ACT Reading Practice Test 90: NATURAL SCIENCE

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.


NATURAL SCIENCE: This passage is adapted from the article "Silence of the Pikas" by Wendee Holtcamp (©2010 by Wendee Holtcamp).

Pikas, a diminutive alpine-dwelling rabbit relative,
are unique among alpine mammals in that they gather
up vegetation throughout summer-including flowers,
grasses, leaves, evergreen needles, and even pine
5cones-and live off the hay pile throughout winter,
rather than hibernating or moving downslope. But
increasingly warm temperatures may drive them to the
brink: the high-energy mammals can overheat and die
at temperatures as mild as 25 degrees Celsius if they
10can't regulate their body temperature by moving into
the cooler microclimate under the talus. And since they
already live near the tops of mountains, when a particu-
lar talus field's microclimate becomes inhospitable,
they simply have nowhere to go.

15Sometimes called cony. mouse hare, rock rabbit.
or whistling hare; the pika has a narrow niche. They
live only in talus fields, and these must lie adjacent to
alpine meadows or other vegetation so they have access
to plants for food and hay farming. The talus rock fields
20must have boulders of a certain size; scree, a similar
habitat with smaller rocks, won't do. Rocks provide
safe haven from pikas' main predator, weasels. But per-
haps more important, the interstices between the rocks
provide both a cool, moist microclimate where pikas
25cool down during hot summer days and also the perfect
sanctuary in which to settle during the long winter's
night. They don't huddle together like many other
mammals, as far as scientists can tell, but remain
fiercely territorial and solitary throughout the winter
30guarding their hay piles with their lives. As a snowpack
settles over the land, it insulates the Earth and main-
tains a certain underground temperature at which pikas
can survive, Just below freezing. With warming temper-
atures reducing snowpack in many mountainous areas,
35in a strange twist of fate, global warming can cause
pikas to freeze

Biologists have dubbed mountaintop habitat
patches "sty islands" because the valleys in between
are as uninhabitable as the sea for nonmobile alpine
40species. This creates an ideal scenario to test the pre-
dictions of one of ecology's key theories: island bio-
geography. Individual pikas have a relatively limited
distance they can disperse, around two kilometers, so
they can't just shift from one mountain to another. At
45the population level, they're stuck on a particular
mountain range. In the 1990s, biologist Erik Beever and
colleagues surveyed pikas throughout the hydrographic
Great Basin-a heart-shaped 500,000 square kilometer
intermontane plateau dotted with 314 mountain ranges,
50incorporating parts of California, Nevada, Utah,
Oregon, Idaho and Arizona-and were unable to find
pikas in 6 of 2S mountain ranges that they had occupied
in the late 20th century. Was the cause of pika extirpa-
tions (disappearances) climatic, anthropogenic. or
55biogeographical?

Island biogeography theory says that "species are
predicted to remain on large islands and islands that are
not very isolated from mainland [habitat]," explains
Beever, who did much of his work while a graduate
60student under Mary Peacock, at the University of
Nevada-Reno. He and colleagues found pika popula-
tions persisted in mountain ranges with more talus
habitat available-supporting one prediction of island
biogeography theory-but pikas were not more likely
65to persist at sites closer to the Rocky Mountain or
Sierra Nevada "mainland" ranges.

"Here isolation doesn't have anything to do with
whether they're lost or not," Beever says, Not only that,
"the sheer size of a mountain range in this case isn't
70very predictive of patterns of loss. [And] if we count
the amount of habitat, that's less important than these
climatic influences." Ultimately. the factors most
strongly associated with pika disappearance were cli-
matic; specifically, warmer and drier sites, which
75tended to be lower down the mountains. In another
study published in Ecological Applications, Beever,
University of Colorado researcher Chris Ray. and other
colleagues revealed that acute cold stress and chronic
heat stress (in other words, cold snaps and overall
80hotter summers) affect pika more than individual very
hot days.

"The problem with global warming is that if
[pikas] lose [their] snowpack, which provides insula-
tion in winter, they freeze to death, and if the ambient
85air temperature heats up too much in summer, then they
[overheat]. That's the challenge," Peacock says, who
has studied pika population genetics. "They're already
at the top of the mountain. If you heat it up substan-
tially, there's no place for them to go."

1. The primary purpose of the passage is to discuss the:

A. methods scientists use to track the numbers of pikas in several regions.
B. role pika social behavior plays in their ability to adapt to changing conditions
C. causes of pika disappearances and scientists pro-posed solutions to the disappearances
D. habitat and conditions in which pikas flourish and the causes of their disappearances.

2. In lines 53-55, the author poses a question about the cause of pika disappearances that she:

F. answers in the paragraphs that follow.
G. uses to emphasize the extent of pika disappearances.
H. asks to highlight flaws in Beever's research.
J. poses to establish the three main results of pika disapperances.

3. According to the passage, one of Beever's findings that supports island biogeography theory is:

A. pika populations thrived in most of the mountain ranges that pikas had occupied in the twentieth century.
B. pika populations endured in mountain ranges with more talus habitat available.
C. the size of a mountain range correlated with the size of a pika population.
D. isolated pika populations were more likely to sur-vive in varied habitats.

4. According to the passage, the study published in Ecological Applications indicates that a pika population is most stressed by a summer with:

F. a higher than average amount of rainfall.
G. several individuai very hot days.
H. overall hotter temperatures.
J. slightly cooler temperatures.

5. It can most reasonably be inferred from the passage that one reason pikas easily overheat is that they:

A. become overwhelmed by a thick snowpack.
B. are a high-energy mammal.
C. huddle together in interstices.
D. insulate themselves inside hay piles.

6. The passage indicates that compared to a talus field scree habitats have:

F. more food.
G. fewer predators.
H. smaller rocks.
J. better access to interstices

7. The passage indicates that the perfect sanctuary for a pika on a long winter night is located

A. on a hay pile near an alpine talus field.
B. in an alpine meadow near a talus field.
C. on the top of a mountain adjacent to a talus field.
D. in the interstices between rocks in an alpine talus field.

8. In the passage. the behavior of pikas during winter is characterized in part as:

F. fiercely territorial.
G. relatively relaxed.
H. predatory.
J. social

9. The passage states that biologists dub mountaintop habitat patches "sky islands" because:

A. any species that survive on mountaintops are com-pletely cut off from the rest of the mountain
B. the mountaintops' altitude makes them a haven for most species.
C. the valleys between mountaintops are as uninhab-itable as the sea would be for nonmobile alpine species.
D. like the sea, mountaintops are only habitable to mobile species.

10. It can most reasonably be inferred from the passage that as compared to pika populations on the top of a mountain, those at lower mountain elevations are more likely to:

F. disappear.
G. thrive.
H. remain unchanged.
J. migrate to another mountain range