A consumer-resource interaction occurs when one organism obtains energy or nutrients by consuming another organism or part of it.

In predation, a predator kills and consumes prey. In herbivory, an animal consumes plant or algal tissue, often without killing the entire organism.

These interactions affect both populations. Increasing prey abundance can provide more food for predators, increasing predator survival or reproduction. Increasing predator abundance can raise prey mortality. This feedback can produce coupled fluctuations rather than independent population trajectories.

Predation also changes community composition by altering which species are abundant enough to compete with others.

Prey and plants can possess defenses such as armor, toxins, camouflage or escape behavior, while consumers differ in their ability to detect, tolerate or capture defended resources. These traits can strongly modify the demographic effect of the interaction.

A common mistake is to assume that predators always reduce prey to the lowest possible abundance. Predator populations depend on their resources, and prey can become harder to find when rare. Environmental refuges, alternative prey, seasonality and time delays can all modify the interaction.

The ecological consequence is therefore best summarized as

$$\boxed{\text{consumer abundance and resource abundance can regulate one another}.}$$

Predation and herbivory connect individual feeding behavior to population dynamics and community structure.