Determination of population age structure from the survivorship of individuals of unknown ages in unicorns and platypuses

J. W. Macgregor; P. A. Fleming; O. Wade; R. Donaldson; K. S. Warren

doi:10.1071/ZO24027

RESEARCH ARTICLE (Open Access)

Previous Contents Vol 73(3)

Determination of population age structure from the survivorship of individuals of unknown ages in unicorns and platypuses

J. W. Macgregor

^A ^B ^* , P. A. Fleming

^C , O. Wade ^B , R. Donaldson ^B and K. S. Warren ^B ^D

+ Author Affiliations

- Author Affiliations

^A Ulverstone Veterinary Clinic, UVC Wild, 54 Alexandra Road, Ulverstone, Tas, Australia.

^B Murdoch University School of Veterinary Medicine, Conservation Medicine Program, Murdoch, WA, Australia.

^C Murdoch University Harry Butler Institute, Environmental Science and Conservation Biology, Murdoch, WA, Australia.

^D Murdoch University Harry Butler Institute, Centre for Terrestrial Ecosystem Science and Sustainability, Murdoch, WA, Australia.

^* Correspondence to: platypusproject@hotmail.com

Handling Editor: Brad Law

Australian Journal of Zoology 73, ZO24027 https://doi.org/10.1071/ZO24027

Submitted: 28 September 2024 Accepted: 7 March 2025 Published: 28 March 2025

© 2025 The Author(s) (or their employer(s)). Published by CSIRO Publishing. This is an open access article distributed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND)

Abstract

Population age structure is an important parameter for wildlife population modelling. However, for many species it is not possible to accurately assess the age of adult individuals. We present a hypothetical example to illustrate a previously described method of determining population age structure from the survivorship of individuals of unknown ages that to our knowledge is unused in the fields of zoology and ecology. We then apply this method to data collected over 10 years for a population of wild platypuses (Ornithorhynchus anatinus), a species whose adult individuals cannot be accurately aged and for which only limited data on life history characteristics are available. Our results show a lower mortality rate over the first years of life of platypuses than the one previous study available for comparison, and suggested a Type I or Type III survivorship curve.

Keywords: cohort survivorship curve, life history, longevity, modelling, platypus, population age structure, stationary populations, survivorship.

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