ABSTRACT
A story from eighteenth-century North America provides an almost trivial example of what trait-mediated indirect interactions are. In rural North America, before massive industrialization, it was a commonplace situation that young boys were excused from classes for the purpose of "scaring crows". Mediating the indirect effect of human on maize through a change in the behavior of the pest contrasts with the density-mediated indirect effect and is thus referred to as a trait-mediated indirect effect. A well-known issue in the intercropping literature is, in the end, a perfect example of the distinction between trait-mediated and density-mediated indirect effects. An example from the author's work in the coffee agroecosystem illustrates how these trait-mediated effects can become quite complicated, and reinforces the notion that they may indeed be more important than the direct effects. Adding the trait-mediated effect to the elementary graph produces a "hypergraph".
