CHAPTER 21 Test Your Knowledge

Driving Question 1

By answering the questions below and studying Infographics 21.1, 21.2, and 21.3, you should be able to generate an answer for the broader Driving Question above.

KNOW IT

What is the difference between a community and a population?

An ecosystem ecologist might study
a. plant populations.

b. herbivores that eat the plants.

c. predators in the population.

d. the impact of precipitation patterns on the plant populations.

e. all of the above

Why do the researchers collect scat as part of their study on Isle Royale?

USE IT

How would you explain to a 10-year-old what ecologists do?

Your local environmental group wants to determine the population size of squirrels in a nearby nature preserve. What are some methods you could use to estimate the size of the squirrel population? Would the same approaches be as useful in determining the population size of maple trees in the same area? Why or why not?

How would you use scat analysis to determine whether an herbivore had a preference for a particular type of vegetation? Be specific about both the type of analysis and what the analysis would reveal for herbivores with or without a preference for a particular type of vegetation.

Driving Question 2

By answering the questions below and studying Infographic 21.4, you should be able to generate an answer for the broader Driving Question above.

KNOW IT

Which of the following would cause a population to grow?
a. identical increases in both the birth rate and the death rate of a population

b. a decrease in the birth rate and an increase in the death rate of a population

c. an increase in the birth rate and a decrease in the death rate of a population

d. an increase in the birth rate and a larger increase in the death rate of a population

e. an identical decrease in both the birth rate and the death rate of the population

Which of the following statements describes an example of population growth?
a. The average weight of Americans has increased substantially in the past decade.

b. Tropical fish have been found in waters more northerly than their usual habitat.

c. The number of people in a town has increased by 25% in the past 5 years.

d. The number of butterflies in a region has stayed the same from 1950 to 2010.

e. all of the above

When a population reaches its carrying capacity, what happens to its growth rate?

USE IT

The wolf population on Isle Royale in 2013 was eight. There was no evidence of wolf reproduction in 2013.
a. What is the current birth rate for the wolf population?

b. If the death rate for wolves is 1 per year, what will be the size of the wolf population in 2014, assuming the birth and death rates do not change?

c. If the winter of 2015 is very cold and an ice bridge linking Isle Royale and the mainland forms, what factor could contribute to growth of the wolf population?

Driving Question 3

By answering the questions below and studying Infographics 21.5, 21.6, 21.7. 21.8, and 21.9, you should be able to generate an answer for the broader Driving Question above.

KNOW IT

The Mexican gray wolf has been reintroduced into parts of New Mexico and Arizona. There have been several wolf deaths due to shootings and traffic kills. Are these influences on the wolf population biotic or abiotic factors?

Drought causes a pond to dry up almost completely. The frog population dropped to 10% of its initial size. What kind of factor—biotic or abiotic—influenced the frog population?

Which of the following is a density-dependent factor influencing population growth?
a. elevated temperature

b. prolonged winters

c. a viral disease

d. a devastating forest fire

e. all of the above

USE IT

Why is it important for researchers to determine the cause of death of moose on Isle Royale? Can this information be used to help make predictions about moose and wolf populations? Explain your answer.

A group of predatory fish lives in a school in a large lake. If a parasite were introduced to the lake—for example by a vacationing fisherman—would you expect it to have a greater impact on the population if the fish were at high density or at low density? (Assume the parasite is passed from one fish to another through the water but can remain alive in the water only for a very short period of time.) What would happen to this same population if there were a severe drought and very hot summer?

Classify each of the following as a biotic or an abiotic factor in an ecosystem. Then predict the impact of each factor on the moose population of Isle Royale. Explain your answers, keeping in mind possible interactions between the various factors and between the moose and wolf populations.
a. hot summer temperatures

b. ticks that parasitize moose

c. declining numbers of balsam fir trees

d. a parvovirus in wolves

e. deep winter snowfall

Assume that a new herbivore is added to Isle Royale that is not a prey for wolves. Predict the effect of this introduction on
a. the populations of trees.

b. the moose population.

c. the wolf population.

If the moose population remains stable, what other factors could influence the wolf population on Isle Royale?