Useful words and expressions

paragraph 1	paragraph 4	paragraph 7
relationships	additional	vulnerable to predation
	ability	adults
paragraph 2	disperse	replacement level
population	defense mechanisms	losses
interbreeding group	resistance
reproducing group	adverse conditions	paragraph 8
distribution	refer to	shifts
reproductive rate	biotic potential	relative phenomenon
birth rate	reproductive capacity	fluctuate
death rate	generation	rule out
boil down	female
	rabbits	paragraph 9
paragraph 3	offspring	density-dependent
maintain	exponential increase	per unit area
seeds	explosion	mitigate
spores		recover
recruitment	paragraph 5
stages	predators	paragraph 10
nil		herd of deer
perish	paragraph 6	pack of wolves
mortality	foresee	flock of birds
conversely	curtail	school offish
relatively	genetic endowment EXERCISES	habitat alteration threatened endangered

I. Reading comprehension

1. What is the main idea of the article?

a. One may already foresee the result of the interplay between bio­tic potential and environmental resistance.

88

Unit Seven

Ecosystems: What Keeps Them the Same?

89

b. No forces or rigid structures exist that prevent ecosystems from

changing, с Human impacts readily result in extinction because they are

not density-dependent.

2. Each species in an ecosystem exists as

a. a population

b. an interbreeding group с reproductive rate

3. Maintaining or increasing a population depends on

a. recruitment

b. reproductive rate

с the early growth stages

4. The biotic potential of the species is referred to as

a. the ability of animals to migrate

b. defense mechanisms

с resistance to adverse conditions and disease

5. Environmental resistance is referred to as

a. one or more abiotic factors

b. one or more biotic factors

с the combination of all abiotic and biotic factors that may limit population increase

6. Environmental resistance effectively reduces

a. any population increase

b. the replacement level с recruitment

7. In certain situations environmental resistance may

a. cause mortality

b. effect reproduction

с block a population's growth

8. The result of a dynamic balance between population's biotic po­ tential and environmental balance is

a. biotic potential remains constant

b. a population growth remains stable с a population growth decreases

9. Populations remain within a certain size range because <

a. population growth ceases or declines

b. environmental resistance becomes more intense

с most factors of environmental resistance are density-depen­dent

10. Human impacts result in

a. ecosystem destruction

b. habitat alteration с extinction

11. The biotic potential of many species depends on

a. a pack of wolves

b. a school offish

с a minimum population base