For the past five years, Ernie DiGiacomo has been able to count on parents to guarantee the $1,500 to $2,500 rents he charges for the 15 apartments he owns in Williamsburg, Brooklyn. When he called renters who had missed payments, he often heard, “My parents will send you a check.”

But in the past six months, the parents are pulling back financial help, he said, and as a result, he has watched more renters move out.

“Most of them are moving back with parents,” Mr. DiGiacomo said.

Luis Illades, an owner of the Urban Rustic Market and Cafe on North 12th Street, said he had seen a steady number of applicants, in their late 20s, who had never held paid jobs: They were interns at a modeling agency, for example, or worked at a college radio station. In some cases, applicants have stormed out of the market after hearing the job requirements.

“They say, ‘You want me to work eight hours?’ ” Mr. Illades said. “There is a bubble bursting.”

Famed for its concentration of heavily subsidized 20-something residents  also nicknamed trust-funders or trustafarians  Williamsburg is showing signs of trouble. Parents whose money helped fuel one of the city’s most radical gentrifications in recent years have stopped buying their children new luxury condos, subsidizing rents and providing cash to spend at Bedford Avenue’s boutiques and coffee houses.