QUESTION TEXT: According to the “bottom-up” theory of how…
QUESTION TYPE: Weaken
CONCLUSION: Removing predators won’t hurt an ecosystem.
REASONING: No evidence is given for the conclusion.
ANALYSIS: The theory predicts that plants are most important. More plants leads to more herbivores. Predators eat herbivores, so their numbers will increase too.
This is true, but it’s not the end of the story. Nature is a system, and effects go both ways. Most ecologists know that if you remove predators, herbivores will run wild and reproduce like mad. Then they eat all the plants, and die. The theory ignores this possibility.
The theory already predicts things will go wrong if you remove plants or herbivores. The right answer has to show a problem that happens because we removed predators.
- The theory would have predicted this. It says that plants are the most important thing.
- CORRECT. This sounds like a problem, and it was caused by removing predators. It seems that predators do play an important role in the ecosystem: they keep herbivores in check.
- This is what the theory would predict. Plants are the most important thing, and removing them destroyed the ecosystem.
- This is consistent with the theory. Plants feed herbivores. So if herbivores can eat the new plant, there’s no problem.
- The theory says that the number of plants determines how many herbivores can survive. This implies that it will be hard to eliminate a herbivore by hunting, as long as there are plenty of plants to eat. If you cut the herbivore population in half by hunting, each herbivore will have more plants to eat and they’ll reproduce more frequently.
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