Using light stable isotopes to assess stream food web ecology in a general ecology laboratory course

ABSTRACT

Stable isotopes in natural materials provide a powerful way to study energy flow in many systems and are widely used in fields such as archaeology, ecology, forensics, geochemistry, geology, oceanography, palaeoecology and palaeoclimatology. Based on the manner in which stable isotopes fractionate in natural systems, they allow scientists to address a wide array of research topics ranging from tracking climatic shifts, ascertaining organisms’ migratory patterns, matching organisms to their diets and/or environments, assessing food web bioenergetics, documenting ecosystem changes through time, measuring soil carbon budgets and soil microbial activity, etc. Hence, it may be a viable option to use stable isotopes to investigate stream and food web ecology with students. Students with no prior experience working with stable isotopes successfully met learning objectives by completing the requisite field and laboratory protocols, analysing data, interpreting results, and communicating their findings in a report modelled after a peer-reviewed scientific journal article. While this activity focused on food web ecology in a stream ecosystem, the method is repeatable, cost-effective, and can be modified relatively easily to evaluate food webs in virtually any other ecosystem.

KEYWORDS:

• Active learning
• community ecology
• experiential learning
• δ¹³C
• δ¹⁵N
• light stable isotopes

Acknowledgments

We thank Kevin Alexander for sharing knowledge of aquatic invertebrates in the Taylor River, Holly Brunkal for sharing knowledge of Taylor River geology, Jacqueline Galang for testing the introductory and advanced R exercises and providing feedback, Justin Conover for reviewing earlier versions of R code, Miles Perry for information technology support, Kayla Wernsing for assisting with isotope sample processing in the ISU SIPERG lab, and Nocona Swindell for assisting with student instruction in the field and laboratory at WCU. We also thank the students of Biology 302 at Western Colorado University for their enthusiastic participation in this exercise. We are grateful to Lynn Clark and two anonymous reviewers for comments which improved the quality of the manuscript. This work was funded entirely by student course fees; no outside funding was obtained.

Disclosure statement

No potential conflict of interest was reported by the authors.

Data accessibility statement

The field sampling methods handout provided to students (Supplemental File 1), laboratory methods handout provided to students (Supplemental File 2), introductory and advanced R tutorials (Supplemental Files 3 and 4, respectively), instructor keys (Supplemental Files 3Key and 4Key, respectively), materials list and budget (Supplemental File 5), a software helpfile for instructors (Supplemental File 6), and a spreadsheet of raw data used in this exercise in Microsoft Excel format (Supplemental File 7 [2019_EA_Houston_class project.xlsx]; See also Table 2) are available via public GitHub repository: https://github.com/hannahcarroll/Aquatic-isotopes-public

Educators who wish to teach these analyses without conducting the field work and laboratory sample preparation may use the materials as provided for their own courses. This may be particularly useful at institutions where the costs may be prohibitive.

Supplementary Material

Supplemental data for this article can be accessed here.