---
title: "Keystone Species — AP Enviro Definition & Exam Guide"
description: "A keystone species has a huge impact on its ecosystem relative to its abundance. Learn how AP Enviro tests it in succession, trophic cascades, and wetlands."
canonical: "https://fiveable.me/ap-enviro/key-terms/keystone-species"
type: "key-term"
subject: "AP Environmental Science"
---

# Keystone Species — AP Enviro Definition & Exam Guide

## Definition

Keystone species are organisms that have a disproportionately large impact on their ecosystem relative to their abundance. They play a crucial role in maintaining the structure and function of an ecosystem.

## Related Study Guides

- [2.7 Ecological Succession](/ap-enviro/unit-2/ecological-succession/study-guide/9nK9VTaGMUhfWvoRySDr)
- [8.4 Human Impacts on Wetlands and Mangroves](/ap-enviro/unit-8/human-impacts-on-wetlands-mangroves/study-guide/kxkfXkF2OACm1Tcwb8u7)

## Review

### Related Terms

- Trophic cascade: A trophic cascade occurs when changes in the population size of one species at one trophic level result in indirect effects on other trophic levels.
- Ecological niche: An ecological niche refers to the specific role and position that a species has within its environment, including its interactions with other organisms and its use of resources.
- Indicator species: Indicator species are organisms whose presence, absence, or abundance can provide information about certain environmental conditions or changes.