Summary
Top predator effects ripple down through lower trophic levels, as in wolves reintroduced to Yellowstone.
In depth
Top-down control: removing predators increases herbivores and decreases plants. Wolf reintroduction in Yellowstone in 1995 reduced elk browsing, and willow and aspen regrew, though the extent of effects is debated. Bottom-up control is limited by nutrients.
Strength differs among systems; strong in lakes and marine systems, weaker in complex terrestrial webs. Mesopredator release occurs when top predators are lost.
Example: loss of sharks may increase rays and reduce scallops.
The idea comes from Hairston, Smith and Slobodkin (1960) and Paine. In lakes, adding piscivorous fish reduces planktivores, raises zooplankton and clears the water of algae (Carpenter and Kitchell). In the northern Pacific, orca predation on sea otters, triggered by decline in other prey, led to urchin growth and kelp loss. On land, cascades are weaker than in water, in many cases.
Cascades can be top-down, as above, or bottom-up, when nutrients change plant quality. Reintroducing predators is a tool for rewilding, though results vary. Fear effects, which change prey behaviour, may matter as much as the killing itself.
Example: when the wolf was returned to Yellowstone in 1995, elk numbers and behaviour changed, with willow growth along rivers increasing.
Frequently asked questions
What is Trophic Cascade?
Top predator effects ripple down through lower trophic levels, as in wolves reintroduced to Yellowstone.
Which area of biology covers Trophic Cascade, and how advanced is it?
Trophic Cascade is one of the 54 topics in Ecology. It is rated Advanced, so it suits learners who want specialist depth. Related topics in this area include Eutrophication, Keystone Species, Food Web.
Can you give an example of Trophic Cascade?
Sea otters limit urchins that would overgraze kelp.
What should I learn before Trophic Cascade?
Work through the Beginner topics in Ecology first, such as Ecology, Ecosystem, Biotic and Abiotic Factors, then return to Trophic Cascade. Advanced topics assume the Intermediate vocabulary.
What topics are related to Trophic Cascade?
The closest topics to Trophic Cascade are Eutrophication, Keystone Species, Food Web, Ecological Stoichiometry. Comparing them side by side is a good way to see how the ideas connect.
How can I check that I understand Trophic Cascade?
Read the summary and the in-depth section, then use the quick check on the interactive lesson for Trophic Cascade. To practise the whole of Ecology, use the Ecology quiz.
How is Trophic Cascade different from Eutrophication?
Trophic Cascade: Top predator effects ripple down through lower trophic levels, as in wolves reintroduced to Yellowstone. Eutrophication: Nutrient enrichment of water bodies causing algal blooms, oxygen depletion and fish kills. Read both side by side and note what each one explains.
How should I study Trophic Cascade step by step?
First, read the summary and write the definition in your own words. Second, read the in-depth section and note any example. Third, compare it with Eutrophication and explain the difference aloud. Finally, take the Ecology quiz and come back to this page for any question you miss.