Okay, my teacher assigned this homework question, but nothing like this was ever given in our textbook. Suppose that a type of tree tends to speciate over 10 million years and a species of fly tends to speciate over 1 million years. In the event of a mass extinction, which of the following predictions would LIKELY be true?

  • A) It is impossible to determine how many niches or species the trees and flies would lead to over time.
  • B) The trees would fill more niches and create more species than the flies.
  • C) The flies would fill more niches and create more species than the trees.
  • D) They would both lead to the same number of species.

I am stuck between A, B, and D because A would have merit, as speciation period may not always correlate to have many changes occur, B may have merit because it could be showing a Gradual model of speciation, and D may have merit because they might both just end up as the one species described? Any help, not even an answer but guidance would be really great.

  • 3
    $\begingroup$ I appreciate that you have given which answers you think are the best possible and are now asking for help. Homework questions here can be a slippery slope, but I believe you have shown your due diligence and why you need help with it. Welcome to Stack Exchange Biology, by the way! If you have any issues or questions, please visit the help center! $\endgroup$
    – L.B.
    Commented Feb 11, 2019 at 16:38
  • 1
    $\begingroup$ Given that this is a homework question, the answer is C. It is true that there isn't enough information given to answer this question, but there rarely is for homework questions. The point is to keep the number of variables small so that a single best answer can be determined, not to perfectly reflect reality. The only information you are given is the time taken for speciation to occur, which means that you should assume that all other variables don't matter in this case. All other things being equal, the one that speciates faster will fill more niches. $\endgroup$
    – Jeremiah
    Commented Feb 15, 2019 at 19:57

3 Answers 3


The answer is C

Because it explicitly tells you the fly speciates faster than the tree (1my vs 10my). That means after the extinction event, all things being equal, the fly will speciate into more niches/species in the same amount of time. While other outcomes could occur, with the information given C is by far the most likely outcome.

This is no different than a physics question asking you which of two object will reach some arbitrary marker first give two different known velocities.


It's a very strange question and hard to know for sure what they are trying to ask. My thoughts would be that they mean, given the opportunity to speciate following a mass extinction which would be expected to produce the most species after some time. The answer would then be C, that number of fly species > number of tree species because they speciate at a higher rate this would be the "likely" outcome - however, any of the three predictions could occur in reality.

I rule out A becuase it's not a prediction, B would be the expectation if the rate was higher in trees, and D would be the expectation if the rates were the same. As long as you can justify the answer I see no reason for them to complain - part of the issue is the odd question, that's the teacher's/author's fault.


The information in the question, as given, is insufficient to provide any answer about niche filling. If the speciation rates are known, and differ (which is, I assume, given above as average waiting time to speciation), and extinction intensity is assumed equal for both groups ("fly" and "tree"), then "fly" is likely to leave more species, and neither (B) nor (D) can be correct. That leaves (A) and (C). There is no information about the rate of filling niches, so (A) must be correct. Note that this is especially true, if the information I list as assumptions is also not given.


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