III. Prepositions
Fill in the correct preposition for each blank space.
Much more abundant and ecologically important popula tion control are a huge diversity parasitic organisms. These or ganisms range tapeworms, which may be a foot or more
length microscopic disease-causing protozoans, fungi, bacte ria, and viruses. All species plants, animals, and even microbes
may be infected parasites. terms population bal ance, parasitic organisms act the same way large preda tors. As the population density the host organism increases,
parasites and their vectors (agents that carry the parasites one
host another), such disease-carrying insects, have little
trouble finding new hosts, and infection rates increase, causing die- back. Conversely, when the population density the host is low,
transfer infection is impeded, and there is a great reduction
levels infection, a condition that allows the population
to recover.
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Eight
IV. Definite/indefinite articles
Use a/an or the where needed. If no article is needed, write an .Yin the blank space.
In all such balances, however, whether simple or complex,
it is extremely important to recognize that high degree of
adaptation is involved on part of both prey or
host and natural enemy. This adaptation is such that
given natural enemy is incapable of completely eliminating its
prey or host population to certain density. Putting any
predator and prey or host and parasite
together does not lead to automatic balance. Such lack
of balance is shown all too clearly by what may occur when
species from one region is introduced into an other. Such introductions may lead to what are commonly called
ecological disasters as balances fail.
V. Values discussion
Answer the following questions. Then discuss your answers with your classmates.
1. What is the main idea of the article?
a. There are some specific mechanisms that provide population balance in nature.
b. Much more abundant and ecologically important in popula tion control are a huge diversity of parasitic organisms.
с All species of plants, animals, and even microbes may be infected by parasites, d. other
2. How are all of the mechanisms working in natural ecosystems?
a. In concert to provide population balance.
b. Separately to avoid consequences that may result, с In concert to create the overall balance.
d. other
3. What can each hare find when the hare population is low?
a. less food
b. plenty of places to hide and raise offspring с abundant food
d. other
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4. What does each hare have as the hare population increases?
a. fewer hiding places с abundant food
b. relatively less food d. other
5. Why does hunting become harder for the lynx?
a. Surviving hares are healthiest.
b. Surviving hares are best able to escape from the lynx, с Surviving hares starve.
d. other
6. How do parasitic organisms range?
a. tapeworms
b. microscopic disease-causing protozoans с viruses
d. other
7. When do infection rates increase, causing dieback?
a. As the population density of the host organism increases.
b. When the population density of the host is low.
с When parasites and their vectors have little trouble finding new
hosts, d. other
8. What may parasites do with their host?
a. kill it с make it more vulnerable
b. weaken it d. other
9. What are balances between an organism and several natural ene mies?
a. much more stable с less prone to wide fluctuations
b. unstable d. other
10. What is a high degree of adaptation involved on?
a. the part of the prey с the part of the host
b. the natural enemy d. other
11. What is a given natural enemy capable of?
a. limiting the prey population
b. limiting the host population
с completely eliminating its prey or host d. other
12. What may occur when a species from one region is introduced into another?
a. an automatic balance
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106 Unit Eight
Ecosystems: Mechanisms of Population Balance
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b. a certain density of host population .¥
c. ecological disasters
d. other
13. What another factor is often involved in the control of carnivofb and some herbivore populations?
a. some species с excess carnivore population
b. territoriality d. other
14. What is the size of the territory defended?
a. small с depends on resources available
b. large enough d. other
15. What mechanisms does territoriality create in the face of limited resources?
a. of selecting the strongest and fittest
b. of eliminating the genes of the weaker individuals с of surviving and breeding
d. other
16. What do nations continue to arm themselves to the teeth with?
a. a fence
b. the most sophisticated weaponry available с a piece of land
d. other
17. Are humans also a territorial animal?
a. no с to an extent that greatly exceeds any other species
b. yes d. other