Exploitative competition indirect competition through mutual effects on shared resources
Interference Competition direct competition in which competitors aggressively defend resources—there may be a fine line between the two kinds of competition
Allelopathy chemical competition in terrestrial plants
Consumers can influence competition outcomes
If consumers feed upon a particular species, they can create room for other species that use the same resources as their prey to take hold
Apparent competition may resemble exploitative or interference competition, but in fact represents another factor. Examples include: sage shrubs giving shelter to herbivores on grass, native populations not being able to tolerate introduced pathogens, and the example I know best-garlic mustard, which not only uses allelopathy on other plants, but is not often eaten by deer or any other herbivores.