On Alternative Reproductive Tactics in Anurans: Dynamic Games with Density and Frequency Dependence

Intense mating competition and mate choice has favored the evolution of alternative mating tactics in many species. We developed a stochastic dynamic game to evaluate the choice among three alternative mating tactics by male anurans: call, satellite, or leave the chorus to forage or hide. The strategies were assumed to differ in mating success (call > satellite forage = hide), predation risk (call > satellite > forage > hide), and energetic expense (call > satellite = hide > forage). Six major predictions were derived. First, in relatively stable environments, males should enter a chorus in a synchronous pulsed pattern, with first-year males primarily choosing to be satellites on older calling males. The pulsed pattern is caused by the relatively high energetic cost of calling and the dependence of female arrival rates on chorus size (which promotes synchronization). In unstable environments, energetic constraints are reduced because favorable conditions are rare, so most males should call on favorable nights. Under all conditions, energy-constrained males should forage. Second, with an accelerating relationship between female arrival rate (measured per calling male) and chorus size, first-year males in a stable environment should drop out of choruses before the end of the breeding season because the payoff to attendance decreases as the population declines; with a decelerating function, first-year males should remain the entire year. In an unstable environment, males should enter a chorus on favorable days, irrespective of the shape of the female arrival function. Third, variation in the form of predation risk with respect to chorus size has little or no effect on mating patterns; however, high mean predation risk should increase the frequency of satellites in the chorus. Fourth, conflicts can occur between old males that are selected to call and young males that are selected to act as satellites. Under some conditions, the only resolution to this conflict is for all males to abandon the chorus. Fifth, if there are differences among first-year males in when they come into breeding condition, the few males that mature early should be satellites. Later in the season, first-year males should tend to call. This prediction is unaffected by density dependence in predation risk, but it does not hold when female arrival rate is density independent. Finally, first-year males should call more when their mating success decreases with an increase in the number of calling older males in comparison with conditions in which mating success is a fixed fraction of the mating success of older males. We show that the properties of a number of anuran species make them amenable to test these predictions.