From great Gerald Seib WSJ column.
Islam, hugely fertile throughout history (a sign of high infant/child mortality), starts losing fertility big-time once globalization kicks in.
You know my Core-Gap map. You're looking at the Gap highlighted there and numbers are dropping rapidly as globalization creeps in.
Discard the Nordic and US references. Those are tiny numbers in absolute terms.
Point is, Islam responds to global connectivity/globalization/ modernity like everybody else: fertility drops.
Remember that when somebody tells you that Muslims are going to take over the world because of their incredible fertility.