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SCIENCE
 

Loss of top link on food chain ripples down, upsets nature's balance

This raccoon is not afraid of predators — and that’s a bad thing, says scientist Justin Suraci. Because the largest predators are dying out and no longer a threat, smaller animals feel more secure and nature is thrown off-balance.
This raccoon is not afraid of predators — and that’s a bad thing, says scientist Justin Suraci. Because the largest predators are dying out and no longer a threat, smaller animals feel more secure and nature is thrown off-balance. Michael Clinchy

Picture a peaceful northern Pacific shoreline. As birds circle overhead, a raccoon slowly wanders across slippery rocks in search of a crab to eat.

Suddenly the sound of a hungry dog barking interrupts the calm of the scene. The raccoon grows worried and scampers off. Whatever crab the raccoon would have caught will live to see another day. The crab may catch a snail or two that otherwise would have gotten away. Fear has changed the balance of nature.

Justin Suraci is a scientist at the University of Victoria in Canada. He believes fear plays a bigger part in the natural world than is commonly realized. He also believes that the absence of fear can cause unexpected problems.

Fear of large predators keeps smaller predators in check, Suraci says. Fearful animals spend less time eating and more time worrying about getting eaten. In turn that allows their even smaller prey to thrive.

Larger Hunters Are Gone

All over the world animal fear is vanishing, however. Humans have killed off large predators in staggering numbers. Wolves, sharks, tigers, bears, lions and other large predators have almost completely disappeared from many parts of the world. With the fearsome hunters gone, the animals they hunt have grown much less fearful. Their absence of fear, Suraci says, is changing the natural world.

Large carnivores like wolves or tigers are known as apex or top predators. They are at the top of the food chain because no other animal hunts them. 

The importance of apex predators has long been understood. However, scientists have mostly focused on one thing: how their hunting keeps the populations of other kinds of animals from growing too large. 

Suraci thinks there is more to it than that. He believes fear of apex predators also plays an important part in preserving the balance of nature.

Fear Of Predators Plays A Role Too

A predator's influence goes far beyond the animals it eats, Suraci says. A predator also has the power to change the behavior of any creature that fears it. Fearful animals spend less time eating because they are too busy hiding or scurrying or keeping their heads up and their ears attuned to the approach of danger. Such behavior can have the same effect as if the animals really had been eaten.

To prove his theories Suraci set up an experiment on the Gulf Islands in British Columbia, Canada. The idea was to reintroduce fear to an area without any remaining apex predators.

Suraci decided to study the raccoons of the Gulf Islands. The bold animals had flourished basically unchecked since their natural predators — cougars, bears — were killed off by humans. They flocked to the shoreline's exposed rocks in search of tasty meals of fish and crab. As they looked for their prey they showed none of the cautious behavior one might expect of a medium-sized animal. 

Recreating Predators With Speakers

To make the raccoons fearful again, Suraci and his team set up speakers in the trees near the shore and broadcast the sounds of dogs barking. Then they filmed the raccoons' response.

The results were striking. The raccoons spent far less time in exposed areas than before. When they did appear in the open, they spent much more time scanning their surroundings. All told, the raccoons spent 66 percent less time looking for food than when they were unafraid of being eaten.

The effects of that shift quickly spread beyond the raccoons. The populations of two types of raccoon prey — crabs and fish — nearly doubled. Meanwhile, the number of periwinkle snails, which crabs prey on, fell significantly.

Restoring Fear, Restoring Balance

Bringing fear back "restored a balance to the food chain," Surac said. Such balance had been lost after humans eliminated the top level of predators from the area. When the balance of nature is upset, a variety of unexpected problems can occur, from species disappearing to dying trees, increasing wildfires and rapidly spreading diseases. 

Of course, recordings of barking dogs or roaring lions is not the answer. It would not take long for animals to figure out that the danger was not real. The only answer is to reintroduce the apex predators themselves. For that to happen, humans may have to lose their own fear of these mighty hunters.

We will have to get over fear of apex predators, Suraci says. Bringing them back is the only way to make the natural world healthy and rich.

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1
Anchor 3: People, Events & Ideas

What effect do apex predators have on smaller predators?

A

Apex predators make smaller predators more cautious.

B

Apex predators cause smaller predators to eat different foods.

C

Apex predators make smaller predators more curious.

D

Apex predators cause smaller predators to seek a new habitats.

2
Anchor 3: People, Events & Ideas

What happened when the raccoons became fearful again?

A

Apex predators returned to the area.

B

Raccoons spent more time looking for food.

C

The periwinkle snail population increased.

D

The amounts of crab and fish increased.

3
Anchor 4: Word Meaning & Choice

Read the excerpt below.

Fearful animals spend less time eating and more time worrying about getting eaten. In turn that allows their even smaller prey to thrive.

What is the BEST definition of "thrive" based on this excerpt?

A

become fearful

B

hide better

C

become strong

D

eat quickly

4
Anchor 4: Word Meaning & Choice

Read the excerpt below.

Suraci decided to study the raccoons of the Gulf Islands. The bold animals had flourished basically unchecked since their natural predators — cougars, bears — were killed off by humans.

What is shown by the word "unchecked" in the second sentence?

A

that people are not watching the raccoons

B

that the raccoons have no predators

C

that the raccoons are becoming less fearful

D

that smaller animals do not hide from raccoons

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