What type of Interspecific relationship does this graph depict?
Competition makes the most sense, IMO. 

For every other type of relationship, A and B should be dependent and roughly proportional: If parasites kill their host, they die in proportion. If predators eat all their prey, they drop in numbers due to food scarcity until food repopulates, the graph would almost look like a double helix. Mutual/commensals also share a dependent and proportional graph. The inverse proportionality of the sample chart, to me, gives away competition: one organism is flat out winning against another through some method.