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Can anyone please help with this bio ap question?

Picture of Iris Xu
Can anyone please help with this bio ap question?
by Iris Xu - Sunday, May 9, 2021, 12:58 PM

which of the following is a biotic factor that could affect the growth rate of a population?
a) volcanic eruption
b) glacier melting
c) destruction of ozone layer
d) sudden reduction in animal food source

The answer i chose was incorrect, but i don't understand why.  What would you pick and why?

Picture of Charles Zhang
Re: Can anyone please help with this bio ap question?
by Charles Zhang - Monday, May 10, 2021, 2:50 PM

Let's see here...

a. Unless you're a plant, you shouldn't be very worried about volcanic eruptions.

b. Glacier melting = rise in sea = animals/people move away from the coast.  Most likely, nothing dies, except a few weeds in the sand/rocks near the sea.

c. Albeit being somewhat scary, I wouldn't sweat this.  The suns rays are deadly, yes, but in this context, this isn't what you're looking for.

d. This, I think, is the correct answer.  A sudden reduction in the said animal's food supply would lead to a decline in the population.  Then when the said animal's population declines, the food supply of said animal would increase, since there would be less animals eating it, leading to a sort of up-down pattern.  (See

But, then again, I'm just spitballing here.  This is purely just intuition, my answer is probably wrong, but hey, you asked us, and I'm just answering


Picture of John Lensmire
Re: Can anyone please help with this bio ap question?
by John Lensmire - Tuesday, May 11, 2021, 3:44 PM

Thanks Charles for sharing your thoughts as well!

I agree with the answer of D, although I want to highlight the key phrase of "biotic factor" that I also think is important and can make things a little easier.

Factors that may limit a population are often split into "biotic" or "abiotic" factors. Biotic ones are the ones that actually depend on living things, such as food supplies, other predators, etc. Abiotic factors are other non-living factors or chemical factors. Thus, while you could make an argument that any of the factors could have an effect on the growth rate, A, B, and C would probably be considered abiotic factors.

Iris, hope this helps. If needed I can try to expand some more or find some other explanations as well!