Do faster starts increase the probability of evading predators?

1. Nearly all fish evade predation strikes by rapidly accelerating out of the strike path, a behaviour called the fast-start evasion response. The many studies investigating morphological, behavioural and ecological correlates of fast-start performance assume that faster starts increase the probability of evasion. 2. We tested this faster-start hypothesis by measuring the effect of acceleration ability on evasion outcome (success, failure) in Guppies (Poecilia reticulata) evading the strike of a natural predator, the Pike Cichlid (Crenicichla alta). 3. Four parameters affect evasion outcome: two parameters important to the predator-prey interaction but not to the faster-start hypothesis - (1) the time required to reach the prey by the striking predator (measured by the initial distance between predator and prey and strike velocity), (2) the evasion path of the prey relative to the strike path of the predator; and two parameters relevant to the faster-start hypothesis - (1) the ability of the prey to generate rapid tangential acceleration (measured by net distance travelled, maximum velocity, and maximum acceleration), and (2) the ability of the prey to rapidly rotate during the initial stage of the fast start. 4. On average, a one standard deviation increase in fast-start performance increases the odds of surviving a predation strike 2.3-fold. These results support the assumption that faster starts increase the probability of successfully evading a predation strike.