Hemiessential resources - when the level of an essential resource declines, the use of a nonessential resource increases. Complementary resources - a small amount of one essential resource can replace a relatively large amount of another essential resource. Antagonistic resources - a small reduction in one resource requires the substitution of a relatively large amount of a second essential resource. These various interactions are illustrated in Figure 20-18 . Resource Synergism Experimental work has demonstrated widespread synergism among resources in their effects on consumers.
Complementary resources can be synergistic in their effects.
Most species play roles as both consumer and resource. Hence, population regulation depends on the complex interactions that occur among organisms and their resources.