Chapter 6 - Biomes

I. Biome

A. definition: a major type of ecosystem covering

a large region that is characterized by a

distinctive climate and types of organisms

1. each biome is made up of many individual

ecosystems

2. there are two main types of biomes

a. terrestrial (land)

i. determined by average

temperature and amount of

precipitation

b. aquatic (water)

i. determined by water depth,

nutrient content, and nearness to

land

B. Vegetation

1. Because the plants that grow in an area

determine the other organisms that can live

there (base of the food web), biomes are

often described by their vegetation.

2. Plants will have characteristics, specialized

structures, or other adaptations that allow

them to survive in that particular biome.

a. Examples: size, shape, color,

reproductive methods

3. Climate often determines what types of

plants can grow in an area.

4. climate: the average weather conditions in

an area over a long period of time

a. includes many factors such as

temperature, precipitation, humidity,

winds

b. most important are temperature and

precipitation

5. In general, the higher the temperature and

the greater the amount of precipitation, the

taller and denser the vegetation is.

a. See figure 3, page 144

C. Latitude and Altitude

1. latitude: the distance north or south of the

equator

2. altitude: the height above sea level

3. Climate varies with latitude and altitude.

a. Increases in latitude and altitude result

in colder climates.

4. Temperate region: land between 30° and

60° north latitude and 30° and 60° south

latitude

a. Most of the food is grown in this region

due to the moderate temperatures and

fertile soil

D. Forest biomes are the most widespread and

diverse of the biomes.

1. large trees require lots of water

2. temperatures range from mild to hot,

precipitation is plentiful

3. Three main types of forests – tropical

(rain), temperate (deciduous), and

coniferous (taiga)

II. Tropical Rain Forests

A. located around the Earth near the equator

1. help to regulate the world’s climate and play a

large role in the elemental cycles of nitrogen,

carbon, and oxygen

2. always humid, warm

a. precipitation of 200 cm – 450 cm per

year

b. receive direct rays from the sun during

most of the year

c. temps. average 25° C all year

d. growing season can last 12 months

e. possible to have wet and dry seasons or

for rain to fall all year

B. Nutrients

1. The nutrients in the rain forest exist primarily

in the organisms.

2. Decay happens incredibly fast – conditions are

ideal with moisture and warm temperatures.

a. Dead organic matter does not last for long, as

it is quickly absorbed by the plants, and so the

soil does not get very enriched by the process.

b. Fallen trees and other organic matter is

decomposed and recycled in a matter of days

and weeks instead of months or years.

3. Surprisingly, the soil is very poor and low in

nutrients as a result.

a. The nutrients that are available in the soil are

in the top 5 – 10 cm of soil.

b. Because of this arrangement of soil, rain

forest tree trunks must widen at their bases

and form above ground roots called

buttresses. This allows the roots to be shallow

in the ground and use the soil efficiently.

4. Layers of the Rainforest – different types of plants

grow in different layers

a. There are 4 main layers above the forest floor

– emergent, upper canopy, lower canopy, and

understory.

b. Emergent trees: consists of the tallest trees,

which reach heights of 60 – 70m

i. Trunks of these trees can reach 5m in

circumference

ii. Grow and emerge into direct sunlight

iii. Eagles, bats, monkeys live in this layer

c. Canopy – under the emergent layer,

considered the primary layer of the forest

i. Can be divided into upper and lower

portions

ii. Trees can reach over 30m tall

iii. The canopy absorbs up to 95% of the

sunlight, with the lower canopy receiving

less than the upper canopy

iv. Most animals in the rain forest live in the

canopy, some never touching the ground.

d. Understory – underneath the canopy

i. Receives very little sunlight

ii. Trees and shrubs must be adapted to lots

of shade

iii. Heights max at about 3.5m

5. Species Diversity

a. Has the greatest amount of species diversity of

any biome – the more we look for species, the

more we find and the possibilities are

mindboggling – 43 species of ants on 1 tree!

b. Animal diversity is caused by 2 factors:

i. Diversity of the plants (provides lots of

niches)

ii. Wide variety of habitats supplied by the

different layers of the forest (conditions

are very different from high in the

canopy to low in the understory)

c. Most rainforest animals are specialized

species using narrow niches that avoid

competition

d. Rainforests cover between 5-7% of the

Earth’s surface yet contain at least 50% of all

plant and animal species of the world.

6. Threats to the Rainforest

a. Every minute of every day, 100 acres of

tropical rain forests are cleared for logging

operations, agriculture, or oil exploration.

b. In 1950, over 10% of the Earth’s surface was

rainforest – now it’s far less.

c. Deforestation: destruction of a forest as the

result of human activity

i. Most of the rainforests are located in

developing countries that are faced with

rapid population growth.

ii. Driving the destruction is the human

demand for space and wood.

d. Along with the vast numbers of plant and

animal species that are threatened are the

native people and their cultures.

e. The trade of exotic plants and animals is also

a major threat.

f. While small areas of rain forests that are

burned may possibly regenerate after

hundreds of years, large tracts or bulldozed

areas where the soil has been disrupted will

not be able to regenerate – only weeds will

grow instead of the lush rain forest.

I. Temperate Deciduous Forests

A. deciduous trees: trees that shed their leaves at a

particular season of the year

1. form many niches used by other organisms

2. located in the temperate zone, generally

between 30º and 50º latitude

3. most deciduous forests are located in the

Northern hemisphere although there are some

in the Southern hemisphere

B. Climate

1. Temperature

a. varies greatly from 30-35ºC in the summer

to -3ºC (-22ºF) in the winter

b. variety of seasons

2. Precipiation

a. Falls as rain or snow

b. Approximately 50 cm to 300 cm of

precipitation a year

c. Falls regularly (no rainy or dry seasons)

d. Growing season is 4 – 6 months

C. Structure

1. The forest has several layers, each with its own

group of plant species

a. Canopy

i. Made of upper branches and leaves of

tall trees

ii. Catches most of the sunlight but some

does filter down to the lower layers

b. understory

i. made of trees younger and smaller

than the canopy

ii. located directly beneath the canopy

c. shrubs

i. beneath the understory

d. mosses, ferns, and other plants grow on

the forest floor since sunlight penetrates to

that level

2. Soil

a. Leaves from the trees decay quickly

during the summer months

b. Produces a deep rich layer of humus

(organic content)

c. Humus and fallen leaves are home to many

insects and other invertebrates

d. Leaves act as insulation during the winter

months

D. Organisms

PLANTS:

1. deciduous trees are adapted to the variable

climate

a. During shorter daylight hours and cooler

temperatures, the trees lose their leaves

and become dormant, allowing them to

conserve water during the winter months.

b. During winter, they survive on food stored

in their roots, branches, and trunks.

c. Examples of deciduous trees:

Hickory, maple, ash, oak, birch, beech, etc.

2. In the spring, when sunlight increases and

temperatures rise, trees grow new leaves, seeds

germinate, and rhizomes (underground stems

used in asexual reproduction) and roots grow

new shoots and stems

ANIMALS:

1. Because the deciduous forest produces

abundant food and has many different

habitats, it supports a diverse community of

animals and other organisms.

2. Fungi and other decomposers, along with

insects and invertebrates, are common in the

leaf litter.

a. These organisms are preyed upon by

birds, mice, and small mammals

b. Reptiles and amphibians are common in

warmer forests

c. Filling the higher trophic levels are

predators such as wolves, mountain lions,

foxes, and coyotes

d. Eagles, owls, hawks, and other predatory

birds are also present

3. Most of the birds in the temperate deciduous

forest are migratory.

a. Each fall these birds fly south for the

warmer weather and the availability of

food.

b. Each spring, they return north to nest and

feed.

c. There are some birds that do not migrate,

such as the cardinal.

4. Animals that do not migrate must adapt to

survive the winter; many enter some type of

dormancy.

E. Human Impacts on the Temperate Deciduous

Forest

1. very little of the original deciduous forest is left

In Pennsylvania -

a. Heart’s Content

b. Parts of the Allegheny National Forest

2. Two factors have driven the human

consumption of the deciduous forest

a. Rich soil

i. The soil is deep and fertile, so it’s

excellent for farming.

b. trees themselves

i. deciduous trees have harder wood

than the conifers, making it a better

building material

ii. wood is also used for making paper

products and as fuel

3. The forest ecosystem regenerates slowly

because many species that were dependent on

the trees have disappeared from the area.

4. Replanted forests tend to have very low tree

and plant diversity, so many niches are no

longer present.

II. Taiga – Northern Coniferous Forest

A. Location

1. generally limited to the Northern hemisphere

just below the Arctic Circle

a. northern parts of former Soviet Union

b. northern parts of North America (Canada,

Alaska)

2. far, far from the Equator

B. Climate

1. temperature

a. average temperatures in the winter fall

below freezing and often reach -20ºC

b. summers are warm and last 2-4 months,

but depending on the latitude, the growing

season can be as short as 50 days

2. precipitation

a. 40-200 cm falls each year as rain in the

summer and snow in the winter

b. winter snow acts as an insulating blanket

i. traps heat

ii. prevents ground from freezing solid

iii. protects the roots of trees and small

animals that would normally freeze to

death

C. Diversity

1. The taiga / coniferous forest is not very diverse.

a. Most contain only a few species of trees:

pine, hemlock, fir, spruce, cedar

b. Some do have a few broad-leafed trees

such as aspen and larch.

c. Trees grow in dense stands; this prevents

most of the sunlight from reaching the

forest floor – the forest floor is usually

dark with little vegetation.

2. The soil is acidic: the trees’ needles are acidic

and decompose very slowly.

a. Poor soil and lack of sunlight prevent most

plants from growing on the forest floor.

b. Soil forms slowly due to the climate and

the acidity of the leaves actually slows

decomposition.

D. Organisms

PLANTS

1. Coniferous means “cone bearing” and

coniferous trees produce seed cones.

a. Leaves are needles which are long, thin

and covered in a thick waxy substance

which helps the tree to conserve water

when moisture in the ground is frozen and

unavailable.

b. The shape of the trees helps the tree to

shed snow which can become very heavy

and cause damage.

2. Most conifers are evergreen, which means they

don’t lose all of their leaves at a given time each

year.

ANIMALS

1. Animals have to adapt to cold winters and

coniferous trees.

a. Many animals are seed eaters such as

mice, squirrels, jays, and other rodents

b. Large herbivores feed on plants and the

bark, including moose, elk, beaver,

snowshoe hare. Many feed on whatever

vegetation happens to be available.

c. Predators pursue the herbivores – grizzly

bear, wolves, lynx

2. Almost all animals have thick body coverings

to protect them from the cold.

a. The difference in the summer and winter

coats can be significant in color and

thickness – snowshoe hare changes from

brown in the summer to white in the

winter.

3. Many animals migrate, hibernate, or live

under the snow. Some animals, such as shrews

and rodents, burrow underground to survive

the winter months.

4. The taiga has many lakes and swamps that in

summer attract birds that feed on insects, fish,

and other aquatic organisms.

5. Many of these birds fly south to avoid the very

harsh winter.

Desert Biomes:

FYI: Deserts occupy approximately 25% of the land surface

of the Earth, yet contain about 1% of the Earth’s biomass.

I. Characteristics

A. Soil

1. rich in minerals, poor in organic material

2. Leaching: process of rainwater moving

through the soil and carrying minerals

deeper into the soil

3. Since there is little rainfall, there is very

little leaching in the desert. As a result,

the upper layers of soil are rich in

minerals.

4. Little rainfall also means:

a. Few plants are able to live there

b. Extremely slow decay of organic

material

5. Pavement: desert floor; made mostly of

hard baked sand and bare rock particles

a. the pavement becomes exposed as

the loose soil is removed by wind

B. Climate

1. usually less than 10 cm. of rain per year,

rarely more than 25 cm.

2. lack of precipitation is the limiting factor

a. Precipitation determines the plants

in the desert, which are the base of

the food chain and so determine the

animals

3. Rain usually runs-off rather than being

absorbed by the soil because the

pavement is so dry and compacted

4. Temperature: varies greatly because there

is little moisture in the air, making it very

hot during the day and very cold at night

C. Organisms

1. All are adapted to survive 2 things:

a. Lack of water

b. Extreme temperatures

2. Adaptations can be physical or behavioral

PLANTS:

1. Need to absorb scarce water from the

ground and prevent water loss

2. Succulents: plants that have thick fleshy

water-filled stems and leaves

Example: cactus

3. Many succulents have a waxy coating to

limit transpiration

4. Spines: leaves of some plants; prevent or

reduce water loss through their size and

shape; also prevent grazing

5. Roots: there are 2 common strategies

a. Shallow roots spread over a large area

for maximizing the amount of absorbed

rainfall when it does rain

b. Single, very deep “tap root” to use

aquifers and other ground water as a

source of water

6. When conditions are too dry, some plants

will die and drop seeds that stay dormant

until the next rainfall. Germination

happens quickly and is often followed by

blooms – reproduce before the soil is dry

again.

ANIMALS:

1. Outer coating to prevent/reduce water loss

a. Exoskeletons of insects

b. Thick scales of reptiles

2. Many animals, such as desert rodents, use

underground burrows to survive the heat

3. Nocturnal: describes animals that are active

at night and sleep during the day; in the

desert, this allows the searing heat of the

day to be avoided

4. Estivation: type of dormancy; in this case

used by amphibians in the desert to survive

the summer; bury themselves in the ground

and remain dormant during the dry season

5. Nesting in cactuses to avoid predators and

extreme temperatures is a common practice

by some animals.

D. Desert Formation

General Process

1. Radiation over the Equator causes lots of

evaporation, so there’s lots of moist air over the

Equator. This water returns to Earth in

rainstorms.

2. After the rain falls, the air is very dry and flows

toward the Poles, becoming cooler and heavier in

the process.

3. Outside of the tropics, the dry denser air sinks

down to the Earth’s surface and pulls the water

out of the land. These dry winds result in

deserts.

Exact Location of Deserts

1. Determined in part by local geographical

features

2. Warm air that is forced over mountains loses its

moisture on one side and cools as it goes over the

rest of the mountains. When the cool, dry air

reaches the other side of the mountains, it can

pick up moisture from the soil, leaving it dry. A

desert begins to form.

3. The process described above is called the

rainshadow effect.

E. Desertification

1. Deserts are often bordered by areas that are dry

but not as dry as a desert.

2. These areas are called semi-arid regions.

3. These regions support grasses and shrubs.

4. desertification: process of changing the semi-arid

land into desert as a result of human activity

5. can happen through:

a. too many animals grazing, eroding the

topsoil by removing plants faster than they

can recover

b. Without the topsoil, bare land reflects more

heat and changes weather

c. without rain or topsoil, the area becomes a

desert

The Tundra I. Tundra

A. Location:

Northern Hemisphere: just south of the polar ice

caps and primarily north of the Arctic Circle in

Alaska, Canada, Greenland, Iceland, Norway, and

Asia

Southern Hemisphere: where it would be located is

covered by oceans

1. one of the largest biomes – almost 10% of the

Earth’s surface

2. lack of biodiversity makes the tundra fragile and

unstable (there are fewer organisms in the

tundra than in any other biome)

B. Climate

1. precipitation: less than 25 cm per year

2. air temperature: rarely above 10 C; most

precipitation is ice or snow

3. Temperature is the limiting factor of the tundra.

4. Active Zone: top layer of soil that thaws in the

summer, approximately 8 cm thick

5. Permafrost: located beneath the active zone, this

soil never thaws (until recently!)

6. Rain from the summer months can’t drain

through the permafrost, so it collects at the surface

to create bogs, marshes, ponds, small streams

a. these wet areas are crucial because they are

breeding grounds for insects, which are very

important in the food chains

C. Organisms

PLANTS:

common plants are mosses, shrubs, and grasses;

lichens are also common, covering vast areas of rock

1. Plants are small and grow close to the ground to

get radiant energy from the sun (from the sunlit

soil) and to avoid the punishing fierce winds.

2. Roots are limited to being close to the surface and

cover a wide area because they can’t penetrate the

permafrost and the soil is thin.

3. summer growing season = 60 days

ANIMALS:

common year-round residents include musk oxen,

Arctic fox, Arctic hare, polar bears, wolverines

1. Many others are seasonal visitors, migrating to or

through the tundra including birds, Arctic wolves,

caribou, moose, deer

2. Smaller animals, such as mice, lemmings, and

rabbits, burrow underground during the winter

yet remain active.

3. Few species live in the tundra, so many birds

migrate to the tundra during the breeding season

because there are fewer predators and food is

plentiful in the form of some plants, mollusks,

worms, and especially insects.

4. Food chains of the tundra are very simple and

therefore easily disrupted.

Common Food Chain of the Tundra

grasses insects birds Arctic fox

5. Adaptations of Animals in the tundra

a. thick coat which holds in air (acts as an

insulator to prevent heat loss)

b. wide hooves or feet because they make it easier

to move through the snow or mud

c. compact body to prevent heat loss – compare

and contrast the Arctic hare and the desert

jackrabbit

body compactness

thickness of fur

size/length of ears and limbs

D. Threats to the Tundra

1. Because of the extreme conditions of the tundra,

the land is easily damaged and slow to recover.

2. In recent years, oil has been located in the tundra

in areas such as Prudhoe Bay in northern Alaska.

3. This has led to many problems – oil exploration,

extraction, and transport has been a source of

disruption to the plants and animals of the region.

4. Pollution caused by spills and/or leaks of the oil

and other toxic materials associated with its

extraction may poison the water and food of this

fragile biome.

Grasslands

I. Grassland: an ecosystem in which there is too much water to

form a desert but not enough water to support a forest

A. Location

1. begin on the edges of the desert biome and stretch

to the forest biome

2. exist in Africa, central Asia, South America,

Australia, North America, parts of Europe

B. Climate

1. The desert-grassland boundary is the area between

deserts and grasslands where increased rainfall

enables some grasses and occasionally clumps of

trees to grow.

2. These areas are generally a little wetter than

deserts.

3. Each type of grassland has its own range of

precipitation and temperature; varies for each.

C. Organisms

1. grasses are the most common organisms

a. most of the biomass of grasses is underground

b. not as affected and able to rebound from fire

and lack of rain

2. limiting factor is rainfall

3. grass fires are vital to the grasslands:

a. prevents forests from overgrowing the area by

destroying trees and saplings

b. eliminates dead grass which accumulates

during the year, allowing water and air to

reach the soil for a new growth of grasses

c. releases valuable nutrients and minerals

d. the germination of many seeds is aided by fire

or even requires fire

4. grazing animals keep trees and shrubs from taking

over the grasslands

5. burrowing animals (prairie dogs, earthworms,

insects) aerate the soil

D. Particular Characteristics

1. determined by both abiotic and biotic factors

2. timing of the rain

a. some grasslands have rainy and dry seasons

b. these help to determine the specific type of

organisms in each region

II. Savanna

A. Definition: a plain full of grasses and scattered trees

and shrubs; found in tropical and subtropical

habitats and mainly in regions with a dry climate

1. found in western India, Africa, South America,

northern Australia

2. contain a large variety of grazing animals and the

predators that hunt them

B. Climate

1. precipitation varies in extremes

2. dry season and wet/rainy season

3. rain levels can reach as high as 150 cm per year,

but the majority falls in the rainy season

4. temperature is relatively stable year round

C. Organisms

PLANTS:

1. grasses, shrubs, and scattered trees are the most

common

2. often plants grow runners: large horizontal root

systems by which they obtain water during the dry

season

a. runners can be used in reproduction

b. protected from fires and grazing

c. allow plants to recover quickly and grow after

a fire

3. grasses grow in tufts – large clumps of tall coarse

grasses

4. many plants have vertical leaves to reduce exposed

surface area and limit water loss

5. some trees will lose their leaves during the dry

season to conserve water

6. thorns or sharp leaves are common on plants to

protect from grazing animals

7. plants are able to grow very quickly

a. recover from fire

b. better use of water during the rainy season

ANIMALS

1. migratory way of life for grazing herbivores,

following the rains to find food and water

2. predators follow these animals and stalk them

for food

3. must take advantage of the rainy season - many

reproduce during the rainy season when food is

abundant and young have the best chance of

survival

4. Animals are often concentrated in small areas

around streams and watering holes.

5. Because of this concentration, many animals

feed in a vertical feeding pattern : different

animals eat vegetation at different heights

a. Example: small gazelles eat grasses, rhinos

eat shrubs, giraffes eat tree leaves

b. Enables animals with different eating habits

to feed in the same areas without competing

for food

c. Animals occupy small, specific niches

III. Temperate Grasslands

A. Location

1. located on the interiors of continents where too

little rain falls for trees to grow

2. include the prairies of North America, the steppes

of Russia and Ukraine, the pampas of South

America

3. Mountains often play a crucial role in maintaining

grasslands – influences the amount of rainfall

particular areas receive

4. example: Rocky Mountains block rainfall from the

west across North America, so areas immediately

east of the mountains receives little rainfall. The

further eastward you go, the rain increases and the

grasslands change accordingly.

B. Climate

1. most have hot summers and cold winters

2. rainfall is moderate compared to a forest,

averaging 50-88 cm of precipitation a year

3. have the most fertile soil of any biome and so the

consumption of the temperate grassland has been

driven by agriculture

C. The Steppe

1. steppe: grasslands of short bunchgrasses that get

less than 50 cm of rain per year

a. bunchgrasses: short fine-bladed grass that

grows in clumps

b. clumping helps to conserve water by holding it

in a small root area which is under the shade

of the grass

2. most of the rain on the steppe evaporates quickly

because of high winds and high temperatures

3. plant life is sparse

4. some scientists consider areas of steppe to be

deserts rather than grasslands

5. large areas of steppe are located within the wetter

areas of deserts and the drier areas of prairies

D. The Prairie

1. prairie: characterized by rolling hills, plains, and

sod-forming grasses

a. sod-forming grasses: grasses that form a matte

of soil and roots; roots hold soil together (like

your lawn)

b. has a significant layer of humus which is

formed by the dead roots of grasses

c. the humus holds water, provides nutrients and

food for plants to grow

2. prairie makes up most of the grasslands of the

United States (also called the Great Plains)

3. large, fertile areas where the human population

gets the majority of its food (the reason for the

prairie to be called the “bread basket” of the US)

4. Rain on the prairie averages about 50-75 cm per

year

ANIMALS for the Steppe and Prairie

1. adapt to the changing conditions of the grasslands

by hibernating, migrating, or burrowing

underground

2. grasses are only slightly damaged by natural

grazing because the animals move from place to

place allowing the land to recover

E. Agriculture and Its Effects

1. Farming and ranching practices have caused

extensive damage to the grasses

a. Concentrated grazing in small areas destroys

the grass

b. Replacement of native grasses with grasses

that aren’t adapted to the environment have

also damaged the land

c. New grasses die more easily

d. New grasses take longer to reproduce, so fewer

animals can be supported

2. Can lead to situations such as the Dust Bowl of the

1930’s which was caused by:

a. Overgrazing

b. Poor farming practices

c. Series of droughts

3. Some nations are replacing generalized grassland

species with specialized agricultural species

a. Native grazing animals have been replaced

with huge herds of cattle and sheep

b. Native grasses replaced with grains such as

wheat and corn

c. Other native organisms are hard to find

because of the human demand for space and

food (e.g. armadillo, deer, wolves, bears, bison)

IV. Chaparral

A. Chaparral: a type of temperate woodland biome with

vegetation that is dominated by broad-leafed

evergreen shrubs

B. Location and Climate:

1. located in areas with warm, dry summers and mild,

wet winters

2. primarily in coastal areas that have Mediterranean

climates

3. middle latitudes, about 30° north and south of the

equator

C. Organisms

PLANTS:

1. most chaparral plants are low-lying, evergreen

shrubs and small trees that tend to grow in dense

patches

a. include chamise, manzanita, scrub oak, olive

trees, and herbs (sage, bay, rosemary)

b. have small, leathery leaves that retain water

2. The leaves also contain oils that promote burning.

a. Natural fires destroy trees that are

competition for sunlight and space

b. The oils give these plants their characteristic

taste and smell.

3. The chaparral plants are so well adapted to fire

that they can sprout from small bits of surviving

plant tissue.

ANIMALS:

1. Common animals include quail, lizards,

chipmunks, mule deer

2. Camouflage is a common adaptation

D. Threats to the Chaparral

1. greatest threat worldwide is human development

the chaparral’s moderate year-round climate and

location near oceans make it desirable for

commercial and residential use