Operational sex ratios in Bufo rangeri: A test of the active–inactive model

Abstract

The active–inactive model predicts temporal variation in the operational sex ratio (OSR) throughout a breeding season, as a function of each male’s optimal strategy for finding mates. I tested the model using data for the raucous toad, Bufo rangeri, collected nightly over three breeding seasons. The numbers of active males and fertilizable females were correlated in two of the three breeding seasons. The OSR, defined as the average ratio of sexually active males to fertilizable females,  decreased throughout each season, except for the first, when it rose to a peak before decreasing. The OSR fluctuated towards the end of the season in two of the three seasons, and rose again at the end in only one. Although the equal-performance assumption was violated, the temporal pattern of the OSR in this species complied largely with that predicted by the active–inactive model.  Reasons for deviations from the model’s predictions are discussed. Despite the lack of data on mortality rates, this study  represents the most comprehensive test of the model yet, as tests on other species have been based on data collected  intermittently, as opposed to nightly, over only two breeding seasons.

Key words: raucous toad, reproduction.