As with other sciences, ecology is often initially approached by students as a collection of disparate phenomena and abstract models derived from the natural world. This approach, often correlated with a detail-oriented attempt to memorize numerous facts and reproduce them when required, nonetheless makes it difficult for students to perceive the fundamental relatedness of all ecological models. In contrast, ecologists reason in a very principled way about ecology, even when they don’t explicitly invoke basic principles. Conservation of matter and energy (plus degradation of energy) and the continuity of genetic information are especially powerful for understanding ecology, as is the arrangement of phenomena in a hierarchy of spatial and temporal scales. A firm grasp of the ways in which these principles interact will greatly help students to be successful in reasoning ecologically in their adult lives, especially for those who don’t pursue further studies in ecology. Using items designed for both written and interview assessments, we investigated students’ use of principles in their reasoning about ecology, both before and after instruction designed to foreground these principles. The students in this study were enrolled in an introductory ecology course at a large public research university, and were primarily science majors.

Results/Conclusions

Students did demonstrate an increased awareness and recognition of the principles by the end of the course, although their ability to apply them in new situations or recognize them in unfamiliar contexts did not improve nearly as much. Students were also often drawn to rationales for phenomena that were based on unprincipled, everyday reasoning rather than the correct scientific principles. For instance, in a question about the movement of matter and energy through ecosystems, only 18% of students answered correctly on the pre-test (matter cycles, energy flows due to entropic heat loss), while 39% of the post-test students could do so. Many students, though, struggled to describe conservation of matter and energy on extensions to this question. Beyond nutrient cycles, which had been discussed near the time of post-testing, most respondents didn’t cite other applications of this principle. Similarly, questions about genetics and selection were often answered correctly if the principle of genetic continuity was apparent, but very often incorrectly in situations where the students needed to apply that principle. Thus, we found that repeatedly drawing students’ attention to several key principles did increase their awareness of these concepts, but synthesizing and applying these principles remained difficult for many students.