The factor most likely to result in a decrease in the size of a specific population

Famine.

Explanation:

Famine, a shortage of water or food, will often result in a significant population decrease.

explanation:

b,bacteria convert nitrates

into nitrogen gas.

d,plants and animals take in

and use nitrogen compounds.

e,bacteria break down waste    

products and return nitrogen  

to the soil.

a,bacteria convert atmospheric

nitrogen to ammonia.

c,bacteria convert ammonia

to nitrites and nitrates.

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