When m-selection?

Caswell and Hastings (1980) introduced an explicit model for the relative merits, in terms of the growth rate λ, of developmental shifts vs. fecundity increases. Some aspects of their model are clarified by concentrating on the (fitness>1) half-plane rather than on the (accelerated reproduction) half-plane. There is no strict equivalence between Caswell and Hastings' key parameter \({\lambda \mathord{\left/ {\vphantom {\lambda {\tilde P}}} \right. \kern-0em} {\tilde P}}\) and the dynamic behaviour of the population which is governed by λ. Thus in some stationary/declining populations time shifts of reproduction (forward or backward, according to the value of \({\lambda \mathord{\left/ {\vphantom {\lambda {\tilde P}}} \right. \kern-0em} {\tilde P}}\) ) are just as effective in promoting a high λ as they are in growing populations; therefore selection for higher m _x may, but need not, prevail in stationary/declining populations.