Managing Our Natural Resources, 6e, Camp - 30

U n i t i Introduction

Source: USDA, Agricultural Research Service, photo by Stephen Ausmus

30

FIguRE 3-4 removing the

debris from the spillway of
this water impoundment
will drastically affect the
ecosystem.
In its most basic sense, an ecosystem is an energy system. Every part of an ecosystem interacts with the other parts of the system and depends on them. Fish in
a lake use oxygen from the atmosphere that is dissolved in the water. The plants in
the lake use light from the sun and minerals from the lake water and the land below
the lake to grow. All the processes in an ecosystem depend on energy. In fact, we
can say accurately that nothing happens in an ecosystem without the flow of energy.
To have a complete ecosystem, there must be three kinds of organisms present. There must be producers, usually green plants that produce new food (sugar)
by means of photosynthesis. There must be consumers that can take that primary
source of food, incorporate other chemicals and energy forms, and change it
into more complex organic compounds, foods, and tissue. Finally, there must be
decomposers that break the organic materials back down into their constituents
for reuse in the ecosystem. One organism can be a member of more than one of
the components. For instance, a green plant can be both producer and consumer.
A fungus can be both consumer and decomposer, as are animals. We will see how
these relate to each other in the section on food webs later in this chapter.
An ecosystem can be defined in many different ways. In one sense, a terrarium in
your classroom is an ecosystem. In another sense, your classroom makes up an ecosystem, and the terrarium is simply a part of that ecosystem. In yet another sense, your
school campus is part of an ecosystem that could be defined in geographic terms.
That brings us to what could be called the "Ultimate Concept in Ecology."
Everything on earth is part of one or more ecosystems. In each system, if you do
something to one part, it affects some or all the other parts of the system. The
effects are often unpredictable and may be very extreme.

Ecological Succession
At any given time in a particular ecosystem, there is probably a wide variety of
living things. No ecosystem is ever completely and permanently stable. For that
reason, there is no real "balance of nature." All ecosystems are dynamic, that is,
constantly changing. One species of plant or animal is replaced by another as
conditions change and as the ecosystem matures. The replacement of one species
by another in a maturing ecosystem is ecological succession (Figure 3-5).
Perhaps an example would make this clear. Consider a pond that has been
constructed by a landowner living in a region characterized by forests. Initially,
algae will be the only plant in that pond. Later, water lilies and cattails will
appear. After many years, the pond will fill up with sediment and become dry



Table of Contents for the Digital Edition of Managing Our Natural Resources, 6e, Camp

Contents
Managing Our Natural Resources, 6e, Camp - Cover1
Managing Our Natural Resources, 6e, Camp - Cover2
Managing Our Natural Resources, 6e, Camp - i
Managing Our Natural Resources, 6e, Camp - ii
Managing Our Natural Resources, 6e, Camp - iii
Managing Our Natural Resources, 6e, Camp - iv
Managing Our Natural Resources, 6e, Camp - v
Managing Our Natural Resources, 6e, Camp - Contents
Managing Our Natural Resources, 6e, Camp - vii
Managing Our Natural Resources, 6e, Camp - viii
Managing Our Natural Resources, 6e, Camp - ix
Managing Our Natural Resources, 6e, Camp - x
Managing Our Natural Resources, 6e, Camp - xi
Managing Our Natural Resources, 6e, Camp - xii
Managing Our Natural Resources, 6e, Camp - xiii
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Managing Our Natural Resources, 6e, Camp - xviii
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Managing Our Natural Resources, 6e, Camp - xxi
Managing Our Natural Resources, 6e, Camp - xxii
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Managing Our Natural Resources, 6e, Camp - Cover4
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