clauss, pro­fes­sor of nutri­tion and biol­ogy of zoo and wild ani­mals, Uni­ver­sity of Zurich »

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.

zoo animals life expectancyGraph­i­cal dis­plays of the met­rics of sur­vival and actu­ar­ial senes­cence ana­lyzed in this study

Data from female lions (Pan­thera leo) in zoo (in brown) and free-​ranging (in green) con­di­tions are used for illus­tra­tive pur­poses. Female lions in the zoo pop­u­la­tion live longer (age in years) and have a lower base­line annual mor­tal­ity (in log%), a later onset of senes­cence (in years) and a lower rate of actu­ar­ial senes­cence (mea­sured as the expo­nen­tial rate of mor­tal­ity increase per year).
Credit: Tidière et al.,2016. Com­par­a­tive analy­ses of longevity and senes­cence reveal vari­able sur­vival ben­e­fits of liv­ing in zoos across mam­mals. Sci­en­tific Reports, doi:10.1038/srep36361.

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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.

Zoo ethics
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)

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