Answer :
I believe it is the second one "more organisms are born than can survive" because natural selection, although it is not solely based on "survival of the fittest" does have to do with an ecosystem that can only maintain a certain amount of organisms, and those that are better conditioned for the ecosystem will survive.
Sorry I cannot be more sure, I had bio quite a while ago.
Sorry I cannot be more sure, I had bio quite a while ago.