Passage 46
Our study revealed that nest-guarding long-tailed skinks (a species of lizard) homed (returned to their nests) more successfully when displaced shorter distances. There are two reasons why homing success rates decreased with increasing displacement distance. One possibility is that females were simply displaced too far to find their way home. However, this is unlikely given that some individuals managed to find their way home from each distance we used. The second possibility deals with trade-offs between the risks associated with making a long return trip and the benefits of returning. Animals should expend energy only when the associated costs are low. As reptiles increase the time spent moving, their daily energy expenditure increases dramatically. The energetic costs of returning home and the chances that the eggs will have been preyed upon during the return trip both increase substantially as displacement distance increases. For example, the 130 hours (5.5 days) that female skinks spent returning from a distance of 300 meters is sufficient for an egg-eating snake to locate and prey upon the entire clutch. However, females with larger clutches were more likely to home at distances over 50 meters. For these females, the relative fitness benefits associated with having more eggs successfully hatch may outweigh the energetic costs of returning to a nest site, even if the nest may have already been preyed upon.
1. The primary purpose of the passage is to
A. question the validity of research on nest-guarding behavior in long-tailed skinks
B. consider explanations for a finding regarding long-tailed skinks
C. discuss the importance of homing for long-tailed skinks
D. describe the relationship between clutch size and homing success in long-tailed skinks
E. identify the benefits of a behavior common among long-tailed skinks
2. The claim in the highlighted sentence assumes which of the following about the individuals that managed to find their way home from each distance?
A. They were less able to detect egg-eating predators than were the other long-tailed skinks studied.
B. They were more averse to risk than were the other long-tailed skinks studied
C. They expended less energy when homing than did the other long-tailed skinks studied.
D. They did not possess better homing skills than did the other long-tailed skinks studied.
E. They had significantly smaller clutches than did the other long-tailed skinks studied.
3. The "second possibility" implies which of the following as a possible explanation for the female long-tailed skinks that failed to home from distances over 50 meters ?
A. They had relatively small clutches
B. They were unable to find their way home
C. They lacked sufficient energy to home successfully
D. They had male long-tailed skinks guarding their clutches
E. They detected evidence of egg-eating snakes In the vicinity of their nests.
答案： B D A