Logical Reasoning

PT134 · S1 · Q8 According to the

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According to the "bottom-up" theory of how ecosystems are structured, the availability of edible plants is what primarily determines an ecosystem's characteristics since it determines how many herbivores the ecosystem can support, which in turn determines how many predators it can support.

Theory's Conclusion

The availability of edible plants is what primarily determines an ecosystem’s characteristics. (a corollary belief: reducing number of predators wouldn't have much impact on the rest of the ecosystem)

Theory's Evidence (since)

The availability of edible plants in an ecosystem is what determines how many herbivores the ecosystem can support.

The number of herbivores determines how many predators an ecosystem can support.

Goal

Since the question stem just asks us to pick an answer that goes against the bottom-up theory, it could go against any part of what we just read.

- It could point to something BESIDES availability of edible plants that is the primary determinant of an ecosystem's characteristics. (maybe the availability of fresh water is the primary determinant)

- It could dispute the idea that availability of edible plants determines how many herbivores the system can support (the answer could show two ecosystems that have similar edible plants but differ greatly in terms of how many herbivores they support).

- It could dispute the idea that reducing the number of predators has little impact on the ecosystem (the answer could show us some comparison that makes it look like actually reducing number of predators DOES make a big difference)

Which one of the following, if true, would provide evidence against the bottom-up theory?

In an effort to build
Opposite (if anything)
This seemingly supports the bottom-up theory because it shows that the number of edible plants can impact whether monkeys can survive in that ecosystem.
1% picked this
Correct
After hunting virtually eliminated predators
Why this is right
This provides a counterexample to the theory and shows that a reduction in the number of predators had a significant impact on the rest of the ecosystem. Hunters reduced predator populations and this had huge impact on the rest of the ecosystem -- there ended up being ten times as many herbivores and way fewer plants. The causal chain in this answer is very Top-Down fewer predators >> more herbivores >> fewer plants
Skill tested: Weaken · how this choice captures the argument's function is the move to repeat next time.
85% picked this
After many of the trees
Opposite (if anything)
Just like (A), this shows how the availability of plants impacts things higher on the food chain. fewer trees >> fewer ants >> fewer anteaters This supports the bottom-up theory because it shows that the number of plants can impact the rest of the ecosystem.
4% picked this
After a new species of
No Impact
This essentially describes a neutral change, where the availability of one plant was supplanted by a somewhat equivalent plant. It doesn't really help us assess anything, because the availability of edible plants didn't change quantitatively (it's just that one type of edible fern was replaced by another), and the ecosystem didn't really change either.
5% picked this
Plants that are a dietary
Unclear Impact
The bottom-up theory would probably predict that as edible plants that pigs like flourish, that should lead to more pigs. This answer gives off the vibes that it hasn't led to more pigs, but it kinda HAS! The pigs have been extensively hunted, which should have brought their population numbers way down. So why are the pig numbers stable? Probably because as the effect of extensive hunting was reducing their population, the effect of flourishing edible plants was increasing their population. These offsetting effects basically canceled each other out. But if anything we might consider this strengthening the bottom-up theory because it seems to suggest that flourishing plants helped boost the number of pigs.
5% picked this

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