Fiction perhaps, but not science. Time travel stories—especially those invoking paradoxes—are fantasy. "Tribbles" on the other hand is highly "realistic." There have been uncounted instances where Mankind has had to deal with the explosive and unexpected results of tampering with the balance of an ecosystem.
I said science fiction
not science. No where does it say science fiction has to be realistically scientific. If that was the case than Star Trek is most decidedly not a science fiction show.