Which one of the following, if true, most clearly weakens the rate–of–speciation hypothesis as it is described in the...

Jay-Etter on January 31, 2022

Hi,
this could be our analysis of the passage:
1) introduce a phenomenon (more species in the tropics - middle latitudes).
2) propose three hypotheses which they end up rejecting (time theory, species-energy hypothesis, climatic stability)
3) introduce and defend a fourth hypothesis, the rate-of-speciation hypothesis.

This question is talking about the fourth hypothesis, the one that the author likes. This hypothesis says "if speciation rates become higher toward the tropics, and are not negated by extinction rates, then the latitudinal gradient would result". The way this explains the latitudinal gradient is because the extinction rate of subgroups that would diverge into a new species is higher in the arctic. So what would weaken this hypothesis? Something that shows the rate of subgroup extinction in the tropics is not lower than that in the arctic.

A) This would strengthen the hypothesis by saying subgroups in the tropics actually diverge into different species.
B) Also a potential strengthen by saying many species can coexist in the tropics (so the extinction rate wouldn't be that high).
C) It wouldn't hurt the rate-of-speciation hypothesis just to add support to another hypothesis (this answer would support the species-energy hypothesis).
D) This one is tempting. However, it's not actually engaging the hypothesis because it's not saying anything about mechanisms of speciation, it's just saying "oh there's actually more in the arctic than we thought". But that doesn't mean this theory is wrong for why there are overall more species in the tropics.
E) This is good. If isolated subgroups go extinct in tropical areas, then they wouldn't speciate and then the theory couldn't explain why there are more species in tropical areas!

Hope this helps, feel free to follow up!

jackvassau on September 4, 2023

Hello, are there video or written explanations of the passages? These are mentioned in the instructional videos, but I do not see an option for them.