This document discusses factors that shape ecosystems and communities. It explains that climate is determined by factors like greenhouse gases, latitude, and ocean currents. Ecosystems are shaped by biotic interactions between organisms as well as abiotic factors like temperature and soil. Communities change over time through ecological succession as environments change and new species move in. The document outlines 10 major terrestrial biomes and describes 3 main types of aquatic ecosystems - freshwater, estuaries, and marine - which are classified based on factors like depth, flow, and salinity.

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Name____________________________ Class__________________ Date __________
Chapter 4 Ecosystems and Communities
In the atmosphere, temperature, precipitation, and other environ-
mental factors combine to produce weather and climate. Weather
is the day-to-day condition of Earth’s atmosphere at a certain time
and place. Climate is the average yearly condition of temperature
and precipitation in a region. Climate affects ecosystems. Several
factors decide climate.
• Carbon dioxide and other atmospheric gases trap heat
energy and maintain Earth’s temperature range. These
gases function like the glass windows of a greenhouse.
Therefore, the trapping of heat by gases in the atmosphere
is called the greenhouse effect. This greenhouse effect helps
temperatures on Earth stay within a range that supports life.
• Latitude also affects climate. Earth has three main climate
zones: polar, temperate, and tropical.
▪ Polar zones are cold areas where the sun’s rays strike
Earth at a very long angle.
▪ Temperate zones sit between the polar zones and the
tropics. The climate in these zones ranges from hot to cold,
depending on the season.
▪ The tropical zone, or tropics, is near the equator. The
climate here is almost always warm.
• Unequal heating of Earth’s surface also causes winds and
ocean currents. Winds and currents move heat through the
biosphere.
4–2 What Shapes an Ecosystem?
Organisms in ecosystems are affected by both biotic and abiotic
factors. Biotic factors are all of the living things with which organ-
isms interact. Abiotic factors are nonliving, physical things. They
include temperature and soil type. Together, biotic and abiotic
factors determine the survival and growth of an organism and
the productivity of the ecosystem in which an organism lives.
A habitat is the area where an organism lives. A habitat has
both biotic and abiotic factors. A niche includes all of the abiotic
and biotic things in an organism’s habitat and the way the organ-
ism uses those things. For example, a niche includes what an
organism eats and how it gets its food.
Summary
4–1 The Role of Climate

2. Name____________________________ Class__________________ Date __________
Community interactions, such as competition, predation, and
symbiosis, can powerfully affect an ecosystem.
• Competition occurs when living things try to use the
same resources. Competition often results in one organism
dying out.
• Predation occurs when one organism (the predator) captures
and eats another (the prey).
• Symbiosis occurs when two species live close together in
one of three ways.
1. Mutualism: Both species benefit from the relationship.
2. Commensalism: One species benefits. The other is neither
helped nor harmed.
3. Parasitism: One species benefits by living in or on the
other. The other species is harmed.
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 is the
series of predictable changes that occur in a community over time.
• Primary succession takes place on bare rock surfaces where
no soil exists. Pioneer species are the first species to live in
these areas.
• Secondary succession occurs when a disturbance changes a
community without removing the soil.
4–3 Biomes
A biome is a group of land communities that covers a large area
and has a certain soil type and climate. Within a biome, there may
be microclimates. A microclimate is a small area where the climate
differs from that of the surrounding area. A species may live over
a large or small area, depending on its ability to survive and
reproduce under tough conditions.
There are ten major biomes: tropical rain forest, tropical dry
forest, tropical savanna, desert, temperate grassland, temperate
woodland and shrubland, temperate forest, northwestern conif-
erous forest, boreal forest (or taiga), and tundra.
Each biome has its own set of abiotic factors and a typical
collection of organisms. Some areas, such as mountains and polar
ice caps, do not fall neatly into the major biomes.
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4–4 Aquatic Ecosystems
Unlike land biomes, which are grouped geographically, aquatic
ecosystems are grouped by the abiotic factors that affect them.
Aquatic ecosystems are described mainly by the depth, flow,
temperature, and chemistry of their water.
In many aquatic ecosystems, tiny free-floating swimming
organisms can be found. These organisms are called plankton.
Two types of plankton are phytoplankton and zooplankton.
Phytoplankton are single-celled algae that use nutrients in water
to make food. They form the base of many aquatic food webs.
Zooplankton are animals that feed on phytoplankton.
There are three main groups of aquatic ecosystems.
1. Freshwater ecosystems can be divided into several types.
• Flowing-water ecosystems (rivers and streams) flow
over land.
• Standing-water ecosystems include lakes and ponds.
• Freshwater wetlands include bogs, marshes, and swamps.
In wetlands, water covers the soil or is present at or near
the surface for at least part of the year.
2. Estuaries are wetlands formed where rivers meet the sea.
They contain a mixture of fresh and salt water. Most food
made in estuaries enters food webs as tiny pieces of organic
matter, called detritus.
• Salt marshes are temperate estuaries. Salt-tolerant grasses
and seagrasses are the dominant plant life in salt marshes.
• Mangrove swamps are tropical estuaries. The dominant
plant life in mangrove swamps includes several species of
salt-tolerant trees, called mangroves, and seagrasses.
3. Marine ecosystems exist in the ocean. The ocean is divided
into zones based on how much light penetrates the water.
• The photic zone is the well-lit upper layer of water.
Photosynthesis can take place here.
• The aphotic zone is the permanently dark lower layer of
water. Producers here use chemosynthesis to make food.
The ocean is also divided into three zones based on depth
and distance from shore: the intertidal zone, the coastal ocean,
and the open ocean.
• Organisms in the intertidal zone are exposed to regular
and extreme changes in their surroundings.
• The coastal zone is relatively shallow, lies entirely within
the photic zone, and is often rich in plankton and other
organisms. Coral reefs grow in tropical coastal oceans.
• The open ocean is the largest zone, covering more than
90 percent of the surface area of the world’s oceans. These
areas typically have low levels of nutrients and support
only small producers.
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