"which term is the most closely associated with the changes in relative population size shown in graph c?
(1)mutation
(2)artificial selection
(3)genetic engineering
(4)competition"

According to the graph represented above, it does seem to me that the term which  is the most closely associated with the changes in relative population size is 4 - competition. The reason why I choose this option is that there is a couple of population lines which go in totally different ways creating the contrast, as one of the line goes upwards and other one goes down - competition does make sense.
Hope you will agree with me.

This is a time line from 685 to 978