Food Webs & Environmental Disturbance: What's the Connection?

Abstract

When discussing ecology and environmental awareness, we frequently tell our students that all are mutually dependent and that if one element of an environment is disturbed, there are many, often farreaching consequences for all organisms within that environment. That said, we quickly move on to another topic, thinking that we have increased our students' knowledge about their environment and factors affecting environmental change. We can better help our students understand the interrelatedness of if we can help them to see why are interdependent. Charles Elton (1927), a pioneering animal ecologist, suggests that the structure and activities of animal communities primarily depend on food supply. McInerney (1993) concurs, noting that in nature everyone is someone else's dinner (p. 293). These remarks suggest that all are part of an intricate food and survival chain in which they obtain necessary nutrients directly or indirectly from other (Goodwin 1992). The movement of nutrients and energy among and the resulting interactions are typically represented by food chains or webs (Krebs 1988; Ricklefs 1990; Smith 1980). The structure of a food web is based on the functional relationship of three groups of organisms: autotrophs, heterotrophs and decomposers (which are really heterotrophs but are given their own category because of their nutrient recycling role). Each of these groups relies, directly or indirectly, on the others for attaining their essential nutrients and energy. Even though the movement of nutrients and energy between any two depends on one eating the other, the overall flow pattern for each within the food web is fundamentally different. Nutrients can cycle through the food web an infinite number of times, whereas energy can only flow through the web once (or in some cases, with minimal cycling among the heterotrophs). We often teach the concepts of food chains and webs using lectures supplemented with various diagrams showing the simplicity and/or complexity of various food webs. Students in these situations often fail to see the dynamic interactions among the that make up the food web, as well as the impact of environmental disturbances on the organisms in the food web. Teaching food webs is a perfect opportunity to supplement student learning with student doing. The activity we describe is one that can be used to teach the dynamic nature of food webs and to demonstrate the impact of environmental disturbances on the within a food web to students of all ages. By having students become a member of a food web and actually seek its nutrients from the other living things around it, the students model the behaviors they and other display on a daily basis. The result of this activity is a greater understanding of and appreciation for the interdependencies of things.