Population dynamics of egg cannibalism when cannibals gain life history benefits: A life table approach using Coccinellidae as a model system

We used life tables to model rates of population growth when egg cannibalism by specific life stages increases developmental rate and/or fecundity, using aphidophagous coccinellids as a model system. Sibling egg cannibalism was beneficial for population growth; a modest (10%) increase in developmental rate or fecundity was sufficient to favour cannibal over non‐cannibal populations, provided the rate of cannibalism remained low. The highest rates of population growth occurred when cannibals received both developmental and fecundity benefits, the former being more beneficial than the latter. As cannibals increased in number, the costs to population growth rate eventually outweighed the individual life history benefits, such that the proportion of cannibal individuals (or cannibalism rate) was limited in a frequency‐dependent manner. Simulations of cannibalism by later stages (fourth instar larvae or adults) often led to cannibals comprising more than 50% of the population, depending on the magnitude of individual benefits, as the costs of cannibalism (mortality) were shared by both cannibals and non‐cannibals, in contrast to sibling egg cannibalism, in which cannibals alone bore the costs. We conclude that cannibalism can evolve in the absence of resource limitation, as cannibals can easily invade non‐cannibal populations when they gain life history benefits, although higher levels of cannibalism become self‐limiting by the constraints they impose on population growth rate.