Naturalists and casual observers alike have been struck by the special relationship between squirrels and acorns (the seeds of oak trees). Ecologists, though, cannot observe these energetic mammals scurrying up and down oak trees and eating and burying acorns without wondering about their complex relationship with trees. Are squirrels dispersers and planters of oak forests or pesky seed predators? The answer is not simple. Squirrels may devour many acorns, but by storing and failing to recover up to 74 percent of them as they do when seeds are abundant, these arboreal rodents can also aid regeneration and dispersal of the oaks.
Their destructive powers are well documented. According to one report, squirrels destroyed tens of thousands of fallen acorns from an oak stand on the University of Indiana campus. A professor there estimated that each of the large white oaks had produced between two and eight thousand acorns, but within weeks of seed maturity, hardly an intact acorn could be found among the fallen leaves. Deer, turkey, wild pigs, and bears also feed heavily on acorns, but do not store them, and are therefore of no benefit to the trees. Flying squirrels, chipmunks, and mice are also unlikely to promote tree dispersal, as they often store seeds in tree cavities and underground burrows. Only squirrels - whose behavior of caching (hiding) acorns below the leaf litter - often promote successful germination of acorns, and perhaps blue jays, important long-distance dispersers, seem to help oaks spread and reproduce.
Among squirrels, though, there is a particularly puzzling behavior pattern. Squirrels pry off the caps of acorns, bite through the shells to get at the nutritious inner kernels, and then discard them half-eaten. The ground under towering oaks is often littered with thousands of half-eaten acorns, each one only bitten from the top. Why would any animal waste so much time and energy and risk exposure to such predators as red-tail hawks only to leave a large part of each acorn uneaten? While research is not conclusive at this point, one thing that is certain is that squirrels do hide some of the uneaten portions, and these acorn halves, many of which contain the seeds, may later germinate.
1. What does the passage mainly discuss?
(A) The ecology of oak trees
(B) Factors that determine the feeding habits of Squirrels
(C) Various species of animals that promote the dispersal of tree seeds
(D) The relationship between squirrels and oak trees
2. The word they in line 7 refers to
(A) oak forests
3. According to the passage , what do squirrels do when large quantities of acorns are available?
(A) They do not store acorns.
(B) They eat more than 74 percent of available acorns.
(C) They do not retrieve all the acorns that they have stored.
(D) They hide acorns in tree cavities.
Scientists have discovered that for the last 160,000 years, at least, there has been a consistent relationship between the amount of carbon dioxide in the air and the average temperature of the planet. The importance of carbon dioxide in regulating the Earth's temperature was confirmed by scientists working in eastern Antarctica. Drilling down into a glacier, they extracted a mile-long cylinder of ice from the hole. The glacier had formed as layer upon layer of snow accumulated year after year. Thus drilling into the ice was tantamount to drilling back through time.
The deepest sections of the core are composed of water that fell as snow 160,000 years ago. Scientists in Grenoble, France, fractured portions of the core and measured the composition of ancient air released from bubbles in the ice. Instruments were used to measure the ratio of certain isotopes in the frozen water to get an idea of the prevailing atmospheric temperature at the time when that particular bit of water became locked in the glacier.
The result is a remarkable unbroken record of temperature and of atmospheric levels of carbon dioxide. Almost every time the chill of an ice age descended on the planet, carbon dioxide levels dropped. When the global temperature dropped 9 F (5 C°), carb°on dioxide levels dropped to 190 parts per million or so. Generally, as each ice age ended and the Earth basked in a warm interglacial period, carbon dioxide levels were around 280 parts per million. Through the 160,000 years of that ice record, the level of carbon dioxide in the atmosphere fluctuated between 190 and 280 parts per million, but never rose much higher-until the Industrial Revolution beginning in the eighteenth century and continuing today.
There is indirect evidence that the link between carbon dioxide levels and global temperature change goes back much further than the glacial record. Carbon dioxide levels may have been much greater than the current concentration during the Carboniferous period, 360 to 285 million years ago. The period was named for a profusion of plant life whose buried remains produced a large fraction of the coal deposits that are being brought to the surface and burned today.
1. Which of the following does the passage mainly discuss?
(A) Chemical causes of ice ages
(B) Techniques for studying ancient layers of ice in glaciers
(C) Evidence of a relationship between levels of carbon dioxide and global temperature
(D) Effects of plant life on carbon dioxide levels in the atmosphere
2. The word accumulated in line 6 is closest in meaning to.
(A) spread out
(C) became denser
(D) built up
3. According to the passage , the drilling of the glacier in eastern Antarctica was important
(A) allowed scientists to experiment with new drilling techniques
(B) permitted the study of surface temperatures in an ice-covered region of Earth
(C) provided insight about climate conditions in earlier periods
(D) confirmed earlier findings about how glaciers are formed