Trophic Cascade Reference Cheat Sheet

Key Facts

• A trophic cascade occurs when a change in one trophic level causes population or behavior changes across two or more other trophic levels.
• In a simple three-level chain, predators decrease herbivores, and fewer herbivores often allow producers to increase.
• Top-down control means higher-level consumers strongly influence lower trophic levels, such as wolves reducing deer pressure on vegetation.
• Bottom-up control means nutrients, sunlight, water, or producer abundance limit the populations of higher trophic levels.
• Only about 10 percent of energy is typically transferred from one trophic level to the next, so energy available at level n is about 0.1 times the energy at the level below.
• A keystone species has a large ecological effect compared with its abundance, and removing it can trigger a trophic cascade.
• Direct effects occur when one species immediately affects another, while indirect effects occur when the effect passes through one or more intermediate species.
• Food webs make cascades more complex because omnivores, alternative prey, and multiple predators can weaken or redirect the cascade.

Vocabulary

Trophic Cascade

A chain reaction in an ecosystem where a change at one trophic level affects organisms at other trophic levels.

Trophic Level

A feeding position in an ecosystem, such as producer, primary consumer, secondary consumer, or tertiary consumer.

Keystone Species

A species that has a major effect on ecosystem structure even if it is not very abundant.

Top-Down Control

Regulation of an ecosystem by predators or higher-level consumers that influence the abundance or behavior of lower levels.

Bottom-Up Control

Regulation of an ecosystem by resources such as nutrients, sunlight, water, or producer biomass.

Biomass Pyramid

A diagram showing the total mass of living material at each trophic level, usually decreasing at higher levels.