Cannibalism in Natural Populations

Cannibalism, defined as intraspecific predation, is a behavioral trait found in a wide variety of animals, although most references to this behavior are anecdotal or based on casual laboratory observations, The role of cannibalism in the dynamics of natural populations has been largely neglected; the most elegant and detailed analy­ ses of the population consequences of cannibalism are still provided by laboratory studies of flour beetles (Tribolium) that describe the process, examine its interac­ tions with other population processes, and attempt to derive generalities about its effects (60, 78, 88), Therefore, some authors have suggested that cannibalism is an artifact of laboratory systems (20, p, 324) or that it occurs only in cases of severe stress, especially when alternatives, such as dispersal, are not possible (I05), My purpose in this review is to show that cannibalism is a normal phenomenon in many natural populations, to evaluate its possible roles in influencing demo­ graphic structure and population processes, and to suggest conditions for, and constraints on, its occurrence, Cannibalism may be an interaction that reduces population size before acute resource shortage causes severe physiological stress, and in this sense its effects may be analogous to those of spacing behavior or dominance hierarchies in some social animals (104), I also discuss cannibalism as a limiting case of predator-prey interactions among potential competitors, This review is based mainly on field experiments and direct estimates of rates of cannibalism, but I use papers describing laboratory experiments to supplement the discussion of behavioral triggers and genetic components and to fill gaps in the field evidence, I have excluded numerous references with only casual mention of canni­ balistic events,