Optimal Allocation of Parental Investment

Abstract

Optimal investment decisions are evaluated for parents which allocate resources equally among offspring. Optimal investment predicts that: 1) Brood size should be positively correlated with total parental investment. 2) Brood size should decline with increases in maximum juvenile survival. 3) Brood size should increase as the minimum investment in offspring declines. 4) Brood size should increase with increases in the rate of change of juvenile survival with parental investment. Total parental investment and juvenile survival should vary with environmental conditions. Optimum brood size should often be higher in good than in poor periods, but may be just the opposite in good and poor habitats. Optimal investment may frequently be achieved by differential allocation of resources among offspring. Sexual investment theory is a subset of optimal investment theory. 5) The degree of preferential partitioning of investment should depend upon the phenotypic variability of offspring and the length of parental care. 6) Investment-induced changes in phenotypic proportions (e.g., sex ratio) depend upon brood size. Optimal investment differs from other life history models in its assumption that brood size is one of a series of mechanisms operating to optimize parental investment. 7) Reproductive costs should not generally increase with increased brood size.