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Journal article
Does a lack of juveniles indicate a threat? Understanding body size distributions in a group of long-lived vertebrates
The Journal of animal ecology, Early View
2025
PMID: 40727957
Abstract
Turtles are declining globally, and absences of juveniles during surveys are often interpreted as evidence of threats to early life stages. In Australia, for example, it is widely argued that a low number of juveniles is likely due to nest predation by introduced red foxes (Vulpes vulpes). However, small sample sizes within populations, low detectability of juveniles and turtles' long lifespans often confound the conclusion that a paucity of juveniles indicates a declining population. Because turtles have long reproductive lifespans, we might intuitively expect most turtle populations to be heavily weighted towards large individuals, but a ‘typical’ or ‘healthy’ size distribution for turtle populations has not been well established.
Therefore, we collated data on 41,021 freshwater turtles from 38 species and 428 populations located in parts of Australia both with and without introduced foxes, as well as populations in the United States of America, which naturally have raccoons (Procyon lotor), foxes and other nest predators. We examined population-level body size distributions to establish a baseline for ‘typical’ turtle populations and test whether populations that are exposed to introduced foxes have proportionately fewer juveniles compared to both AU populations that lack introduced foxes and USA populations that are naturally exposed to nest predators.
We found that most turtle populations in AU and the United States were heavily skewed towards adults and had few juveniles, regardless of the presence of foxes or other nest predators. There were, however, clear differences among population survey methods: those that target shallow areas (e.g. crawfish traps) tended to capture proportionately more juveniles, and small sample sizes (∼<50) often produced inaccurate representations of size distributions. Additionally, we used a simulation to demonstrate that, given common turtle life history parameters, even stable populations should generally have low proportions of juveniles.
Based on our results, we encourage caution when interpreting turtle size distributions. A small number of juveniles does not inherently suggest that a population is declining due to high egg and/or juvenile mortality, and researchers should pay careful attention to the biases in their methods and strive to capture a minimum of 50–100 turtles before drawing inferences.
Details
- Title
- Does a lack of juveniles indicate a threat? Understanding body size distributions in a group of long-lived vertebrates
- Authors/Creators
- Donald T. McKnight - La Trobe UniversityDeborah S. Bower - University of New EnglandEllen Ariel - James Cook UniversityStephen Beatty - Murdoch University, Centre for Sustainable Aquatic EcosystemsSimon Clulow - University of CanberraMarilyn Connell - Landcare AustraliaAnnette R. Deppe - Univ New England, Sch Environm & Rural Sci, Armidale, NSW, AustraliaSean Doody - University of South Florida St. PetersburgAlastair Freeman - Aquat Species Program, Dept Environm & Sci, Wildlife & Threatened Species Operat, Atherton, Qld, AustraliaArthur Georges - University of CanberraSamantha L. Hannabass - USFWS, Oklahoma Fish & Wildlife Conservat Off, Tishomingo, OK USAEthan C. Hollender - University of Arkansas at FayettevilleHunter Howell - The Wildlife SocietyAaron Krochmal - Washington Coll, Dept Biol, Chestertown, MD USADay B. Ligon - Southeast Missouri State UniversityEric Munscher - SWCA Environm Consultants, Houston, TX USAEric J. Nordberg - University of New EnglandTimothy C. Roth - Franklin & Marshall CollegeAnthony Santoro - Murdoch University, Harry Butler InstituteAngela Simms - La Trobe UniversityJason Schaffer - James Cook UniversityRicky-John Spencer - Western Sydney UniversityPaul Stone - University of Central OklahomaKameron C. Voves - Missouri State Univ, Dept Biol, Springfield, MO USAAndrew D. Walde - Turtle Survival Alliance, N Charleston, SC USASkye Wassens - Charles Sturt Univ, Sch Agr Environm & Vet Sci, Thurgoona, NSW, AustraliaMichael A. Welsh - ACTNick S. Whiterod - Goyder Institute for Water ResearchWytamma Wirth - The University of MelbourneJames U. Van Dyke - Albury Wodonga Health
- Publication Details
- The Journal of animal ecology, Early View
- Publisher
- John Wiley & Sons Ltd on behalf of British Ecological Society.
- Number of pages
- 21
- Grant note
- Commonwealth Environmental Water Office LP200200884 / ARC Linkage; Australian Research Council Arizona Game & Fish Department, Commonwealth Environmental Water Office, Department of Florida Fish and Wildlife, Felburn Foundation New Mexico Department of Game and Fish, Office of Biological and Environmental Research Oklahoma Department of Wildlife Conservation, Texas Parks and Wildlife Department, Turtle Survival Alliance, United States Forest Service, University of New England Faculty of Science, Agriculture, Business and Law Murdoch University AEC WISP15327814; 2829; 3440; 3570; 3660; SL1022308; OEH: SL100441; Forestry 181502; WITK03617606; A19028 / Winton Wetlands, Wodonga Council, Greening Australia and North East Water DEB-74-070631; DEB-79-06301; BSR-84-00861; BSR-90-1977 / Jane Fenwick Foundation AEC19-081; AEC 14-116 / Department of Environment and Science Queensland Government 25 Licence FO25000094-3; BA27000339 / Tiverton Agricultural Impact Fund
- Identifiers
- 991005807943907891
- Copyright
- © 2025 The Author(s).
- Murdoch Affiliation
- Harry Butler Institute; Centre for Sustainable Aquatic Ecosystems
- Language
- English
- Resource Type
- Journal article
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