The Ecology Book

64

chemically damaging the reef. If the

parrotfish was overfished or died

out from disease, the health of the

reefs would rapidly deteriorate.

Landscape managers

On African grasslands, elephants

smash down small and medium-

sized trees for food, helping

maintain savanna as grassland

and opening up new areas that

were formerly woodland. This

destructive behavior helps

maintain the feeding habitat for

grazing animals such as zebras,

antelope, and wildebeest. It also

indirectly helps the predators that

hunt the grazers—including lions,

cheetahs, and hyenas—and the

smaller mammals that burrow in

grassland soils. Without the

elephants, these animals would

soon disappear. Elephants are also

very important seed dispersers;

KEYSTONE SPECIES

undigested seeds pass through

their gut, are then defecated, and

later germinate. Up to one-third

of all West African tree species

depend on elephants for their seed

dispersal. Elephants also dig and

maintain waterholes, which benefit

many other species.

Forest-dwelling Asian elephants

have a similar role. In southeast

Asia, they smash through gaps and

clearings in woodland, opening up

holes in the canopy. The new plants

that grow in these unshaded areas

add to the forest’s plant and animal

diversity and also help a broader

range of animals to thrive there.

Keystone predators

The sea otter is a marine mammal

that lives in the Pacific coastal

waters of North America. In the

18th and 19th centuries, they were

hunted extensively for their fur. By

the early 20th century, they had

been wiped out in many areas, and

their total population was thought

to be fewer than 2,000 individuals.

Since 1911, legal protection has led

to a slow increase in numbers.

Sea otters are important

because they eat large numbers

of sea urchins. These seafloor-

dwelling invertebrates graze on the

lower stems of kelp that grow up

Every species in the coastal

zone is influenced in one way

or another by the ecological

effects of sea otters.

James Estes

American marine biologist

Each pack of wolves in the

Yellowstone National Park has its own

territory. Many of the territories overlap,

and numbers fluctuate from year to

year, with 108 wolves recorded in 2016.

Yellowstone wolfpack territories

Snake River

Lamar

Canyon

Cougar

Canyon

8 Mile

Cinnabar

Bechler

Mollie’s

Prospect

Peak

Wapiti

Lake

Junction

Butte

SCALE

10km (6 miles)

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