Condé Nast Publications Inc. absorbed nearly two decades of losses at the New Yorker. On Monday, it pulled the plug on Portfolio magazine after less than two years.

The closure of the monthly business glossy shows how profoundly the advertising downturn has shifted the paradigm at Condé Nast, a publisher with a reputation for operating less out of concern for profit than the cachet its slate of prestigious titles conferred. The recession has accelerated the erosion of advertising across print media, including...