If Wisconsin is any guide, Iowa’s public-sector unions are facing a precipitous decline in membership even as their leaders vow to survive the effects of the overhaul of the state’s 43-year-old collective bargaining law.In the five years after Act 10 was approved in Wisconsin, membership in two of the three councils of the American Federation of State, County and Municipal Employees union dropped by 70 percent, according to the Milwaukee Journal Sentinel.