The Sentinel Behavior of Meerkats

Paragraph 1：A species of small mongooses in Africa called meerkats share sentinel (guard) duties to warn other group members by repeating alarm calls if a predator is seen. This is an important job, because when meerkats are foraging, their heads are in the ground seeking prey, and they cannot see a predator coming. 

 

 

Paragraph 2：The question is, why do group members take turns acting as sentinels? Kin selection, that is, being able to save the lives of family members can be one hypothesis for this type of sentinel behavior. Family members share copies of a meerkat’s genes. Kin selection is achieved by helping a meerkat’s own offspring as well as non descendant kin, including sibling, nieces, nephews, aunts, and uncles. Therefore, if members of a certain group are closely related, a sentinel ensures that copies of its genes can be passed on to future generations by saving the majority of family members by alerting others, even at the expense of its own life. 

 

 

 

1. Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information.

 

(A) A sentinel attempts to save as many closely related family members as possible, even if it dies while doing so.  

 

(B) The group will not be able to pass their genes to future generations if a sentinel dies before alerting other family members.  

 

(C) The genes of all members of the group will be passed to future generations even if a sentinel alerts only its close family members.  

 

(D) Although a sentinel dies while alerting family members, it ensures that its genes will survive in future generations.

 

 

 

 

 

Paragraph 3：Assuming this hypothesis is true, we can predict that group members have close genetic ties. Otherwise, kin selection would not work. But this prediction does hold true. A dominant, breeding female is mother to 75 percent of all the litters in a group, and one dominant male fathers 75 percent of all the pups born. Even though a typical meerkat group includes a few immigrants, most subordinate adults are siblings or half siblings. Therefore, it is likely that subordinate adults share 25 or 50 percent of their genes. 

 

 

 

2. According to paragraph 3, the theory that meerkats’ sentinel behavior is the result of kin selection is supported by the fact that  

 

(A) sentinels warn the dominant males and females of the meerkat group first  

 

(B) most members of a meerkat group are hereditarily related to each other 

 

(C) immigrant members of the meerkat group will benefit from the sentinels’ warnings  

 

(D) only a small portion of a meerkat group serves as sentinels

 

 

Paragraph 4：On account of most meerkat group members being family, it is possible that kin selection has favored sentinel behavior. Nonetheless, by itself, a close inherent relationship is not enough evidence to conclude that kin selection has played a role. Thus, we need further evidence, and must improve the prediction. 

 

 

 

3. What role does paragraph 4 play in the passage?  

 

(A) It explains the difficulties in collecting evidence about kinship relationships.  

 

(B) It introduces a new hypothesis to replace the one presented in paragraph 2.  

 

(C) It explains the relationship between hypotheses, prediction, and evidence.  

 

(D) It introduces another observation test of the hypothesis presented in paragraph 2.

 

 

 

Paragraph 5：Based on the same hypothesis, a more specific prediction is that each mongoose should increase the frequency of sentinel behavior when they are guarding family members. This new prediction needed testing, so the group was observed to determine which members stand guard and when. The immigrants without any kin relations to other group members acted as sentinels just as much as the individuals with many relatives nearby. Therefore, the result of this test does not support the kin-selection hypothesis. 

 

 

 

4. Paragraph 5 suggests that before the more specific prediction based on the kin-selection hypothesis is tested, researchers involved in the testing should know  

 

(A) the minimum number of members needed as guards  

 

(B) which group members were related to each other 

 

(C) which group members were more skilled at standing guard  

 

(D) how well group members were protected by the sentinels

 

 

 

Paragraph 6：Another hypothesis that is often suggested to explain such cooperative behavior is that it results from reciprocal altruism — each individual takes turns standing guard to benefit the rest of the group, rather than itself. The reciprocal altruism theory can work only when those who cheat by avoiding guard duty can be identified and punished by the rest of the group. This hypothesis produces the prediction that there should be a regular rotation of sentry duty within the group and that the ones who neglect this duty should be chastised. However, this is not observed. In fact, the group members do take turns on sentry duty, but there is no predetermined order for this. In addition, when some members shorten their shift, other group members increase their contributions to compensate. The predictions and observations of the reciprocal-altruism hypothesis do not coincide with each other. 

 

 

 

5. According to paragraph 6, what observation was made that weakened the reciprocal-altruism hypothesis?  

 

(A) Some group members never spent any time guarding.

 

(B) There were some moments when no sentinel was present.  

 

(C) No established order of guard duty existed. 

 

(D) Some group members were less severely punished than others.

 

 

 

 

 

Paragraph 7：Yet another hypothesis for the evolution of meerkat sentinel behavior is that it results from selfish antipredator behavior. This idea stems from the fact that the meerkat watching for predators increases its personal safety, and warning others does not harbor any disadvantage. So, when a meerkat has had enough to eat, it should watch for predators. The sentinel on duty can then return to foraging. This hypothesis produces a prediction that sentinel duty is not dangerous or risky in any way. This does seem to be true. Over the course of 2,000 hours of observation, no sentinels were attacked or killed by predators. They may actually be safer because they are the first to sense the predator. Moreover, they generally stand guard within 5 meters of a burrow, and are the first underground when a predator comes close.  

 

 

 

6. According to the hypothesis discussed in paragraph 7, why would a meerkat choose to stand guard once it has eaten?  

 

(A) To look for new foraging grounds as well as predators  

 

(B) To protect itself from being attacked by a predator 

 

(C) To improve its position within the group  

 

(D) To warn others in its group of any predator attacks, even at great risk to itself

 

 

 

7. According to paragraph 7, the fact that during the 2,000 hours of observation no sentinels were attacked by predators may show that  

 

(A) sentinels are extremely effective in warning members of their group about dangers  

 

(B) it is safer for an individual to stand guard than to be guarded from predation 

 

(C) it is hard to determine how hard guard duty is even from 2,000 hours of observation  

 

(D) sentinels can ensure that foraging group members stay within 5 meters of a burrow

 

 

 

Paragraph 8：If a meerkat’s personal safety is increased with serving as a sentinel, it would be possible to predict that an individual would spend a proportion of its time guarding, whether it was solitary or part of a group. As predicted, individual meerkats spend about the same time on guard duty as members of large groups. Groups with more members suffer less predation because there is a sentinel for a longer portion of foraging time than in small groups.  

 

 

 

8. According to paragraph 8, which of the following statements is supported by studies of individual meerkats’ guarding behavior?  

 

(A) Solitary meerkats spend more time on foraging than ones belonging to a group, but they also watch for predators some of the time.  

 

(B) Individual animals in large groups tend to spend more time on guard duty than ones in small groups.  

 

(C) The time spent watching for predators increases a meerkat’s personal safety even when the animal is solitary. 

 

(D) Sentinels prefer to spend their guarding time as solitary individuals rather than as members of a large group.

 

 

 

 

 

Paragraph 7：Yet another hypothesis for the evolution of meerkat sentinel behavior is that it results from selfish antipredator behavior. This idea stems from the fact that the meerkat watching for predators increases its personal safety, and warning others does not harbor any disadvantage. So, when a meerkat has had enough to eat, it should watch for predators. The sentinel on duty can then return to foraging. This hypothesis produces a prediction that sentinel duty is not dangerous or risky in any way. This does seem to be true. Over the course of 2,000 hours of observation, no sentinels were attacked or killed by predators. They may actually be safer because they are the first to sense the predator. Moreover, they generally stand guard within 5 meters of a burrow, and are the first underground when a predator comes close. ■ 

 

 

 

Paragraph 8：If a meerkat’s personal safety is increased with serving as a sentinel, it would be possible to predict that an individual would spend a proportion of its time guarding, whether it was solitary or part of a group. ■ As predicted, individual meerkats spend about the same time on guard duty as members of large groups. ■ Groups with more members suffer less predation because there is a sentinel for a longer portion of foraging time than in small groups. ■ 

 

 

 

9. Look at the four squares [ ■ ] that indicate where the following sentence could be added to the passage.  

 

This results in meerkats gaining an advantage in survival by gathering in large groups rather than small ones. 

 

Where would the sentence best fit?

 

 

10. Directions: An introductory sentence for a brief summary of the passage is provided below. Complete the summary by selecting the THREE answer choices that express the most important ideas in the passage. Some sentences do not belong in the summary because they express ideas that are not presented in the passage or are minor ideas in the passage. This question is worth 2 points.  

 

Many hypotheses have been suggested to explain why meerkats take turns acting as sentinels, warning other group members of any threats from predators.

 

 

 

(A) Kin selection is thought to explain sentinel behavior, but this hypothesis does not fully explain how unrelated immigrants can be part of a group.  

 

(B) Even though sentinel behavior can be explained with reciprocal altruism, there is lack of evidence that group members are ever held responsible for not taking their turn to guard. 

 

(C) Guard duty increases the personal safety of every group member, but the increase is at its least for the member who actually stands guard.  

 

(D) The proposed theory that sentinel behavior increases the safety of only family members is contradicted by the sentinel behavior of immigrant group members. 

 

(E) A plausible reason for sentinel behavior may be to allow other meerkats a chance to forage for food in groups rather than as individuals.  

 

(F) Sentinel behavior is most likely the result of self-protection by individuals and only secondarily a means to protect the group.

 

 

 

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