generis wrote:
Harvester-ant colonies live for fifteen to twenty years, though individual worker ants live only a year. The way a colony behaves changes steadily in a predictable pattern as the colony grows older and larger. For the first few years, the foragers behave quite aggressively, searching out and vigorously defending new food sources, but once a colony has reached a certain size, its foragers become considerably less aggressive.
If the statements above are true, which of the following can most properly be concluded on the basis of them?
A) As a result of pressure from neighbors, some colonies do not grow larger as they become older.
B) Unpredictable changes in a colony's environment can cause changes in the tasks that the colony must perform if it is to continue to survive.
C) The reason a mature colony goes out of existence is that younger, more aggressive colonies successfully outcompete it for food.
D) The pattern of changing behavior that a colony displays does not arise from a change in the behavior of any individual worker ant or group of worker ants.
E) A new colony comes into existence when a group of young, aggressive workers leaves a mature colony and sets up on its own.
CR09740.02
Harvester-ant colonies live for 15-20 yrs
Individual worker ants live only a year.
The way a colony behaves changes steadily in a predictable pattern as the colony grows older and larger.
For the first few years, the foragers behave quite aggressively, searching out and vigorously defending new food sources.
Once a colony has reached a certain size, its foragers become considerably less aggressive.
The colony's age and size determine how the foragers behave. They live for only 1 year so every year, there is a new work force. Their behaviour is dictated by the colony age and size. If the colony is new and small, they are aggressive. If the colony is old and big, they are passive.
The point being made here is clearly that the workers' behaviour does not dictate their actions (whether they are passive or active). It is the colony size that does.
What can we conclude?
A) As a result of pressure from neighbors, some colonies do not grow larger as they become older.
The argument does not talk about pressure from neighbours.
B) Unpredictable changes in a colony's environment can cause changes in the tasks that the colony must perform if it is to continue to survive.
No support in the argument.
C) The reason a mature colony goes out of existence is that younger, more aggressive colonies successfully outcompete it for food.
This is sound reason and seems to make sense as per the argument but the argument does not mention why a mature colony goes out of existence. It just says that in a mature colony, the foragers are not aggressive. But they may still be providing enough. The argument doesn't tell us why a colony has a life of 15-20 yrs. Perhaps it has something to do with lifecycle of an ant - whatever.
D) The pattern of changing behavior that a colony displays does not arise from a change in the behavior of any individual worker ant or group of worker ants.
Correct. The pattern of changing behaviour of a colony is a function of its own size and age, not of the behaviour of any one or group of ants. Ants behave as per the size and age of the colony. Their behaviour does not change. Ants change (new ones come every year).
E) A new colony comes into existence when a group of young, aggressive workers leaves a mature colony and sets up on its own.
We don't know how and when a new colony comes into existence. Nothing mentioned about ants leaving a colony.
Answer (D)
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