There are usually smaller numbers of carnivores than there are of herbivores in a community; the number of top carnivores (animals that have no predators other than man) in any area may be very small indeed. A pyramid of numbers may be said to exist.

In a woodland habitat in summer, there are usually countless thousands of caterpillars and other small insects living on the leaves of trees and other plants. These creatures are eaten by small birds such as titmice and warblers, of which there may be several pairs to each hectare (2.47 acres) of woodland. Small birds form one of the sources of food of the sparrow hawk (the top carnivore) but there is normally only one pair of these birds of prey in quite a large area of woodland.

As the creatures that are high in the pyramid have to search a larger area for their food than those lower down they tend to be larger. Thus a ladybird is larger than the aphids (small plant-eating insects such as greenfly) on which it feeds, and a predatory mammal such as a stoat or weasel is several times the size of the field-mice and bank voles which it hunts.