Use the following information to answer questions 20 and 21:

a team of ecologists measured the salinity of the water in an estuary at various distances from the river mouth. they also sampled populations of two species of clam worm, nereis occidentalis and neanthes succinea, at each point. the results are tabulated in the following table.

nereis occidentalis
(no. per 100 cm2)

3

11

19

33

42

61

neanthes succinea
(no. per 100 cm2)

57

41

36

17

9

3

distance from the river
mouth (meters)

0

10

20

30

40

50

salinity (%)

0

5

9

14

21

30

20. which of the following hypotheses is most valuable in explaining the trends seen in the data?

a. nereis occidentalis outcompetes neanthes succinea at salinities under 14%.
b. neanthes succinea reproduces most rapidly in areas at least 20 meters from the river mouth.
c. both neanthes succinea and nereis occidentalis can survive at any salinity level.
d. nereis occidentalis is more resistant to salinity than neanthes succinea.

21. if the ecologists were to take a population sample of neanthes succinea in an area 65 meters from the river mouth with 30% salinity, what do you infer that they would find?

a. 40-50 individuals
b. 10-20 individuals
c. fewer than 5 individuals
d. more than 50 individuals

22. some coral reefs off the east coast of south america are starting to die off. satellite images reveal great plumes of sediment washing out of the mouths of rivers. what can you conclude, if anything, about the relationship between these two factors?

a. although the two factors coincide, they are not likely to be related.
b. deforestation on land results in lower oxygen levels in the atmosphere, which stresses the reefs.
c. deforestation on land allows erosion to wash away topsoil, creating sediment which smothers the reefs.
d. burning of the rain forest increases atmospheric carbon dioxide to levels toxic to reefs.

23. what is the distinction between a range of tolerance and limiting factors?

a. limiting factors are biotic or abiotic factors that limit the growth of a species, while the range of tolerance defines the set of conditions in which an organism can survive.
b. the range of tolerance defines biotic or abiotic factors that limit the growth of a species, while limiting factors define the set of conditions in which an organism can survive.
c. limiting factors and zones of tolerance are two terms for the same concepts about species survival under various environmental conditions.
d. limiting factors are biotic features only, such as interactions with other life forms, that limit a species, while range of tolerance is based only on abiotic conditions.

24. which of the following does not affect the spatial distribution of a population?

a. the carrying capacity of a population
b. the distribution of food and other resources
c. abiotic conditions such as rainfall and sunlight
d. the existence of predators or parasites

25. which of the following statements is correct?

a. population size of predators increases when their prey is scarce.
b. competition for resources is density-independent when food is plentiful.
c. disease is density-dependent because transmission occurs more easily when a population is large.
d. a change in average temperature is a density-dependent factor because fewer organisms can acclimate to variations in temperature.

26. how does the logistic model of population growth differ from the exponential model?

a. the exponential model shows a restricted growth rate.
b. the logistic model considers the environment’s carrying capacity.
c. the graph of the exponential model is s shaped.
d. the graph of the logistic model has a longer lag phase.

27. a fruit fly that has a short life span and produces many offspring can be classified into which reproductive strategy?

a. r-strategist
b. k-strategist
c. a carrying-capacity strategist
d. a logistic strategist

28. which characteristic is typical of a k-strategist?

a. short life span
b. generally a small organism
c. produces many offspring
d. lengthy parental care

29. which of the following methods might be used to decrease the rate of approach to carrying capacity by the developed world?

a. increase birthrate
b. decrease death rate
c. decrease resource use
d. decrease emigration