[ QUOTE ]
Can you explain this idea more please?
[/ QUOTE ]
Wealthy countries are already shrinking if you ignore immigration/emigration. Approximately 2.1 children are required per family to maintain a steady-sized human population in a first-world environment. Several wealthy countries (notably most of Europe, Japan, Canada, the U.S. and Australia) are already failing to reach this number meaning the countries with tighter immigration policies (Japan) are likely to experience population declines in the near future.
Obligatory wikipedia reference
A
United Nations report expects world population to begin to decrease naturally after 2075 after reaching a maximum of fewer than 10B people. (Although to be fair that is the median of their assumptions, on the high end population would continue to grow to 36B by 2300).