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Levels of Organization
The biosphere is too large and complex for
most ecological studies. To study relationships
within the biosphere, ecologists look at differ-
ent levels of organization or smaller pieces of
the biosphere. The levels increase in complexity
as the numbers and interactions between
organisms increase. The levels of organization
are: organism, population, biological commu-
nity, ecosystem, biome, and biosphere. Refer to
Figure 7
as you read about each level.
Organisms, populations, and
biological communities
The lowest level of organization is the individ-
ual organism itself. In
Figure 7
on the next
page, the organism is represented by a single
fish. Individual organisms of a single species
that share the same geographic location at the
same time make up a
population.
The school of
fish represents a population of organisms.
Individual organisms often compete for the
same resources, and if resources are plentiful,
the population can grow. Usually there are
factors that prevent populations from becoming
extremely large. For example, when the popula-
tion has grown beyond what the available
resources can support, the population size
declines until it reaches the number of individ-
uals that the available resources can support.
The next level of organization is the
biological
community,
a group of interacting populations
that occupy the same geographic area at the
same time. Organisms might or might not
compete for the same resources in a biological
community. The collection of plant and animal
populations, including the school of fish,
represent a biological community.
Ecosystems, biomes, and the
biosphere
The next level of organization after a biological
community is an ecosystem. An
ecosystem
is a
biological community and all of the abiotic
factors that affect it. As you can see in
Figure 7
,
an ecosystem might contain an even larger
collection of organisms than a biological com-
munity. In addition, it contains the abiotic
factors present, such as water temperature and
light availability. Although
Figure 7
represents
an ecosystem as a large area, an ecosystem also
can be small, such as an aquarium or tiny
puddle. The boundaries of an ecosystem are
somewhat flexible and can change, and ecosys-
tems even might overlap. The next level of
organization is the biome.
A
biome
is a large group of ecosystems that
share the same climate and have similar types
of communities. The biome shown in
Figure 7
is a marine biome. All of the biomes on Earth
combine to form the highest level of organiza-
tion—the biosphere.
Get It?
Infer
what other types of biomes might be
found in the biosphere if the one shown in
Figure 7
is called a marine biome.
CROSSCUTTING CONCEPTS
Scale, Proportion, and Quantity
When building a model, it is important to
consider different measures of size, time, and energy. Design a model that
illustrates the levels of organization in the biosphere. Trade models with a
classmate and offer feedback about how changes in scale, proportion, or
quantity affect the performance of the model.
STUDY TIP
Question Session
Study the levels of organiza-
tion illustrated in
Figure 7
with a partner.
Question each other about the topic to deepen
your knowledge.
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Module 2 • Principles of Ecology