Population Dynamics of Poikilotherm and Homeotherm Vertebrates: Effects of Food Shortage

We have investigated how the population dynamics of two types of vertebrates is influenced by food shortage. One type consists of animals which show indeterminate growth rate (cut the coat to the cloth), e.g. fish. The other type includes animals which show a determinate type of growth rate (require a minimum daily food supply to survive), e.g. mammals and birds. To this end we have developed a model which assumes that animal biomass is regulated by food biomass alone (i.e. no predation), while food biomass follows self-regulating dynamics. The model predicts stable biomass for the first type of animals and unstable, cyclic biomass for the other. The results help to explain why fish in a pond often develop a stable population of numerous, small individuals, while e.g. hares or moose on an island, shielded from predation, develop a fluctuating population.