[anamax]

> As food gets more expensive, people will have less children.

Food has to get really expensive before birth rates decline. Survival rates get hit first by lack of food.

> Birth rates are below replacement rates in a lot of countries that keep their population growing mostly by immigration.

The countries that have low birth rates are rich, not poor. To be crude, TV is one of the most effective better birth control devices. (The poor countries with low/shrinking population have man-made disasters.)