Callers and satellites: chorus behaviour in anurans as a stochastic dynamic game

Abstract

Males often compete for mates using alternative tactics whose relative success could be simultaneously influenced by four factors: subsequent behaviour, physiological state, the frequency of expression of alternative tactics and the density of competing males. Here the payoffs to two alternative male mating tactics (call and satellite) were examined in anurans using a stochastic dynamic game. The basic model considers an iteroparous species with a prolonged breeding season and fairly low energetic costs and predation risks. The model assumes that female chorus attendance is affected by weather, time of year and male chorusing intensity. Results show that interactions between energetic costs of calling, density-dependent predation risk and female arrival rates, and frequency-dependent mating success produce distinct temporal waves of male chorusing despite continuously favourable environmental conditions. Relative to second-year males, first-year males attended choruses less often and were more likely to become satellites. When the energetic costs of calling were increased, waves became shorter and less frequent, and some older calling males switched to satellite behaviour. Satellites were less common when breeding season length was constrained by extrinsic factors such as seasonal weather patterns. Extrinsic constraints may also affect system stability: if female arrival rates are independent of male chorusing intensity, an evolutionarily stable strategy occurs only if the breeding season is short. Even without extrinsic constraints, the breeding season may be short if predation rates on adults are sufficiently high, or if satellites intercept a large fraction of incoming females. Thus, the ‘explosive’ breeding systems observed in many anuran species could result from either biotic or abiotic causes.