Stable carbon and nitrogen isotope discrimination and turnover in a small-bodied insectivorous lizard

ABSTRACT

Laboratory experiments are useful for estimating the carbon and nitrogen isotope discrimination factors and turnover rates that are critical for drawing field-based inferences on consumer diets using stable isotopes. Although the utility of these discrimination factors is widely recognized, work in terrestrial systems has largely been limited to studies involving mammals and birds. In contrast, scant attention has been paid to the application of isotopic techniques to reptiles, despite their broad diversity in terms of numbers of species as well as their trophic roles. Here we estimate carbon and nitrogen isotope discrimination factors and turnover for the tree lizard (Urosaurus ornatus) using a diet-switch experiment. Lizards were collected from a C₄-dominated grassland and then switched to C₃-based diet (crickets) in the laboratory. We estimated discrimination by lizard claw tissue as Δ¹³C = 1.2 ± 0.1 ‰ for carbon and Δ¹⁵N = 0.7 ± 0.1 ‰ (mean ± 1 SE) for nitrogen, with 95 % turnover occurring after ∼15.5 days. These estimates should be appropriate for use in trophic studies of U. ornatus, and possibly other related small-bodied insectivorous lizards.

KEYWORDS:

• Animals
• carbon-13
• diet switch
• isotope ecology
• nitrogen-15
• reptiles
• tissue
• trophic ecology

Acknowledgements

All work was conducted under Arizona state permit (#SP792912) to DBM and approved by Ohio University's Institutional Animal Care and Use Committee (#R06-07). Linda Kennedy and Christine Haas of the Appleton-Whittell Research Ranch of the National Audubon Society provided assistance with field site selection. Natalie Boydston and Aaron Cranford provided field and laboratory assistance. Finally, Kelly Williams, Vincent R. Farallo, Robin Warne, Don Phillips, and three anonymous reviewers provided useful comments on earlier permutations of this manuscript.

Additional information

Funding

This work was funded by an Ohio University Original Work Grant, an OU Research Challenge Grant, and an Ariel Appleton Research Fellowship.