CHAPTER 4
ECOSYSTEMS AND COMMUNITIES
4-1 The Role of Climate
What is Climate?
• Weather – the day-to-day condition of Earth’s
atmosphere at a particular time and place.
• Climate – the average, year-after-year
conditions of temperature and precipitation in
a particular region.
• Climate is caused by many factors, including
the trapping of heat by the atmosphere, the
latitude, the transport of heat by winds and
ocean currents, and the amount of
precipitation that results. The shape and
elevation of landmasses also contribute to
global climate patterns.
• The energy of incoming sunlight drives Earth’s
weather and helps determine climate.
The Greenhouse Effect
• Carbon dioxide, methane, water vapor, and a
few other atmospheric gases trap heat energy
and maintain earth’s temperature range.
• Greenhouse effect – the natural situation in
which heat is retained by this layer of
greenhouse
gases
• The gases trap heat inside Earth’s atmosphere.
If these gases were not present in the
atmosphere, Earth would be 30 degrees
Celsius cooler than it is today.
The Effect of Latitude on Climate
• Since Earth is a sphere that is tilted on its axis,
solar radiation hits different parts of Earth’s
surface at an angle that varies throughout the
year. At the equator, the sun is almost directly
overhead at noon all year. At the North and
South poles, the sun is much lower in the sky
for months at a time.
• As a result of differences in latitude and the
angle of heating, Earth has three main climate
zones: polar, temperate, and tropical.
• Polar zones – cold areas where the sun’s rays
strike Earth at a very low angle (North and
South
Poles)
• Temperate zones – lie between the polar
zones and the tropics, temperature changes
from hot to
cold depending on the season.
• Tropical zone – near the equator, receives
direct or almost direct sunlight year-round.
Climate is always warm.
Heat Transport in the Biosphere
• The unequal heating of Earth’s surface drives
winds and ocean currents, which transport
heat throughout the biosphere. Winds form
because warm air rises and cool air sinks. Air
that is heated near the equator rises. Cooler
air over the poles sinks toward the ground.
The upward movement of warm air and the
downward movement of cool air create air
currents, or winds, that move heat through
the atmosphere.
4-2 What Shapes an Ecosystem?
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Biotic and Abiotic Factors
Ecosystems are influenced by a combination of
biological and physical factors.
Biotic factors – the biological influences on
organisms within an ecosystem
Ex. – birds, trees, mushrooms, and bacteria
Abiotic factors – physical (non-living) factors that
shape ecosystems
Ex. – temperature, precipitation, wind, sunlight
Together, biotic and abiotic factors determine the
survival and growth of an organism and the
productivity of the ecosystem in which the
organism lives.
• Habitat – the area where an organism lives
• Niche – the full range of physical and
biological conditions in which an organism
lives and the way in which the organism uses
those conditions
• Niche includes the type of food the organism
eats, how it gets this food, and which other
species use the organism as food.
• Ex. – a mature bullfrog catches insects,
worms, spiders, small fish, or even mice.
Predators such as herons, raccoons, and
snakes prey on bullfrogs. They live in or near
the water of ponds, lakes, and slow-moving
streams. Their body temperature changes
with that of the surrounding water and air.
Their niche also includes when and how it
reproduces.
• No two species can share the same niche in
the same habitat, but different species can
occupy niches that are very similar.
Community Interactions
• Community interactions, such as competition,
predation, and various forms of symbiosis, can
powerfully affect an ecosystem.
• Competition – occurs when organisms of the
same or different species attempt to use an
ecological resource in the same place at the
same time. (resource is any necessity of life)
• Direct competition in nature often results in a
winner and a loser, with the losing organism
failing to survive.
• Competitive exclusion principle – states that
no two species can occupy the same niche in
the same habitat at the same time.
• Predation – an interaction in which one
organism captures and feeds on another
organism.
• The organism that does the killing and eating
is called the predator and the organism that
gets eaten is the prey.
• Symbiosis – any relationship in which two
species live closely together
• Three main symbiotic relationships:
mutualism, commensalism, and parasitism
• Mutualism – both species benefit from the
relationship. (ex – flowers provide some insects
with food and the insect helps the flower
reproduce)
• Commensalism – one member benefits and the
other is not affected.(barnacles attach to a whale
because they eat food that is being carried by the
water flowing past the swimming whale, these
barnacles do not affect the whale at all)
• Parasitism – one organism lives on or inside
another organism and harms it. (tapeworms,
fleas, ticks, lice)
Ecological Succession
• Ecosystems are constantly changing in
response to natural and human disturbances.
As an ecosystem changes, older inhabitants
gradually die out and new organisms move in,
causing further changes in the community.
• Ecological succession – the series of
predicable changes that occurs in a
community over time
• Can result from slow changes in the
environment or a sudden disturbance from
human activity like clearing a forest.
• Primary succession – on land, succession that
occurs on surfaces where no soil exists (new
islands from volcanic eruptions)
• Pioneer species – the first species to populate
the area (often lichens, which is made up of a
fungus and an alga that grows on bare rock)
• Secondary succession – the return of an
ecosystem to its original condition after a
disturbance (such as fires or human activities)
4-3 Biomes
• Biome – a group of ecosystems that have the
same climate and dominant communities
• Different species adapt to their biomes. If
moved to a different biome, they may not
survive.
• Tolerance – ability to survive and reproduce
under conditions that differ from their optimal
conditions.
• For example, plants and animals of the
Arizona desert can tolerate temperatures that
range from very hot to below freezing.
However, some rain forest plants and animals
die quickly if the temperature drops below
freezing or rises above 34° C for long.
• Too much or too little of any environmental
factor can make it difficult for an organism to
survive.
Biomes and Climate
• Microclimate – the climate in a small area that
differs from the climate around it
• Ex – certain streets in San Francisco are often
covered in fog while the sun shines brightly
just a few blocks away
The Major Biomes
There are ten different biomes:
• Tropical rain forest
tropical dry forest
tropical savanna
desert
temperate grassland
temperate woodland and shrubland
temperate forest
northwestern coniferous forest
boreal forest
tundra
Each of these biomes is defined by a unique set
of abiotic factors, particularly climate, and a
characteristic assemblage of plants and animals
Tropical rain forest – hot and wet year-round,
nutrient-poor soils
plants - evergreen trees, ferns, woody
vines and climbing plants
wildlife – sloths, jaguars, anteaters,
toucans, parrots, butterflies, ants, beetles
where? Parts of South and Central
America, Southeast Asia, parts of Africa,
Southern India, Northeastern Australia
Tropical dry forest – rainfall is seasonal, not
year-round. Trees shed leaves in the dryseason to save water (deciduous), warm
year-round, rich soils subject to erosion
plants – tall, deciduous trees
wildlife – tigers, monkeys, elephants,
pelicans, termites, snakes, lizards
where? Parts of Africa, South and Central
America, Mexico, India, Australia, tropical
islands
Tropical Savanna – Has a cover of grasses, isolated
trees, warm temperatures, seasonal rainfall,
compact soil, frequent fires from
lightning
plants – tall grass, trees or shrubs
wildlife – lions, leopards, cheetahs, hyenas,
aardvarks, elephants, giraffes, antelopes,
zebras, baboons, eagles, ostriches,
storks, termites
where? Large parts of eastern Africa,
southern Brazil, and northern Australia
Desert – low precipitation, variable
temperatures, soil rich in minerals but
poor in organic material
plants – cacti, plants with a short growth
cycle
wildlife – mountain lions, gray foxes,
bobcats, deer, antelopes, bats, owls,
hawks,
roadrunners, ants, beetles, butterflies,
flies, wasps, tortoises, rattlesnakes, lizards
where? Africa, Asia, Middle East, US,
Mexico, South America, Australia
Temperate grassland – warm to hot summers,
cold winters, seasonal precipitation, fertile
soils, occasional fires
plants – grass and herbs resistant to
drought, fire, and cold
wildlife – coyotes, badgers, mule, deer,
antelopes, rabbits, hawks, owls, chickens,
snakes, ants, grasshoppers
where? Central Asia, North America,
Australia, Central Europe, South America
Temperate woodland and shrubland – hot, dry
summers and cool, moist winters, thin
nutrient-poor soil, some fires
plants – evergreen shrubs with small leaves,
herbs that grow during winter and die in
summer
wildlife – coyotes, foxes, bobcats, mountain
lions, deer, rabbits, squirrels, hawks, quails,
lizards, snakes, butterflies
where? Western coasts of North and South
America, areas around Mediteranean Sea
South Africa, Australia
Temperate forest – cold to moderate winters,
warm summers, year-round precipitation,
fertile soils
plants – deciduous trees, some conifers
(produce seed-bearing cones and have
leaves
shaped like needles), flowering shrubs,
ground layer of mosses and ferns
wildlife – deer, black bears, bobcats,
squirrels, raccoons, skunks, songbirds,
turkeys
where? Eastern US, southeastern Canada,
most of Europe, parts of Japan, China, and
Australia
Northwestern coniferous forest – mild
temperatures, a lot of precipitation during
the fall, winter,
and spring, cool dry summer, rocky soils
plants – fir, spruce, hemlock, redwood
trees
wildlife – bears, elk, deer, beavers, owls,
bobcats, weasels
where? Pacific coast of northwestern US
and Canada from northern California to
Alaska
Boreal forest – long cold winters, short mild
summers, moderate precipitation, high
humidity,
nutrient-poor soils
plants – needleleaf coniferous trees
(spruce, fir) some broadleaf deciduous
trees, small berry-bearing shrubs
wildlife – lynxes, timber wolves, weasels,
moose, beavers, songbirds
where? North America, Asia, northern
Europe
Tundra – strong winds, low precipitation, short
soggy summers, long cold dark winters
plants – mosses, lichens, sedges, short
grasses
wildlife – birds and mammals that can
handle harsh conditions, shore birds, ox,
Arctic foxes, caribou, small rodents
where? Northern North America, Asia, and
Europe
Other Land Areas
• Some areas of land on Earth don’t fall into the
major biome categories. This include
mountain ranges and polar ice caps.
Mountain ranges can be found on all continents.
The abiotic and biotic conditions vary with
elevations. As you go up, the temperature gets
colder and precipitation increases.
Polar ice caps are the icy polar regions that
border the tundra. They are cold year-round.
There are not a lot of plants and animals. Polar
bears, seals, insects, and mites are the dominant
animals in the north polar region. Penguins and
marine mammals are the dominant animals in
the south polar region.
4-4 Aquatic Ecosystems
• Almost ¾ of the Earth’s surface is covered with
water
• Aquatic ecosystems are determined primarily
by the depth, flow, temperature, and
chemistry of the overlying water
Freshwater Ecosystems
• Only 3% of the surface water on Earth is fresh
water.
• Freshwater ecosystems can be divided into
two main types: flowing-water ecosystems
and standing-water ecosystems
• Flowing-Water Ecosystems – Rivers, streams,
creeks, and brooks are all freshwater
ecosystems that flow over the land.
Organisms that live there are well adapted to
the rate of flow.
• Standing-Water Ecosystems – lakes and ponds
are the most common standing-water
ecosystems. There is usually water circulating
within them. This circulation helps to
distribute heat, oxygen, and nutrients
throughout the ecosystem.
The still waters of lakes and ponds provide
habitats for many organisms, such as plankton,
that would be quickly washed away in flowing
water.
• Plankton – tiny, free-floating organisms that
live in freshwater and saltwater environments.
• Phytoplankton – unicellular algae that are
supported by nutrients in the water and form
the base of many aquatic food webs
• Zooplankton – planktonic animals that eat the
phytoplankton
Freshwater Wetlands –
• Wetland – an ecosystem in which water either
covers the soil or is at or near the surface of
the soil for at least part of the year. May be
flowing or standing and fresh, salty, or
brackish (mixture of fresh and salt water)
The three main types of freshwater wetlands are
bogs, marshes, and swamps.
• Estuaries - wetlands formed where rivers meet
the sea. Contain a mixture of fresh water and
salt water
• Types of estuaries include salt marshes and
mangrove swamps.
• Salt marshes are temperate-zone estuaries
dominated by salt-tolerant grasses above the
low-tide line and by seagrasses underwater.
• Mangrove swamps are coastal wetlands that
are widespread across tropical regions
Marine Ecosystems
• Photic zone – well-lit upper layer of the
ocean. This is where photosynthesis occurs.
• Aphotic zone – permanently dark layer of the
oceans below the photic zone.
• Marine biologists also divide the ocean into
zones based on the depth and distance from
shore: the intertidal zone, the coastal ocean,
and the open ocean.