DIMENSIONLESS INVARIANTS FROM FORAGING THEORY MARGINAL VALUE THEOREM

Copula duration (t) decreases, and proportional rate of sperm transfer (c) increases, with larger male body size in dung flies, so their dim ensionless product (c . t) is approximately constant (approximate to 2 .2). The most recent copulating male fertilizes about 89% of the eggs laid (= 1 - e(-c . t) = 1 e(-2 . 2)), independent of his body size. Th e conditions under which natural selection favors this phenotypic inva riance are studied with fitness optimization models, The dimensionless rules for optimal patch residence times are then generalized to cover phenotypic variation in other foraging cases.