Effects of competitor-to-resource ratio and predation on competition in the guppy (#689)
Typically, males exhibit higher rates of intrasexual aggression and courtship behaviour when competing for mates than do females. The best predictor of these rates is the competitor-to-resource ratio (CRR; number of competitors/number of ready-to-mate members of the opposite sex); mating competition typically increases as members of the opposite sex become rarer. Moreover, in high predation populations, males often decrease their rate of mating competition due to the risks of predation and the costs of anti-predator behaviour. Under laboratory conditions, we explored the combined effects of CRR (i.e. 0.2, 0.5, 1, 2, 5) and chronic predation (Upper Aripo population: low risk, Lower Aripo population: high risk) on mating competition in male and female wild-caught Trinidadian guppies (Poecilia reticulata). Surprisingly, females were just as aggressive as males when competing for mates. Regarding mating tactics, the rates of both courtship and forced mating per male increased as CRR became female-biased whereas courtship propensity (courtship/male corrected for female availability) was not affected by CRR. Finally, guppies from a high chronic predation population showed significantly lower aggression rates than those from a low predation population, but male mating tactics did not differ. These results are probably the consequence of trade-offs between anti-predator behaviour, and mating competition.