ACT science practice test 35

Directions: Each passage is followed by several questions. After reading a passage, choose the best answer to each question and fill in the corresponding oval on your answer document. You may refer to the passages as often as necessary.

You are NOT permitted to use a calculator on this test.


Shebay Park has been the site of ongoing population dynamics studies since the 1960s. Consisting of a group of isolated islands, the park provides ecologists with a unique, closed ecosystem in which to analyze the relationship between predator and prey populations. Figure 4.5 illustrates the food web for the Shebay Park ecosystem.

Figure 4.5

Ecological research in the park has focused mainly on the predator-prey relationship between the jaguar and peccary (a type of pig) populations. In addition to the typical selective pressures each species exerts on the other, scientists have observed specific events over the years that have affected population sizes. The inadvertent introduction of feline leukemia by humans in the late 1980s severely reduced the jaguar population. In 2004, the severest winter on record and an outbreak of ticks did the same to the peccary population. Figure 4.6 compares the annual population sizes for both species observed between 1968 and 2012.

Figure 4.6

1. Shebay Park is considered a closed ecosystem because:

A. organisms cannot easily migrate in from other ecosystems.
B. population sizes within the ecosystem do not fluctuate.
C. scientists have never had the opportunity to study the ecosystem.
D. predator-prey is the only type of relationship that exists in the ecosystem.

2. According to the food web in Figure 4.5, peccary can be categorized as which type of consumer?

A. Scavengers
B. Herbivores
C. Carnivores
D. Omnivores

3. According to Figure 4.6, what has been the maximum size of the jaguar population since 1968?

A. 20
B. 60
C. 50
D. 10

4. The peccary population reached its smallest size in which year?

A. 2006
B. 2003
C. 1995
D. 1988

5. It can be inferred that the 13-year trend in the peccary population that began after 1990 was largely influenced by a sharp decline in:

A. the jaguar population caused by disease.
B. cactus growth caused by disease.
C. the jaguar population during a severe winter.
D. cactus growth during a severe winter.

6. According to Figure 4.5, how many secondary consumer species are present in the Shebay Park ecosystem?

A. 0
B. 1
C. 6
D. 2

7. Organisms that compete for many of the same resources within an ecosystem are said to occupy similar niches. Based on the information in Figure 4.5, which populations occupy a niche most similar to that of the peccary population?

A. Nutria and squirrel
B. Fox and jaguar
C. Duck and fox
D. Nutria and duck

8. Based on the data in Figure 4.6, a sharp decline in a population's size most commonly occurs in response to:

A. a sharp increase in another population's size.
B. an event that reduces individuals' immediate survival.
C. a parallel decline in the size of other populations.
D. an event that limits individuals' reproductive ability.

9. Ecologists believe that an increase in parasites is partially responsible for the shift in:

A. the peccary population after 2004.
B. the peccary population before 2004.
C. the jaguar population after 1990.
D. the jaguar population before 1990.

10. Which of the following statements is best supported by the information in the passage?

A. Predation is the single greatest factor affecting peccary population size.
B. Food availability is the single greatest factor affecting peccary population size.
C. Peccary population size varies independently of the predator population size.
D. Predation is one of several factors that impact the size of the peccary population.

11. Based on Figure 4.5, which population is least likely to be affected by a change in the peccary population?

A. Aquatic plants
B. Squirrel
C. Cacti
D. Duck