The costs and benefits of frog chorusing behavior
- Cite this article as:
- Ryan, M.J., Tuttle, M.D. & Taft, L.K. Behav Ecol Sociobiol (1981) 8: 273. doi:10.1007/BF00299526
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A number of predators, including a bat (Trachops cirrhosus), a frog (Leptodactylus pentadactylus), an opossum (Philander opossum), and a crab (Potamocarcinus richmondi), prey on the neotropical frog Physalaemus pustulosus, which calls in choruses on Barro Colorado Island, Panama.
Predation rate (no. of frogs eaten/h of observation) and predation risk to individuals (predation rate/chorus size) were determined for choruses of various sizes. There was no correlation between chorus size and predation rate, but there was a significant negative correlation between chorus size and predation risk.
There was a significant correlation between the number of females present and chorus size (i.e., number of males). A second order regression indicates that the proportion of females to males, the operational sex ratio, tends to increase with chorus size; thus, males have a higher probability of mating in larger choruses.
We suggest that the benefits of lower predation risk and higher mating probabilities associated with larger choruses were responsible for the evolution of communal sexual display in Physalaemus pustulosus.
A cost-benefit model predicts that the size of males that join choruses is influenced by the asymmetric benefits related to male size and the behavior of other males in the population.