Primary consumer: consumers of primary producers; herbivores from ants to zebras. Tertiary consumers: carnivores who eat secondary consumers. Emphasizes the influence of populations on growth rates in other populations. Beetle here are keystone consumers because when they are removed, the edifice of the community tumbles. Suggested that the earth is green because carnivores depress the populations of herbivores that would otherwise consume most of the vegetation. Indirect effect: one trophic level exerts influences on a send by affecting a third: cascades involves effect that alternate across trophic levels. (2005) Top-down control: when higher trophic levels determine the sizes of the trophic levels below them. Bottom-up control: when the size of a trophic level is determined by the rate of production of its food resource. The presence of fish in a pond reduced the abundance of dragonfly larvae, which reduced the abundance of dragonfly adults, and thereby increased the abundance of pollinators and the number of seed produces by nearby plants.