Discussion: The Kermack-McKendrick epidemic threshold theorem

Abstract

Modeling the growth of animals as parts of ecosystems often presumes the existence of an asymptotic weight which, when reached by the individual, stops its further growth. We show that the asymptotic weight is influenced by environmental conditions, and that growth is limited because of a trade-off of foraging costs and gain of feeding. We show that the so-called asymptotic mass is a comprehensive value, which also contains an environmental parameter. We develop our model for organisms of neutral buoyancy in an aquatic environment; for terrestrial and aerial animals it has limited validity only. We discuss examples and derive a critical value for resource availability in a habitat, which informs us whether foraging in that habitat is worthwhile or not. 1.