There are four major types of interactions that encompass the most critical and sig­ nificant interactions among and between animals and plants. They are competition, mutualism, herbivore-plant interactions, and predator-prey interactions. Over the last several decades these types of interactions have come under severe scrutiny. The importance of, and in some cases the very definition of and assumptions about, com­ petition, mutualism, and herbivore-plant interactions have changed dramatically. Only recently has the role of predation, as a force shaping the behavior. ecology, and evo­ lution of vertebrate and invertebrate species, been exposed to a similarly intense scrutiny. For example, only recently have researchers experimentally shown that in numerous systems predators are important not only because they eat prey species, but also because they may trigger morphological, behavioral, and life-history changes in prey species.