Science High School Reviewer | Grade 4 Science | Life Science | Exploring Ecosystems | Lesson 8: Introduction to Ecosystems

An ecosystem is made of living and nonliving parts that all work
together. Every organism in an ecosystem has a part to play.

An ecosystem is all the
living and nonliving things in an environment and the many
ways they interact. An ecosystem may be large, like a desert, or
small, like a rotting cactus.
Animals, plants, fungi, protists, and bacteria are the living
parts of an ecosystem. These organisms interact with each other
and with the nonliving parts of the system. The nonliving parts
of an ecosystem include air, water, soil, sunlight, climate, and
landforms.

Biotic Factors
Scientists call the living things in an
environment biotic (bye•AH•tik) factors. Plants,
animals, and bacteria are all biotic factors. You
are a biotic factor, too!
Abiotic Factors
Your desk, pen, pencil, and textbook are
abiotic (ay•bye•AH•tik) factors. Abiotic factors are
all the nonliving things in an environment. Other
abiotic factors are water, rocks, soil, and light.
Climate (KLYE•mit) is another. Climate refers to
the typical weather pattern in an environment.

The biotic and abiotic factors
of an environment make up an
ecosystem.

Kinds of Ecosystems
Organisms can survive only in environments
in which their needs are met. In any
environment, some kinds of plants and
animals will survive better than others.
Some will not survive at all. The kinds
of plants and animals that live in
an area depend on the soil and the
climate. Plants and animals that
do well in a desert ecosystem
have adaptations that help
them conserve water and stay
cool. For example, the stems
of a giant saguaro cactus can
expand to fill up with water.
This is one way that the plant
has adapted to the hot, dry
environment. It can store
plenty of water until the
next rainfall.

Desert
The driest ecosystem is a
desert. Some plants and
animals have adapted to
the limited water supply.
Cactuses, shrubs, coyotes,
and roadrunners are desert
organisms.

Grassland
Grasslands, as their name
suggests, are covered with
tall grasses. They receive
a medium amount of rain.
Grasshoppers, prairie
chickens, and bison are
animals that live in the
grasslands of North America.

Tundra
A tundra is a cold, dry region.
The ground beneath the
surface is frozen all year long.
Some grasses can grow in a
tundra, but trees cannot. In
the spring and summer, arctic
foxes, caribou, and other
animals thrive in these areas.

Forest
Forests are filled with trees,
wildflowers, and animals.
Forests usually get more rain
than grasslands. Deer, foxes,
raccoons, and squirrels often
live in forests.

Tropical Rain Forest
Rain forests are always wet.
They get rain year-round. A
rain forest supports thousands
of species of plants and
animals. Colorful birds such
as the toucan and beautiful
flowers such as the orchid live
in rain forests.

Organisms and Their Environment
A population is all the members of one species
that live within an area of an ecosystem. In a desert
ecosystem, there are many different populations. All the
prairie dogs make up one population. Among the plants,
barrel cactuses make up a population. The size of each
population may change depending on the amount of
food, water, and space that is available.
The different populations that interact with each other
in the same area form a community. All the organisms
in a desert ecosystem form a community.
The area or place where an organism lives in an
ecosystem is called a habitat. You can think of a habitat
as an organism’s “address.” In the Sonoran Desert, the
habitat of the Gambel’s quail is near shrubs where it can
hide from predators. The habitat of a saguaro cactus seed
is a shrub that provides a shady environment. A habitat
contains all the living and nonliving things that an
organism needs.

A population is all
the members of a species that live
in an ecosystem. For example, the
bullfrogs in a pond make up one
population. Water lilies are another.

All of the populations in an
ecosystem make up a community.
A pond community may have
populations of bullfrogs, fish, water
lilies, and dragonflies. The size of a
community depends on factors such as
food, shelter, and light. Communities
in warm, moist ecosystems tend to
outnumber those in cold or dry places.

Special Roles
If an organism’s habitat is its address, its niche is its
job. Each organism in an ecosystem has a different job,
or role. The specific role an organism has in its habitat
is called its niche. A niche includes the type of food
the organism eats, how it gets its food, and which other
species use the organism as food. Adaptations also help
determine an organism’s niche.
Each population in a habitat has a different niche.
For example, a hummingbird and a roadrunner share
the same desert habitat. However, they do not have the
same niche. A Lucifer hummingbird eats spiders, small
insects, and nectar from various plants. It will perch on
the branches of tall plants to avoid one of its enemies,
the roadrunner. The roadrunner’s niche as a predator
includes chasing scorpions, lizards, and snakes for food.
Its niche as prey that other organisms hunt for food
includes running to escape enemies, such as the coyote.