For the first election of members of the council of a municipal corporation after the adoption of the federal plan under sections 705.71 to 705.86, inclusive, of the Revised Code, in any municipal corporation having ten thousand inhabitants or more, the municipal corporation shall be divided into wards by the legislative authority existing under the plan of government to be superseded. Immediately after the proclamation by the secretary of state as to the population of the municipal corporations, as determined by the federal census, the council may redivide the municipal corporation into wards upon the basis of its population, which shall be as nearly equal in population as possible and composed of contiguous and compact territory, bounded by natural boundaries or street lines. Any member of the council, elected from wards, who, at the time of his election was a resident of the ward which he represents, shall forfeit his office if he removes from such ward, and the council shall fill the vacancy for the unexpired term.