In AP Environmental Science, a predator-prey relationship is a species interaction in which one organism (the predator) hunts and consumes another organism (the prey) for food, helping move energy up through trophic levels and regulate population sizes.
A predator-prey relationship is one of the basic ways two species interact in an ecosystem. The predator eats the prey, and the prey becomes the predator's food (and energy) source. The College Board states this plainly in EK ERT-1.A.1: the predator is an organism that eats another organism, the prey.
This isn't just "who eats whom." It's a feedback loop. When prey are plentiful, predators have lots to eat and their numbers climb. More predators then eat more prey, so prey numbers drop. With less food, predator numbers fall, which lets prey recover. Picture two waves that rise and fall just slightly out of sync. That back-and-forth is what AP Enviro means by predator-prey population dynamics, and it ties directly to how resource availability shapes species interactions (LO 1.1.A).
This term lives in Unit 1: The Living World: Ecosystems, across topics 1.1 (Introduction to Ecosystems) and 1.9 (Trophic Levels). It supports learning objective AP Enviro 1.1.A, which asks you to explain how resource availability influences species interactions, and it connects to AP Enviro 1.9.A on how energy flows through trophic levels. Every time a predator eats prey, energy moves from a lower trophic level to a higher one (EK ENG-1.B.3), so predation is literally how energy climbs the food chain. Understanding this sets you up for the bigger Unit 1 themes of energy flow, matter cycling, and what keeps populations stable.
Keep studying AP Environmental Science Unit 1
Trophic Levels and Energy Flow (Unit 1)
Predation is the mechanism that moves energy upward. When a predator eats prey, energy passes from one trophic level to the next, which is exactly the upward flow described in EK ENG-1.B.3.
Keystone Species (Unit 1)
A keystone predator holds an ecosystem together. Remove it and prey populations explode, which can trigger a trophic cascade that reshapes the whole community.
Symbiosis and Competition (Unit 1)
Predation sits alongside symbiosis (mutualism, commensalism, parasitism) and competition as the main species interactions in topic 1.1. They all answer the same question: how do organisms affect each other when resources are limited?
Resource Partitioning (Unit 1)
Both ideas trace back to limited resources. Competition pushes species to partition resources, while predation directly controls how much of a resource (the prey) is even available.
Expect this term in MCQs that test population dynamics, energy flow, and species interactions. You might see a stem asking what role the predator plays, how a predator-prey relationship affects population sizes over time, or which scenario best shows a trophic cascade caused by predation. You may also get questions on predator-prey adaptations, like camouflage or speed, and which species the adaptation benefits. No released FRQ has used this term verbatim, but the concept supports free-response prompts on food webs, energy transfer between trophic levels, and how losing a top predator destabilizes an ecosystem. Be ready to describe the oscillating boom-and-bust pattern of predator and prey populations.
Both involve one organism feeding off another, so they get mixed up. The difference is outcome and timing. A predator kills and eats its prey quickly, then moves on. A parasite lives on or in its host over a long period and usually keeps the host alive while feeding off it. Parasitism is a form of symbiosis (EK ERT-1.A.2); predation is not.
In a predator-prey relationship, the predator eats the prey, and this is how energy moves up from one trophic level to the next.
Predator and prey populations rise and fall in a linked, slightly out-of-sync cycle: more prey leads to more predators, which then drives prey numbers back down.
Predation is one of the core species interactions in topic 1.1, alongside symbiosis and competition, and all three are shaped by resource availability.
A keystone predator can control an entire community, so removing it can set off a trophic cascade.
Predator-prey adaptations like speed, camouflage, and warning coloration evolve because they help one species survive the interaction.
It's a species interaction where one organism, the predator, hunts and eats another organism, the prey, for food. The College Board defines it in EK ERT-1.A.1, and it appears in Unit 1 topics 1.1 and 1.9.
No. Symbiosis is a close, long-term interaction between species, like mutualism, commensalism, or parasitism. A predator quickly kills and eats its prey, so it isn't considered symbiosis on the AP exam.
A predator kills its prey and eats it fast, then moves on to the next meal. A parasite lives on or in a host over a long time and usually keeps the host alive while feeding. Parasitism is a type of symbiosis; predation is not.
The two populations cycle together. When prey are abundant, predator numbers grow; the growing predator population then eats down the prey, which causes predator numbers to fall and lets prey recover. You'll see this oscillating pattern tested in MCQs.
A trophic cascade happens when removing or adding a top predator ripples through the food web and changes populations at lower trophic levels. Keystone predators are the classic example, and trophic cascades show up directly in AP practice questions about predator-prey relationships.
Connect this key term to the AP exam workflow: review the course, practice questions, and check related study tools.
Review units, study guides, and course resources.
Check this vocabulary in multiple-choice context.
Apply key concepts in written AP responses.
Estimate the exam score you are working toward.
Review the highest-yield facts before practice.
Put the full course together before test day.