I think that is a contradictory question. I think it IS the law of nature. How/why else would it be occurring the way it is? No one/nothing is making these does abandon their fawns (at the rate they are)but themselves......via some internal (natural?) mechanism. The fact that many of them aren't being bred is additional proof that she's damned good at taking care of herself (Ma nature).
But having it get that far, and reach that levelis something NOT caused by nature. Man's influence and impact created an "artificial" situation that never would have existed under "natural" conditions.