Chapter 18: Interactions of Living Things

■ Identify biotic and abiotic factors
in an ecosystem.
■ Describe the different levels of
biological organization.
■ Explain how ecology and the
environment are related.
Abiotic and biotic factors interact to
make up your ecosystem. The quality
of your ecosystem can affect
your health. Your actions can affect
the health of the ecosystem.
Review Vocabulary
climate: the average weather
conditions of an area over time
New Vocabulary
• ecology • community
• abiotic factor • ecosystem
• biotic factor • biosphere
• population
Figure 1 Ecologists study biotic and abiotic
factors in an environment and the relationships
among them. Many times, ecologists
must travel to specific environments to
examine the organisms that live there.
532 CHAPTER 18
WM. J. Jahoda/Photo Researchers
The Environment
Ecology
All organisms, from the smallest bacteria to a blue whale,
interact with their environment. Ecology is the study of the
interactions among organisms and their environment.
Ecologists, such as the one in Figure 1, are scientists who study
these relationships. Ecologists organize the environmental factors
that influence organisms into two groups—nonliving and
living or once-living. Abiotic (ay bi AH tihk) factors are the nonliving
parts of the environment. Living or once-living organisms
in the environment are called biotic (bi AH tihk) factors.
Why is a rotting log considered a biotic factor in
the environment?
Abiotic Factors
In any environment, birds, insects, and other living things,
including humans, depend on one another for food and shelter.
They also depend on the abiotic factors that surround them,
such as water, sunlight, temperature, air, and soil. All of these
factors and others are important in determining which organisms
are able to live in a particular environment.