Falling into a niche: Institutional equilibrium between plurality and proportional representation for large political parties

Scholars of electoral systems (e.g,, Duverger 1954; Rae 1967) argue that a combination of electoral system and district magnitude provides the strategic incentives for political party competition. All electoral systems reward large parries with a disproportional seat bonus, with this bonus being more pronounced in plurality/majority systems. Thus, large parties invariably wish to compete in majoritarian systems while smaller parties seek a proportional system of seat allocation. This study shows that an institutional "niche" develops in some party systems where the second-largest party prefers the current electoral system over either a more proportional or more majoritarian system. Specifically I illustrate how parries in Irish, Tasmanian, Australian House, and Australian Senate elections occupy such an equilibrium. Vote transfers create a seal bonus that does not exist in either more proportional or more majoritarian systems (e.g., the Single Non-Transferable Vote).