Unsuccessful Predation and Evolution

The theory of evolution by natural selection requires the recognition of aptations. A given genetic variant can be shown to have an advantage over another with respect to an individual's viability in a given environment if (1) some individuals in the population reproduce after an encounter with the agent of selection for which the variant is believed to be beneficial, and (2) the beneficial variant has a higher frequency among individuals which have survived encounters with the agent than among those which died as a result of the encounter or among those which did not encounter the agent. In the special case of evolution of antipredatory features, unsuccessful predation is a necessary condition. A literature survey of 60 predaceous species reveals that unsuccessful predation is widespread; only 19 of 100 prey species (19%) were attacked in one or more vulnerable size classes with an efficiency (measured after the prey was detected) of 90% or more. The nature and effectiveness of antipredatory defenses can be evaluated by measuring the efficiency with which predators detect, pursue, and subdue prey. The most effective defense of the prey is that used during the phase of predation in which efficiency of the predator is lowest. For prey which are drilled by gastropods, for example, the hypothesis that escape is the primary defense is supported by data on predatory efficiencies during the pursuit and subjugation phases. The incidence of sublethal damage is a conservative estimate of the potential for selection in favor of resistance to subjugation. The literature on sublethal injury in molluscs and butterflies supports the idea that armored species and morphs sustain higher levels of sublethal injury than do their less well-defended counterparts. Comparisons of frequencies of sublethal damage further reveal geographical, ecological, and temporal patterns in the importance of subjugation as a component of selection. These patterns include increases in antipredatory selection from high to low latitudes and altitudes, from fresh to salt water, and from Paleozoic to Recent time, and accord with previous evidence and predictions. Predation is an important cause of evolutionary change. Coevolution between predator and prey may often be indirect, because an increase in predatory efficiency often accompanies enhanced antipredatory defense by the predator and is not brought about by evolution in the prey. The hypothesis that prey have an evolutionary advantage over predators in an "arms race" may be true only in situations where the two parties can potentially kill each other.