Biology Now, 2e

Here and Gone ■ 385

The temperate forest biome is dominated by trees and shrubs

adapted to relatively rich soil, snowy winters, and moist, warm

summers. These forests display greater species diversity than do the

tundra and boreal forest biomes: oak, maple, hickory, beech, and elm

are common. Herbivores include squirrels, rabbits, deer, raccoons, and

beavers, while bobcats, mountain lions, and bears make up the

carnivores. Amphibians and reptiles are common.

The grassland biome cannot sustain vigorous tree growth, but its moisture

levels are not as low as in deserts. Grasslands are found in both temperate

and tropical latitudes and are dominated by grasses and herbaceous plants

such as coneflower and shooting star. Scattered trees are found in some,

such as the tropical grasslands known as the savanna. Burrowing rodents

like voles and prairie dogs may aerate the soil, thereby improving growing

conditions. Many grasslands have been converted to agriculture.

Because air in the desert

biome lacks moisture, it does

not retain heat well. As a

result, temperatures can be

above 113°F (45°C) in the

daytime and then plunge to

near freezing at night. Desert

plants have small leaves to

minimize water loss.

Succulents, such as cacti,

store water in their fleshy

stems or leaves. Most animals

in the desert are nocturnal,

hiding in burrows during the

heat of the day and emerging

at night to feed.

Estuaries are the shallowest but most productive of
the aquatic biomes. They are tidal ecosystems where
rivers flow into the ocean. They have a constant ebb
and flow of fresh and salt water, and organisms must
be able to tolerate daily changes in saltwater
concentrations. The plentiful light, the abundant
supply of nutrients delivered by the river system, and
the regular stirring of nutrient-rich sediments by
water flow create a rich and diverse community of
photosynthesizers. Grasses and sedges are the
dominant vegetation in most estuaries.

The marine biome,

characterized by salt water,

is the largest biome on our

planet. The coastal region

stretches from the shoreline

to the edge of the

continental shelf and is

highly productive because

of the availability of

nutrients and oxygen. A

majority of Earth’s marine

species live in the coastal

region. The intertidal zone,

closest to the shore, is a

challenging environment

where organisms such as

seaweeds, worms, crabs,

sea stars, sea anemones,

and mussels are submerged

and exposed to dry air on a

twice-daily basis. The

relatively nutrient-poor open

ocean begins about 40

miles offshore and is much

less productive than coastal

waters.

Equator

30° N

30° S

Figure 21.8

Amazing biomes

Biomes do not begin and end abruptly,

but rather transition into one another.

Terrestrial biomes are categorized by

temperature, precipitation, and altitude;

aquatic biomes are determined by

proximity to shorelines.