WGBH CPB
How Disruptions Affect Animal Populations

Disturbing Nature's Balance

As the video from Page 1 showed, habitat loss affects the creatures that live there. This includes not only the wild animals but humans, too.

Factors that upset the balance of an ecosystem, such as habitat loss, are called disruptions. Disruptions can lead to population shifts. Population shifts are lasting changes in the numbers or kinds of animals that usually live in the ecosystem. The most severe effect of a disruption is the extinction of one or more species. 

Certain disruptions are caused by specific natural events, such as forest fires, severe storms, and volcanic eruptions. Others are caused by more widespread changes, such as temperature or rainfall patterns. As you'll learn in this lesson, disruptions may also result from human activities. These include clearing land for farming or building, killing pests, and bringing species to a place they don't normally live.

Food web diagram.
Diagram showing a terrestrial food web, with a tree and grass as primary producers, an owl, hawk, and fox as top predators, and several other animal species represented. Arrows show the feeding relationships between predators and prey.

In a food web model, arrows indicate feeding relationships. Food (energy) moves in the direction of the arrow. Most members of an ecosystem are connected to more than one organism.

Measuring Ecosystem Health

  • Scientists measure an ecosystem's health by studying the species in it and the connections they share.
  • Animals in an ecosystem depend on one another and the physical environment.
  • The loss of any one species—whether it’s a predator or the prey it feeds on—can affect many others in the ecosystem. So can changes to the physical environment.

Before moving on, review key vocabulary used in the lesson using Match It.

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Example: A/an ECOSYSTEM contains all the living things in a given area plus the nonliving parts like sunlight, soil, and water.

An animal that hunts and eats other animals for food is a/an PREDATOR.

EXTINCTION refers to the permanent loss of a species.

A/an ENDANGERED SPECIES is a type of living thing that exists in such small numbers that it is in danger of disappearing from the planet.

PREY describes animals that are hunted and eaten by other animals for food.

A/an FOOD WEB is a complex model that shows how various food chains in an ecosystem are connected.

A change in biological or physical conditions that upsets the balance of an ecosystem is called a/an DISRUPTION.

A large and lasting change in the usual numbers or kinds of animals that live in an ecosystem is called a/an POPULATION SHIFT.

HABITAT LOSS describes the process that forces living things from their natural home or environment.

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