Analysis of Carbon and Nitrogen Stable Isotope Levels in Side-blotched Lizards ( Uta stansburiana ) Fed Varying Diets

When attempting to determine the diet of wild animals, a limited number of techniques currently exist. Often, biologists look at the stomach contents or feces of an animal, if they cannot observe what it is eating directly. However, these techniques often cannot be used with reptiles because they may not eat often or may have an empty stomach when the contents of their stomach are examined. Many ecologists have begun to use stable isotopes of carbon and nitrogen to determine what an animal has eaten. Stable isotopes are useful because unlike radioactive isotopes, stable isotopes do not decay and thus can be used as a better tracer through different trophic levels. Obtaining stable isotopes can be accomplished by analyzing a small tissue sample from the animal and comparing its carbon and nitrogen stable isotope levels to those of several of its potential prey. Since variation in carbon and nitrogen isotopes exists in all living things and is maintained with increases in trophic level, these chemical signatures can be good indicators of an animal’s current diet. Our central question is to test the assumption that there is a direct correlation between the stable isotope signatures found in Side-blotched Lizards (​Uta stansburiana​) and some of their insect prey in the lab, where we could control their diet. We predicted that there would be a direct correlation between the carbon (δ​C) and nitrogen (δ​N) levels of the lizards and those of their prey. We found that, although​ ​δ​C and δ​N values of lizards generally matched their diet, diet complexity did not significantly alter lizard toe tissue stable isotope ratios. This method has the potential to be more effective at determining wild reptile diet than other techniques currently used.