What is a trophic cascade in ecology?

A trophic cascade is an ecological phenomenon triggered by adding or removing top predators, leading to reciprocal changes in predator and prey populations through a food chain. These changes often cause dramatic shifts in ecosystem structure and nutrient cycling. For example, removing wolves in eastern North America led to increased white-tailed deer and a decline in the plants they consume. Overfishing cod in the North Atlantic Ocean increased small open ocean fish, snow crab, and shrimp populations. This resulted in decreased large-bodied herbivorous zooplankton and increased phytoplankton. Trophic cascades can also improve water quality in lakes through biomanipulation .

How do living things in an ecosystem affect each other in a trophic cascade?

In a trophic cascade , the addition or removal of top predators triggers changes in the relative populations of predators and prey through a food chain, often resulting in dramatic changes in ecosystem structure and nutrient cycling. For example, removing wolves can lead to an increase in deer and a decline in the plants the deer eat. Similarly, overfishing of cod in the North Atlantic Ocean has led to an increase in small fish, snow crab, and shrimp. This, in turn, decreased large-bodied herbivorous zooplankton and increased phytoplankton. Trophic cascades also affect primary production and respiration rates, influencing the exchange of gases between ecosystems and the atmosphere.

What are the different levels (trophic levels) in a food chain or food web?

Trophic levels represent the different feeding positions in a food chain or food web within an ecosystem. The levels include: * Producers : The first and lowest level, consisting of autotrophs like green plants, algae, and phytoplankton, which produce their own food through photosynthesis. * Primary Consumers : The second level, which consists of herbivores that feed on producers. Omnivores can also be primary consumers if they exclusively eat plant material. * Secondary Consumers : The third level, consisting of carnivores and omnivores that prey on primary consumers. * Tertiary Consumers : Often large carnivores that prey on secondary consumers; also known as apex predators. * Decomposers : Organisms like bacteria and fungi that break down dead organisms and waste into nutrients that producers can use.

How can predators influence the population of plants or algae in an ecosystem?

Predators can trigger trophic cascades , causing significant changes to plant and algae populations in ecosystems. In a three-level food chain, an increase or decrease in carnivores affects the number of herbivores, which in turn impacts primary producers like plants and phytoplankton. For example, removing wolves can lead to more deer and fewer plants because the deer population is not controlled. Similarly, changes in predatory fish populations can control the biomass and production of phytoplankton, nutrient recycling, and other processes affecting the exchange of gases between lakes and the atmosphere. Overfishing of cod led to an increase in phytoplankton due to a decrease in herbivorous zooplankton.

What is an example of a trophic cascade happening in real life?

A trophic cascade is an ecological phenomenon where changes at the top of the food chain affect lower levels, often causing dramatic ecosystem changes. For example, the reintroduction of wolves to Yellowstone National Park led to a decrease in the elk population and an increase in vegetation like aspen and willow. Another example is the overfishing of cod in the North Atlantic Ocean, which led to an increase in small fish and phytoplankton. Similarly, the harvesting of sea otters off the western coast of North America resulted in an increase in sea urchins and a decline in kelp forests.

Why are trophic cascades important for balancing ecosystems and their biodiversity?

Trophic cascades are crucial for maintaining balanced ecosystems and biodiversity because they involve reciprocal changes in predator and prey populations through a food chain. These cascades, often triggered by removing or adding top predators, can cause dramatic changes in ecosystem structure and nutrient cycling. For example, removing top carnivores can lead to a mesopredator release, where medium-sized predators increase, causing a decline in the species they consume. Conversely, restoring top carnivores can help preserve the structure and processes of ecosystems, which provide essential services like food, clean water, and air. Research has demonstrated that trophic cascades control species composition, biomass, and the production of herbivores and plants.

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An energy pyramid diagram showing four levels: producers like grass at the base, primary consumers such as rabbits above, secondary consumers like snakes next, and a tertiary consumer, an eagle, at the top. Arrows indicate energy transfer upward and energy loss at each level.

Side-by-side illustration comparing an ecosystem before and after the removal of top carnivores. The left panel shows a balanced landscape with wolves, bears, foxes, diverse birds, and a variety of plants, while the right panel shows an ecosystem dominated by large herbivores like elk and deer, fewer predators, reduced plant variety, and less songbird diversity.

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yellow perch Yellow perch (*Perca flavescens*).

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Top Questions

What is a trophic cascade in ecology?
A trophic cascade is an ecological phenomenon triggered by adding or removing top predators, leading to reciprocal changes in predator and prey populations through a food chain. These changes often cause dramatic shifts in ecosystem structure and nutrient cycling.

For example, removing wolves in eastern North America led to increased white-tailed deer and a decline in the plants they consume. Overfishing cod in the North Atlantic Ocean increased small open ocean fish, snow crab, and shrimp populations. This resulted in decreased large-bodied herbivorous zooplankton and increased phytoplankton. Trophic cascades can also improve water quality in lakes through biomanipulation.
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2. trophic cascade
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How do living things in an ecosystem affect each other in a trophic cascade?
In a trophic cascade, the addition or removal of top predators triggers changes in the relative populations of predators and prey through a food chain, often resulting in dramatic changes in ecosystem structure and nutrient cycling.

For example, removing wolves can lead to an increase in deer and a decline in the plants the deer eat. Similarly, overfishing of cod in the North Atlantic Ocean has led to an increase in small fish, snow crab, and shrimp. This, in turn, decreased large-bodied herbivorous zooplankton and increased phytoplankton. Trophic cascades also affect primary production and respiration rates, influencing the exchange of gases between ecosystems and the atmosphere.
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1. trophic cascade
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What are the different levels (trophic levels) in a food chain or food web?
Trophic levels represent the different feeding positions in a food chain or food web within an ecosystem.

The levels include:
* Producers: The first and lowest level, consisting of autotrophs like green plants, algae, and phytoplankton, which produce their own food through photosynthesis.
* Primary Consumers: The second level, which consists of herbivores that feed on producers. Omnivores can also be primary consumers if they exclusively eat plant material.
* Secondary Consumers: The third level, consisting of carnivores and omnivores that prey on primary consumers.
* Tertiary Consumers: Often large carnivores that prey on secondary consumers; also known as apex predators.
* Decomposers: Organisms like bacteria and fungi that break down dead organisms and waste into nutrients that producers can use.
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How can predators influence the population of plants or algae in an ecosystem?
Predators can trigger trophic cascades, causing significant changes to plant and algae populations in ecosystems.

In a three-level food chain, an increase or decrease in carnivores affects the number of herbivores, which in turn impacts primary producers like plants and phytoplankton. For example, removing wolves can lead to more deer and fewer plants because the deer population is not controlled. Similarly, changes in predatory fish populations can control the biomass and production of phytoplankton, nutrient recycling, and other processes affecting the exchange of gases between lakes and the atmosphere. Overfishing of cod led to an increase in phytoplankton due to a decrease in herbivorous zooplankton.
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Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
What is an example of a trophic cascade happening in real life?
A trophic cascade is an ecological phenomenon where changes at the top of the food chain affect lower levels, often causing dramatic ecosystem changes.

For example, the reintroduction of wolves to Yellowstone National Park led to a decrease in the elk population and an increase in vegetation like aspen and willow. Another example is the overfishing of cod in the North Atlantic Ocean, which led to an increase in small fish and phytoplankton. Similarly, the harvesting of sea otters off the western coast of North America resulted in an increase in sea urchins and a decline in kelp forests.
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Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
Why are trophic cascades important for balancing ecosystems and their biodiversity?
Trophic cascades are crucial for maintaining balanced ecosystems and biodiversity because they involve reciprocal changes in predator and prey populations through a food chain. These cascades, often triggered by removing or adding top predators, can cause dramatic changes in ecosystem structure and nutrient cycling.

For example, removing top carnivores can lead to a mesopredator release, where medium-sized predators increase, causing a decline in the species they consume. Conversely, restoring top carnivores can help preserve the structure and processes of ecosystems, which provide essential services like food, clean water, and air. Research has demonstrated that trophic cascades control species composition, biomass, and the production of herbivores and plants.
1 Britannica Source
1. trophic cascade
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

trophic cascade, an ecological phenomenon triggered by the addition or removal of top predators and involving reciprocal changes in the relative populations of predator and prey through a food chain, which often results in dramatic changes in ecosystem structure and nutrient cycling.

In a three-level food chain, an increase (or decrease) in carnivores causes a decrease (or increase) in herbivores and an increase (or decrease) in primary producers such as plants and phytoplankton. For example, in eastern North America the removal of wolves (Canis lupus) has been associated with an increase in white-tailed deer (Odocoileus virginianus) and a decline in plants eaten by the deer. American zoologist Robert Paine coined the term trophic cascade in 1980 to describe reciprocal changes in food webs caused by experimental manipulations of top predators. In the 1980s others used the term to describe changes in aquatic ecosystems arising from factors such as sudden increases in predatory fish populations from stocking or dramatic declines in predatory fishes caused by overfishing.

Effects on aquatic and terrestrial ecosystems

trophic pyramidTrophic pyramid, also called an energy pyramid, showing the progression of food energy. The pyramid base contains producers, organisms that make their own food from inorganic substances. All other organisms in the pyramid are consumers. The consumers at each level feed on organisms from the level below and are themselves consumed by organisms at the level above. Most of the food energy that enters a trophic level is "lost" as heat when it is used by organisms to power the normal activities of life. Thus, the higher the trophic level on the pyramid, the lower the amount of available energy.

During the 1980s and ’90s a series of experiments demonstrated trophic cascades by adding or removing top carnivores, such as bass (Micropterus) and yellow perch (Perca flavescens), to or from freshwater lakes. Those experiments showed that trophic cascades controlled biomass and production of phytoplankton, recycling rates of nutrients, the ratio of nitrogen to phosphorus available to phytoplankton, activity of bacteria, and sedimentation rates. Because trophic cascades affected the rates of primary production and respiration by the lake as a whole, they affected rates of exchange of carbon dioxide and oxygen between the lake and the atmosphere.

sea otterA sea otter (*Enhydra lutris*) feeding on a sea urchin in the Kachemak Bay National Estuarine Research Reserve in Alaska.

Research in a wide variety of terrestrial and aquatic environments has shown that trophic cascades control species composition, biomass, and production of herbivores and plants. For example, overfishing of cod (Gadus morhua) and other commercially exploited fishes such as haddock (Melanogrammus) and hake (Urophycis, Raniceps, and Phycis) in the North Atlantic Ocean led to an increase in small pelagic (open ocean) fish consumed by cod, snow crab (Chionoecetes opilio), and shrimp. As a result, populations of large-bodied herbivorous zooplankton, which are consumed by small pelagic fishes, decreased, which in turn led to an increase in the phytoplankton. Restoration of wolves to the Bow Valley of Alberta, Canada, decreased the population of elk (Cervus elaphus) and increased the growth of aspen (Populus) and willow (Salix). In another example, the commercial harvesting of sea otters (Enhydra lutris) for the fur trade off the west coast of North America triggered an increase in sea urchins and a decline in kelp forests, because of kelp consumption by the urchins, in nearby marine environments.

Traditionally, plant production and nutrient cycling were thought to be controlled by physical or chemical factors, such as solar radiation, climate, and nutrient supply. While physical and chemical factors are important, producer communities and their metabolic rates are also influenced by trophic cascades.

Ecosystems without top predators

In many instances, trophic cascades have been initiated by human persecution and harvesting of top carnivores, such as wolves and big cats in terrestrial ecosystems and sharks, tunas, and game fish in aquatic ecosystems. The removal of top carnivores triggers significant effects on prey populations, primary producers, and ecosystem processes. Therefore, the conservation of top carnivores helps to preserve the structure and processes of ecosystems in which these predators live. The normal functioning of ecosystems provides many services used by people, including food, fibre, and freshwater supplies as well as processes that maintain the quality of air, water, and soil. The preservation or restoration of top carnivores, however, is sometimes controversial because of the risk such predators pose to people, livestock, or pets.

Mesopredator release, a phenomenon in which the populations of medium-sized predators rapidly increase and play greater roles in the ecosystems they inhabit, is caused by the removal of top carnivores. Mesopredators compete poorly with and may be consumed by top carnivores and thus tend to avoid them. The systematic decline of cougars (Puma concolor) and wolves in the conterminous United States and other parts of North America during the 20th century allowed populations of mesopredators such as coyotes (Canis latrans), red foxes (Vulpes vulpes), and raccoons (Procyon lotor) to increase, as food sources, hunting grounds, den sites, and other resources once controlled by top carnivores became available. The decline of leopards (Panthera pardus) in some parts of Africa allowed baboon (Papio) populations to increase. The loss of large sharks in the oceans allowed smaller-bodied sharks and rays to increase. In each case, mesopredator release caused a decline in species consumed by the mesopredator.

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In addition, some mesopredators have become nuisance species. Foraging raccoons plunder trash cans and gardens in many urban areas and are noted carriers of the rabies virus. Baboons can invade homes, break into cars to steal food, and in some cases pose a threat to children.

Biomanipulation in lakes

In lakes, trophic cascades are used to improve water quality through biomanipulation, a management practice in which humans intentionally remove whole species from ecosystems. The goal of biomanipulation is to reduce the concentration of harmful phytoplankton, such as toxic blue-green algae. The most direct method to control harmful phytoplankton blooms is to reduce inputs of nutrients such as phosphorus that drive their growth. In cases where the arrival of nutrients to the ecosystem is delayed or slow to develop, biomanipulation can be used to hasten the decline of harmful phytoplankton. The stocking of game fish (or their protection from harvest using special regulations) triggers a trophic cascade with decreases in the biomass of smaller-bodied fish, increases in the biomass of herbivorous zooplankton, and decreases in the biomass of harmful phytoplankton. In some cases plankton-eating fish have been removed directly by lake managers. In addition, the removal of bottom-feeding fish from shallow lakes leads to increases in rooted vegetation and increased water clarity as the rooted plants stabilize the sediments. This transition involves a trophic cascade, as herbivorous zooplankton increase in biomass and consume phytoplankton, but also involves the direct effects of rooted vegetation on sediment stability and nutrient cycling.

Stephen Carpenter

trophic cascade

Effects on aquatic and terrestrial ecosystems

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Ecosystems without top predators

Biomanipulation in lakes