【4月16日阅读】

belinda_cao

Biologists have advanced two theories to explain why schooling of fish occurs in so many fish species. Because schooling is particularly wide spread among species of small fish, both theories assume that schooling offers the advantage of some protection from predators.　　Proponents of theory A dispute the assumption that a school of thousands of fish is highly visible. Experiments have shown that any fish can be seen, even in very clear water, only within a sphere of 200 meters in diameter. When fish are in a compact group, the sphere of visibility overlap. Thus, the chance of a predator finding the school is only slightly greater than the chance of the predator finding a single fish swimming alone. Schooling is advantageous to the individual fish because a predator's chance of finding any particular fish swimming in the school is much smaller than its chance of finding at least one of the same group of fish if the fish were dispersed throughout an area.
　　However, critics of theory A point out that some fish form schools even in areas where predators are abundant and thus little possibility foexcaping detection exists. They argue that the school continues to be of value to its members even after detection. They advocate theory B, the "confusion effect," which can be explained in two different ways.
　　Sometimes, proponents argue, predators simply cannot decide which fish to attack. This indecision supposedly results from a predator's preference for striking prey that is distinct from the rest of the school in appearance. In many schools the fish are almost indentical in appearance, making it difficult for a predator to select one. The second explanation for the "confusion effect" has to do with the sensory confusion caused by a large number of prey moving around the predator. Even if the predator makes the decision to attack a particular fish, the movement of other prey in the school can be distracting. The predator's difficulty can be compared to that of a tennis player trying to hit a tennis ball when two are approaching simultaneously.

1. According to the passage, theory B states that which of the following is a factor that enables a schooling fish to escape predators?
　　A The tendency of fish to form compact groups
　　B The movement of other fish within the school
　　C The inability of predators to detect schools
　　D The ability of fish to hide behind one another in a school
　　E The great speed with which a school can disperse

2. According to the passage, both theory A and theory B have been developed to explain how
　　A fish hide from predators by forming schools
　　B forming schools functions to protect fish from predators
　　C schooling among fish differs from other protective behaviors
　　D small fish are able to make rapid decisions
　　E small fish are able to survive in an environment densely populated by large predators

3. According to one explanation of the "confusion effect", a fish that swims in a school will have greater advantages for survival if it
　　A tends to be visible for no more than 200 meters
　　B stays near either the front or the rear of a school
　　C is part of a small school rather than a large school
　　D is very similar in appearance to the other fish in the school
　　E is medium-sized

4. The author is primarily concerned with
　　A discussing different theories
　　B analyzing different techniques
　　C defending two hypotheses
　　D defending two hypotheses
　　E revealing new evidence