Practice question

Diffuse coevolution occurs when evolutionary change in one species is shaped by interactions with a group of species, and reciprocal selection is likewise distributed across that ecological network. A plant may evolve chemical defenses in response to several herbivores, while each herbivore also encounters many host plants and natural enemies. No single pair alone explains the resulting traits. This differs from a tightly coupled pairwise arms race, such as highly specific host–parasite interactions, in which reciprocal selection can be attributed mainly to two partners. Multiple interactions may reinforce one another, oppose one another, or vary geographically, producing selection mosaics. Competition can certainly participate; it does not disappear in diffuse systems. Nor does only one species evolve, because coevolution requires reciprocal evolutionary responses, although the strength and timing need not be symmetrical. Demonstrating diffuse coevolution requires evidence that community composition changes selection on traits, not merely that many species coexist. The concept therefore links network ecology with evolutionary dynamics across several interacting lineages.