Using stable isotopes to quantify species interaction strengths

Honors thesis


Understanding ecological interaction strengths is one of the main objectives of ecology. Recently, two methods for estimating interaction strengths of predator- prey interactions in nature have been proposed: a field observation approach proposed by Novak and Wootton (2008) and stable isotope analysis. The field observation method estimates feeding rates based on feeding observations, handling times and prey abundances. Stable isotope analysis estimates diet proportions using mixing models of ratios of heavy to light carbon and nitrogen isotopes in body tissues of predators and their prey. However, because these two methods are relatively new, few studies have been conducted to understand and contrast their estimates of interaction strengths. I sought to quantify the correlation between the estimates of interaction strength made by the two methods. Both methods were conducted simultaneously in a rocky intertidal community on the Oregon coast with the whelk Nucella ostrina as the focal predator and the barnacle Balanus glandula and the mussel Mytilus trossulus as the two primary prey species. I documented a non-significant and weak correlation between the two method’s estimates of interaction strength. I hypothesize that this lack of correspondence between the methods may be explained by abnormal δ13C enrichment in the whelks compared to their prey, and a lack of variation in observed predator diets between replicate sample populations.

Oregon State University (Honors)
Isaac Shepard
Isaac Shepard
Honors Student