Managing Our Natural Resources, 6e, Camp - 32

32

U n i t i Introduction

New plant and animal species develop. Others become extinct. Fires, insects,
or diseases destroy a forest. Grasses and brush replace the forest, only to be
replaced eventually by a new forest.
As stated earlier, people change things. We clear forests, plow fields, drain
swamps, and build cities and highways. Such massive changes in the ecosystems
affect every living thing, including humans. It is because of this truism that books
such as this one are written.
Managing our natural resources wisely means, among many other things, controlling nature so that we can use its resources without destroying its balance (actually, its relative stability), or at least without permanently upsetting that balance.

Food Webs
All living things make up parts of both food chains and food webs. In its simplest
form, a food chain is a sequence of organisms, each of which provides a source of
nutrients for the next organism in the chain. A food web is a set of overlapping
food chains. Let's examine a couple of simple food chains and then see how they
could overlap to form a simple food web.

Fox

Food Chain

A plant seed germinates. It uses nutrients from the soil and air to grow. Later, the
plant's leaves and seeds are eaten by a grasshopper. A mouse makes a meal of the
grasshopper. Still later, one of the mice is eaten by a fox. In an ecological sense,
the plant is the producer, the grasshopper is the primary consumer, the mouse
is the secondary consumer and the fox is the tertiary consumer (Figure 3-7). We
sometimes talk about something being at the bottom or the top of the food chain
In this food chain, the plant is at the bottom and the fox is at the top.

Food Web

Rat

We know that life is more complex that a simple food chain. Mice also eat plant
materials, grubs, worms, and just about anything else they can get. Foxes are not the
only animals that eat mice-snakes, cats, and hawks make pretty effective mousers,
for instance. Small birds eat insects and plant seeds. Snakes, small predators like
cats, ferrets, and hawks eat small birds. Even larger predators like wolves and cougars catch and eat mice, small birds, and foxes. Deer eat plants and large predators
like wolves and cougars eat deer. All of these represent a set of many simple food
chains that make not only a much more complex, but also a more realistic food web
(Figure 3-8). In this ecosystem, the wolf and hawk would be referred to as apex
predators because they are at the top of the food chains that make up the food web.
In fact, from an ecological perspective, the food web just described was not
quite complete. The wolf and the hawk in their own turn will die and the nutrients from their bodies will return to the food chain to nourish the next generation
of grasses and trees. Moreover, not all food chains contain predators at the top,
like the hawk or wolf.

Plant

FIguRE 3-7 Food chains

Ā© Cengage LearningĀ®

Grasshopper

represent a simplified way of
looking at the connections
between producers and
consumers.

invasive Species
We have seen that all ecosystems are dynamic (changing). We have seen that a
balanced ecosystem is one that changes slowly enough that its plants and animals
have time to adapt. Drastic changes in the non-living (abiotic) parts of the ecosystem can upset that "balance." Flooding, rapidly warming local temperatures,
droughts, major storms, and the like are examples. But changes in the living
(biotic) parts of the ecosystem can also upset that "balance." New diseases are
one example of such a change. Another kind of biotic change has become more
important in recent years: invasive species.



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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