Chapter 13 Ecological Principles • MHR 463MAKING CONNECTIONS15.A famous ecologist once wrote a book called
The Ecological Theater and the Evolutionary
Play. What do you think he meant by this title?
Write a paragraph explaining this title and
discussing the relationship between
evolutionary and ecological change.
16.Nature’s most unusual organisms are generally
found in extreme environments (such as
deserts, the Arctic, or at the bottom of oceans).
To many people, these organisms are so
anatomically different that they appear
grotesque. They are also often physiologically
different from organisms we are more familiar
with. What reasons can you give for this
phenomenon?
17.Why do some species have small ranges? Part
of the answer to this question lies in this
chapter. Can you think of any other factors that
might contribute to limiting the geographic
distribution of a species to a very small area —
usually on one continent?
18.When asked to describe the difference between
plants and animals, many students answer that
photosynthesis only occurs in plants and
cellular respiration only occurs in animals.
What is wrong with this statement? Why do
you think this is a source of confusion for
students? What might you do to reduce the
problem (that is, to make the facts clearer and
more memorable)?
19.Scientists have discovered that the rates of
decomposition in ecosystems vary from an
average of four to six years in tropical forests to
50 years in the tundra. This means that there is
little decaying matter (leaf litter) containing
nutrients on the ground in tropical forests.
Instead, the nutrients are taken up very quickly
by rapidly growing trees, with only about
10 percent of the nutrients existing in the soil.
Seventy-five percent of the nutrients in a
tropical forest ecosystem are contained in the
woody trunks of the trees. On the other hand,
50 percent of the nutrients in a temperate forest
ecosystem may be present in the soil and leaf
litter. How do you think these two types of
ecosystems differ with respect to their ability
to withstand logging? Explain your answer in
full, addressing any differences in the process
of secondary succession that you might see
between the two.
20.Many of the endangered species in the world
are specialist species, with narrow ecological
niches. Why is this?
21.Many of the world’s top carnivores are also
endangered. Why do you think this is so?
22.Grizzly bears (Ursus horribilus) and Gray
wolves (Canis lupus) are top predators in
various ecosystems, and were extirpated (that
is, they went extinct locally) between 60 and
150 years ago in parts of their range. As a
result, moose populations in these areas grew
rapidly. Researchers have found that in some
locations, human hunters replaced grizzlies
and wolves as a top predator and reduced
moose densities. In areas where hunting was
not permitted, moose numbers remained so
high that the pressure of their grazing
(particularly on shrubs along the shores of
lakes and streams) reduced the density of the
plants in these habitats. This in turn had an
impact on birds, which had previously used
these shorelines for nesting or resting spots
during migration, and certain bird species
disappeared entirely. To some ecologists, these
results showed that the structure of certain
communities is determined from the “top
down” by predators, rather than from the
“bottom up” by the type and density of plants.
They argue that this shows how vital it is to
re-introduce grizzlies and wolves into areas
where they have disappeared, and to ensure
they are conserved where they still exist. Do
you agree? Pretend that you are attending a
public meeting discussing the possibility of
re-introducing wolves to an area near your
community. What will you say to the scientists
proposing the re-introduction?about the issue. Explain your position in a
one-page essay.14.Over a two-week period, collect newspaper
items that describe or cover what might be
called environmental issues. (Alternatively,
do a web search and research a single topic
that spans a two-year period.) For each article
or topic, list the concepts from this chapter
(refer to the Language of Biology list) that relate
to the story or issue described.