The other day in class, our AP Biology teacher presented us with the following graph and asked us to determine which of the following interspecific relationships it represents:
She explained to us that since there is not enough information in the graph to explain why species A suddenly drops off after time "x" and species B suddenly rises after time "x", the best answer out of the choices is (A) commensalism.
But to me, that seems to be a faulty line of thinking. After all, my teacher arrived at that answer only under the assumption that the graph/question itself is good to begin with. I tried finding graphs of commensalism using Google Images, and I actually found the original source of the graph that our teacher presented us.
Now, the question on Regentsprep actually gives us a point of reference and states that we are considering two herbivores in a grassland environment, so in my opinion it's reasonable to conclude that the relationship between species A and B is competition.
The problem is that my teacher never gave us a frame of reference: she just told us to identify the relationship in this graph without any "backstory". So what are your thoughts: is it possible to conclude that "A" is the best answer choice if we are not given any information aside from the graph?