Affordable egg mortality: constraining copepod egg mortality with life history traits

The maximum egg mortality that a population can afford if it is not to wane, here labelled the affordable egg mortality, can be estimated from knowledge of life history traits, i.e. fecundity, development time, egg hatching time and post-egg mortality. Examination of changes in the affordable egg mortality with variations in the life history traits yields two main conclusions: when development time is short, the affordable egg mortality, is maximized by reducing the egg hatching time, instead of by maximizing fecundity. In contrast, when development time is long, or when post-egg mortality is high, the affordable egg mortality is maximized by a combination of low egg hatching time and very, high fecundity, or by increasing the egg hatching time. For a growing population, the realized egg mortality should always be less than the affordable mortality. This condition can be exploited to check the validity of measured mortality, coefficients, and is illustrated with two examples from published field studies on marine copepods. These examples reveal that for populations in temperate environments that typically, display growth in the winter and spring months, high egg losses (much greater than 1 day (1)) cannot be sustained unless recruits are supplied from outside the population.