II. Vocabulary
From the list of words and expressions below, choose the correct word or expression for each blank space. Use each word or expression only once.
stages adults recruitment pack of wolves
refer to recover boil down exponential increase
explosion reproducing rule out herd of deer
fluctuate interbreeding birthrate relative phenomenon
foresee population replacement level school offish
mitigate death rate flack of birds biotic potential
1. Each species in an ecosystem exists as a — that is to say, an
, group.
2. Thus, the problem of ecosystem balance to a problem of
how or are balanced for each species in the ecosys tem.
3. , which is defined as making it through the early growth
to become part of breeding, reproducing population, is
equally important.
All these factors taken together are as the of the species.
Such a multiplying series is called an .
In populations it is commonly called a population .
One may already the result of the interplay between biotic
potential and environmental resistance.
Of course, some also perish, particularly the old and weak.
If recruitment is at the , just enough to replace these adults,
then the population size will remain constant.
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Unit Seven
Ecosystems: What Keeps Them the Same?
91
It
should be noted that balance is a .
Some balances very little, others widely.
Indeed, in nature, neither possibility is .
Conversely, as population density decreases, environmental resistance is generally , allowing the population to .
Furthermore, the biotic potential of many species depends on a
minimum population base a , a , a , or
a , for example.
III. PREPOSITIONS Fill in the correct preposition for each blank space.
The one thing that enables ecosystems to sustain a given composition species long periods time is that all relationships the system are a dynamic balance.
An ecosystem's remaining stable a long period time
implies that the population each species the ecosys tem remains more or less constant size and geographic dis tribution.
3. other words, most the young fish and plants perish
the early stages growth.
Populations natural ecosystems do not explode because all conditions are seldom favorable any extended period time.
Sooner or later, any population increase will be curtailed
one or more factors environmental resistance.
6. general, the reproductive rate a species remains fair ly constant because that rate is part the genetic endowment
the species.
7. example, loss suitable habitat often prevents animals
breeding.
8. What prevents a population going an explosion or
extinction?
9. general, populations remain a certain size range be cause most factors environmental resistance are density- dependent. 10. Human impacts, the other hand, readily result ex tinction because they are not density-dependent.
11. Furthermore, the biotic potential many species depends
a minimum population base a herd deer, a
pack wolves, a flock birds, or a school fish,
example.
IV. DEFINITE/INDEFINITE ARTICLES
Use a/an or the where needed. If no article is needed, write an A* in the blank space.
Each species in ecosystem exists as population - that
is to say, interbreeding, reproducing group. eco system's remaining stable over long period of time im plies that population of each species in ecosys tem remains more or less constant in size and geographic
distribution. Any continuing increase or decrease in popula tion would be observed as change in ecosystem. In turn,
population's remaining constant over long time
means that reproductive rate is equaled by death rate.
Thus, problem of ecosystem balance boils down to
problem of how birth rate and death rate are balanced
for each species in ecosystem.