Jim Bennett asked in the comments of this post:
One of the chief issues here is whether the birthrates of second-and third-generation immigrants from high-birth-rate countries remains high, or whether the immigrants assimilate to local values. Historically, immigrants from high-birth-rate countries have adopted birth rates of their hosts throughout the West, except for religious communities that deliberately isolate themselves from the mainstream. These have included, in the USA and Canada, groups like Old Order Amish, Hutterites, and certain strictly-observant Orthodox Jews. The question then becomes, if the radical Islamists set the tone in segregated enclaves, including enforcing Salafist codes of behavior on women, will this not continue the traditional attitudes about birth rates as well?
This English language page at the German Interior Ministry’s website gives a first hint:
Sex, age and birth rates
In 2003, 3.4 million foreigners (47%) were women and 3.9 million (53%) were men. With an average age of 34, foreigners are younger than native Germans by eight years. In 2003, of the 76,200 children born to foreigners in Germany, 39,355 received foreign citizenship (6% of all births in Germany); the remaining 48% were given German citizenship on the basis of the Nationality Act, in effect since 1 January 2000 . In 1999, the fertility rate of foreign women was 1.8 births, with a downward tendency, compared to 1.4 births for German women.
So even the somewhat more fertile immigrants don’t have a high enough birthrate to replace themselves. As indicated, their birthrates also are declining. According this German website, they quickly converge with the birthrate of the general German population, and soon will have 1.3 children per couple, the same as we have.
Zuwanderer gleichen ihr Reproduktionsverhalten schnell an das der “Einheimschen” an. So haben die in Deutschland lebenden Italiener und Spanier inzwischen noch weniger Kinder als die Deutschen. Die Geburtenrate der Türken Deutschlands nähert sich in schnellem Sinkflug von derzeit 1,7 dem statistischen Durchschnittsniveau der Deutschen von 1,3.
(Availability of the website seems to be sporadic).
There are religious zealots here, but not nearly enough to have an effect on Muslim birthrates, as Jim speculated. The reason why Germans have so few children are the huge economic disincentives – having children is by far the leading cause of poverty. While extended families could help young couples to have more than two children, all their resources would be used up, and the sacrifice is too much for all but the most traditionalist Muslims.
Ulrich Speck mentioned in the comments to the same post that Turkish men often marry wives from Turkey, rather than a Turkish woman who grew up in Germany. While this creates problems for the integration of the children, since their mothers rarely learn proper German, it has little impact on Turkish birthrates. Many Turkish woman who grow up here either remain single, or marry a German man or at least one from some other European country.
As to religious conversions: For every German converting to Islam there are many Muslims who capitulate before our secular society. They give up teaching their children any values, to wit, Muslim girls running around half-naked in warm weather. While some children of such parents will turn to Islamists for values and guidances, hedonism and consumerism are more frequent attitudes
Regardless of ethnicity or religion, having children has to become affordable again, or Germany will gradually become an empty country, rather than an Islamicized one. We also can’t afford to let a single child’s potential go to waste, for we haven’t any to spare. Even if we just wanted to keep our current, already undesirable age structure of the population constant, we would have to let in more than 100 million immigrants over the next decades. This would be neither possible nor even desirable, so we have to make the best of an unenviable situation. Irrational fears of a so-called ‘Eurabia’ would be a distraction and a hindrance towards that goal.