The issue isn't whether the aforementioned birth rates are dropping. They tend to when populations become more middle-class, though some groups take advantage of the welfare state to actually up their repro rate. What matters, though, is THE POPULATION ALREADY BORN AND IN PLACE vis-a-vis "competing" populations. That isn't speculation, it can be projected--barring, of course, The Unforeseen. Without assimilation, without changes in value, the problem is real and significant.