Facing Truths About Population Management

Even without considering genetic diversity, managing zoo populations sustainably without applying controlled mortality faces a predictable dilemma: Holding space is limited, and zoos worth their salt will inevitably become better at reducing accidental (uncontrolled) mortality. For most species, longevity attainable under good husbandry conditions is considerably longer than generation time, and even though most animals can reproduce until death, there is reproductive senescence, where the probability of successful reproduction decreases with age. Thus, over time, available holding space will inevitably be filled by older animals of lower fecundity. Breeding recommendations that aim at exact numerical replacement to avoid surplus at all cost rather than accounting for average success rates (so that the number of offspring will overshoot the target by up to 50% of the time) will stochastically lead to declines in population size. For small populations, extinction in zoos thus predictably becomes a matter of time. Only large populations will be able to exist at high proportions of old animals, with waves of replacement cycles. Therefore, gaining public acceptance for respectful and humane controlled mortality is essential for the long-term sustainability of small zoo populations. Concepts of continuously increasing holding capacities, using frozen gametes to generate offspring when needed, or nonspecific hopes that compassionate conservation will align individual longevity and conservation goals, detract from the necessity to act. Details of welfare and education can support the call for controlled mortality, but it is the inevitability of the outlined process that obliges us to choose honestly between being empathetic observers of extinction or taking responsibility to conserve animal species.

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Publication Details

Journal
Zoo Biology
Published
2026-08-20
DOI
https://doi.org/10.1002/zoo.70099
Primary Topic
Animal Behavior and Welfare Studies
Type
article
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article

Facing Truths About Population Management

Imke Lüeders, Therese Hård, Adam Eyres, Miguel Casares et al.
Zoo Biology
Animal Behavior and Welfare Studies
article

Facing Truths About Population Management

Imke Lüeders, Therese Hård, Adam Eyres, Miguel Casares, Emile F. Prins, Brian Zimmerman, Jörg Beckmann, Stefan Hoby, Guido Westhoff, Anita Burkevica, C Wenker, Severin Dressen, José Kok, Jacques Kaandorp, Hanspeter W. Steinmetz, Chris Walzer, Julia Stagegaard, Chrispijn M. Schilp, Marco Roller, Arne Lawrenz, Bjarne Klausen, Karin Federer, Cyriel Ververs, Andrew J. Abraham, Marcus Clauß, Lara Scherer, Laurie Bingaman Lackey, Jan Pluháček, Mads Bertelsen, Sven Hammer, Richard Gibson, Sébastien Laurent, Mark Snowball, Job B. G. Stumpel, João Pedro Meireles, Baptiste Mulot, Sandra Reichler-Danielowski, Zjef Pereboom, Dennis W. H. Müller, Christine M. Kaandorp‐Huber, Tobias Knauf‐Witzens, Tim F. Schikora, Felix V. Husemann, Pascal Marty, Rolf‐Arne Ølberg, Theo B. Pagel, Maya S. Kummrow, Douglas Richardson, Sabrina Linn
article en

Abstract

Even without considering genetic diversity, managing zoo populations sustainably without applying controlled mortality faces a predictable dilemma: Holding space is limited, and zoos worth their salt will inevitably become better at reducing accidental (uncontrolled) mortality. For most species, longevity attainable under good husbandry conditions is considerably longer than generation time, and even though most animals can reproduce until death, there is reproductive senescence, where the probability of successful reproduction decreases with age. Thus, over time, available holding space will inevitably be filled by older animals of lower fecundity. Breeding recommendations that aim at exact numerical replacement to avoid surplus at all cost rather than accounting for average success rates (so that the number of offspring will overshoot the target by up to 50% of the time) will stochastically lead to declines in population size. For small populations, extinction in zoos thus predictably becomes a matter of time. Only large populations will be able to exist at high proportions of old animals, with waves of replacement cycles. Therefore, gaining public acceptance for respectful and humane controlled mortality is essential for the long-term sustainability of small zoo populations. Concepts of continuously increasing holding capacities, using frozen gametes to generate offspring when needed, or nonspecific hopes that compassionate conservation will align individual longevity and conservation goals, detract from the necessity to act. Details of welfare and education can support the call for controlled mortality, but it is the inevitability of the outlined process that obliges us to choose honestly between being empathetic observers of extinction or taking responsibility to conserve animal species.

Zoo Biology
Karlsruhe Institute of Technology (DE), University of Hohenheim (DE), Royal Zoological Society of Scotland (GB), University of Bern (CH), Zoological Society of London (GB), Wildlife Conservation Society (US), Texas Parks and Wildlife Department (US), University of Veterinary Medicine Vienna (AT), University of Auckland (NZ), Kema International (Netherlands) (NL), University of Wuppertal (DE), University of Cologne (DE), University of Basel (CH), University of Ostrava (CZ), University of Zurich (CH), Wuppertal Institute for Climate, Environment and Energy (DE), Cheetah Conservation Fund (NA), Association of Zoos and Aquariums (US), Codarts Rotterdam (NL), Odense Municipality (DK), Copenhagen Zoo (DK), Gentofte Hospital (DK), World Association of Zoos and Aquariums (CH), Swedish University of Agricultural Sciences (SE), Eskilstuna Municipality (SE), Hunter College (US), Auckland University of Technology (NZ), Hochschule Bremerhaven (DE), Moravská Vysoká Skola Olomouc (CZ), Klinikum Görlitz (DE), Schwyz University of Teacher Education (CH), Halle Zoo (DE), Royal Zoological Society of Antwerp (BE), Nuremberg Hospital (DE), Georg Simon Ohm University of Applied Sciences Nuremberg (DE), Helios Hospital Schwerin (DE), Kruse Smith (Norway) (NO), University Hospital Olomouc (CZ), Treant Zorggroep (NL), Heidelberg Engineering (Germany) (DE), Établissement Français du Sang (FR), Zoos Victoria (AU), Zürich Zoological Garden (CH), Rheinmetall (Switzerland) (CH), J.M. Burgerscentrum (NL), Bavarian State Collection of Zoology (DE), Klinikum Bremerhaven-Reinkenheide (DE), Senckenberg Museum für Naturkunde Görlitz (DE), GlaxoSmithKline (Germany) (DE), Klinikum Rheine (DE), Technology Transfer Center Bremerhaven (DE), 's Heeren Loo (NL), Center for Rheumatology (US), Zata Pharmaceuticals (United States) (US), 21c Consultancy (United Kingdom) (GB), Auckland Zoo (NZ), Frankfurt Zoological Society (DE), Rotterdam University of Applied Sciences (NL)
Life in Land
Openalex Percentile: Top 9%
Animal Behavior and Welfare Studies
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