Public choice theorists say that as the number of potential voters in an election falls, this causes a perceived voting that affects the percentage turnout of voters.

rise in the benefit                                                    

Explanation:

            Gordon Tullock and James Buchanan conceptualized and developed the theory called the  "public choice theory" which states the importance of how people decisions are made with respect to the political realm.  It mainly involves the interaction and coordination of the politicians, public voting, political action committees and the bureaucracy.

            It is seen that when potential voter do not vote in an election or their number falls, it benefits the voting ratio and rises the percentage turnout of the voters.

Thus, the answer is -- "rise in the benefit".