ACT Reading Dec. 2015 72E - Passage IV

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
₅ cones-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
₁₀ can'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.

₁₅ Sometimes 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
₂₀ must 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
₂₅ cool 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
₃₀ guarding 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,
₃₅ in 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
₄₀ species. 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
₄₅ the 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,
₅₀ incorporating 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
₅₅ biogeographical?

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
₆₀ student 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
₆₅ to 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
₇₀ very 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
₇₅ tended 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
₈₀ hotter 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
₈₅ air 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."