The adequacy of aging techniques in vertebrates for rapid estimation of population mortality rates from age distributions

Abstract

As a key parameter in population dynamics, mortality rates are frequently estimated using mark–recapture data, which requires extensive, long‐term data sets. As a potential rapid alternative, we can measure variables correlated to age, allowing the compilation of population age distributions, from which mortality rates can be derived. However, most studies employing such techniques have ignored their inherent inaccuracy and have thereby failed to provide reliable mortality estimates. In this study, we present a general statistical model linking birth rate, mortality rate, and population age distributions. We next assessed the reliability and data needs (i.e., sample size) for estimating mortality rate of eight different aging techniques. The results revealed that for half of the aging techniques, correlations with age varied considerably, translating into highly variable accuracies when used to estimate mortality rate from age distributions. Telomere length is generally not sufficiently correlated to age to provide reliable mortality rate estimates. DNA methylation, signal‐joint T‐cell recombination excision circle (sjTREC), and racemization are generally more promising techniques to ultimately estimate mortality rate, if a sufficiently high sample size is available. Otolith ring counts, otolithometry, and age‐length keys in fish, and skeletochronology in reptiles, mammals, and amphibians, outperformed all other aging techniques and generated relatively accurate mortality rate estimation with a sample size that can be feasibly obtained. Provided the method chosen is minimizing and estimating the error in age estimation, it is possible to accurately estimate mortality rates from age distributions. The method therewith has the potential to estimate a critical, population dynamic parameter to inform conservation efforts within a limited time frame as opposed to mark–recapture analyses.

Age structure of a lizard along an elevational gradient reveals nonlinear lifespan patterns with altitude

“…The age of the lizards was determined by phalanx skeletochronology ( Comas et al. 2016 ), which is one of the most accurate age estimation techniques in animals ( Zhao et al. 2019 ).…”

Climate change and ageing in ectotherms

“…To this end, knowing the age of individuals is helpful in studies in the wild. In temperate vertebrate ectotherms, growth shows seasonal variation and age can be determined through skeletochronology, for example, by counting lines of arrested growth in reptiles and amphibians, growth rings in fish scales or bands in fish otoliths (Zhao, Klaassen, Lisovski, & Klaassen, 2019).…”

A cost‐effective blood DNA methylation‐based age estimation method in domestic cats, Tsushima leopard cats (Prionailurus bengalensis euptilurus) and Panthera species, using targeted bisulphite sequencing and machine learning models

“…Age information is important for both ex situ and in situ wildlife conservation, as it is relevant to individual behaviour, health, reproductive capacity and mortality (Blomqvist & Sten, 1982; Kirkwood & Austad, 2000; Nussey et al., 2013; Youn et al., 2022; Zhao et al., 2019). Age estimation can help determine demographic characteristics and predict current and future extinction risks for wildlife populations (Lacy, 2019; Oli & Dobson, 2003).…”