Resistance and tolerance in animal enemy–victim coevolution

Victim defence against enemies can be divided into resistance (minimizing successful enemy attacks) and tolerance (minimizing the fitness impact of enemy attacks). Although resistance has a negative effect on enemy fitness, tolerance, by this definition, does not necessarily; the relative importance of resistance and tolerance within a population might therefore affect enemy–victim coevolution. Resistance and tolerance have been distinguished in studies of plant defence, whereas most studies of antagonistic interactions in animals have focused on resistance, neglecting tolerance. We suggest that tolerance is also an important means of defence in animal victim–enemy interactions such as brood parasitism, mating interactions and territoriality. We discuss the potential coevolutionary consequences of tolerance variation in these animal enemy–victim interactions.