Prey-switching does not protect a generalist turtle from bioenergetic consequences when its preferred food is scarce

Kristen Petrov, Ricky-John Spencer, Natasha Malkiewicz, Jessica Lewis, Claudia Keitel, James U. Van Dyke

Research output: Contribution to journalArticlepeer-review

10 Citations (Scopus)

Abstract

Background Optimal foraging theory explains how animals make foraging decisions based on the availability, nutritional content, and handling times of different food types. Generalists solve this problem by consuming a variety of food types, and alter their diets with relative ease. Specialists eat few food types, and may starve if those food types are not available. We integrated stable isotope analyses with previously-published stomach contents and environmental data to investigate how the foraging ecologies of three sympatric freshwater turtle species vary across four wetlands that differ in turbidity and primary producer abundance. Results We found that the generalist Emydura macquarii consumes a varied diet (but mostly filamentous green algae) when primary producers are available and water is clear, but switches to a more carnivorous diet when the water is turbid and primary producers are scarce, following the predictions of optimal foraging theory. In contrast, two more-specialized carnivorous species, Chelodina expansa and Chelodina longicollis, do not differ in diet across wetlands, and interspecific competition may increase where E. macquarii is carnivorous. When forced to be more carnivorous, E. macquarii exhibits higher rates of empty stomachs, and female turtles have reduced body condition, but neither Chelodina species are affected. Conclusions Our results provide support for optimal foraging theory, but also show that the ability to change diet does not protect the generalist from experiencing lower foraging success when its preferred food is rare, with direct consequences for their energy budgets. Our results have conservation implications because wetlands in the Murray–Darling river system are increasingly turbid and have low macrophyte abundance, and all three species are declining.
Original languageEnglish
Article number11
Number of pages12
JournalBMC Ecology
Volume20
Issue number1
DOIs
Publication statusPublished - 2020

Open Access - Access Right Statement

© The Author(s) 2020. This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons .org/licenses/by/4.0/. The Creative Commons Public Domain Dedication waiver (http://crea ivecommons .org/publicdomain/ zero/1.0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data.

Keywords

  • food webs
  • stable isotopes
  • turtles

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