Prep2012_Pack1_RC(题目版)(19)

The author's argument that increased straying can “lower the overall fitness of subsequent generations” (see highlighted text) is based on which of the following assumptions?

A. A disturbance of salmonid spawning streams caused by human activity could increase the

straying rate of affected salmonid populations as much as the aftermath of the Mount Saint Helens eruption did.

B. In the streams in which the straying salmonid spawn, these straying salmonid would

amount to no more than 40 percent of the total spawning population.

C. Salmonid in some streams benefit from particular local adaptations.

D. Nonenvironmental factors have no effect on salmonid straying rates.

E. At least some of the streams in which straying salmonid would spawn are pristine,

affected by neither natural nor artificial disturbances.

PREP2012-Pack1-RC-008-05 VRC000460-07 Hard

Which of the following does the author mention as support for the view that environmental disturbances caused by human activity could increase straying rates?

A. The existence of salmon populations in rivers where the elimination of salmon habitat by

human activity had previously made the fish extinct

B. The results of studies measuring the impact on straying rates of habitat loss caused by

human activity

C. The potential for disturbances in one environment to cause the introduction of novel

genes into salmon populations in neighboring areas

D. The weaknesses in the view that the extinction of entire salmon populations is the only

mechanism by which human destruction of salmon habitat reduces genetic diversity in salmon

E. The absence of any reason for believing that disturbances brought about by human

activity would differ in their effects from comparable disturbances brought about by natural causes

PREP2012-Pack1-RC-009

The sloth bear, an insect-eating animal native to Nepal, exhibits only one behavior that is truly distinct from that of other bear species: the females carry their cubs (at least part-time) until the cubs are about nine months old, even though the cubs can walk on their own at six months. Cub-carrying also occurs among some other myrmecophagous (ant-eating)

mammals; therefore, one explanation is that cub-carrying is necessitated by myrmecophagy, since myrmecophagy entails a low metabolic rate and high energy expenditure in walking between food patches. However, although polar bears’ locomotion is similarly inefficient, polar bear cubs walk along with their mother. Furthermore, the daily movements of sloth bears and American black bears—which are similar in size to sloth bears and have

similar-sized home ranges—reveal similar travel rates and distances, suggesting that if black bear cubs are able to keep up with their mother, so too should sloth bear cubs.

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