Sib cannibalism can be adaptive for kin

Sib cannibalism seems to be paradoxical behaviour, since it decreases the survival rate of the closest relative juveniles, so the rate of sib cannibalism changes the demography of the cannibal phenotype. In the general kin demographic selection model presented here, the long-term growth rate of a phenotype is determined by a Leslie matrix that depends on the life history strategy, and a uniform density-dependent selection process takes place, keeping the total population size at the level of the carrying capacity. Using this model, where different phenotypes are described by different Leslie matrices, we point out that the phenotype optimizing the phenotypic long-term growth rate will select out any other optimizing phenotype. We find that sib cannibalism is adaptive if the sib cannibal can decrease its developmental time, and the shorter development time can increase the rate of survival from sib cannibal juvenile to adult, and also when sib cannibalism increases fecundity in the adult stage. Cannibalism between the closest relatives can be considered as a mutualistic kin strategy when the benefit of cannibalism is greater than the cost of it.