Botkin Environmental Science Earth as Living Planet 8th txtbk

86 CHAPTER 5 Ecosystems: Concepts and Fundamentals
A CLOSER LOOK 5.1
Land and Marine Food Webs
A Terrestrial Food Web
An example of terrestrial food webs and trophic levels is shown
in Figure 5.5 for an eastern temperate woodland of North
America. The first trophic level, autotrophs, includes grasses,
herbs, and trees. The second trophic level, herbivores, includes
mice, an insect called the pine borer, and other animals (such
as deer) not shown here. The third trophic level, carnivores,
includes foxes and wolves, hawks and other predatory birds,
spiders, and predatory insects. People, too, are involved as
omnivores (eaters of both plants and animals), feeding on
several trophic levels. In Figure 5.5, people would be included
in the fourth trophic level, the highest level in which they would
take part. Decomposers, such as bacteria and fungi, feed on
wastes and dead organisms of all trophic levels. Decomposers are
also shown here on the fourth level. (Here’s another interesting
question: Should we include people within this ecosystem’s food
web? That would place us within nature. Or should we place
people outside of the ecosystem, thus separate from nature?)
Red-tailed
hawk
IV
Sun
III
Golden-crowned
kinglet
Pine
borer
II
Oak
tree
IV
Snake
Oak
acorns
I
II
III
Pine
I
Simple
chemical
compounds
(phosphates,
nitrates, etc.)
Mouse
Salamander
Decomposers
Bacteria
Fungi
FIGURE 5.5 A typical temperate forest food web.