EFFECTS OF SIMPLE ENVIRONMENTAL FEEDBACK ON SOME POPULATION-MODELS

Lovelock used a model of an idealised planet to demonstrate the stabilising effect of feedback on a population of daisies and environmental temperature. The equations he used represented a population model with only two steady states: no daisies present, or a stable population with monotonic damping. This paper investigates whether a similar result is obtained with a less stable population model. It was found that simple feedbacks, mediated by albedo and temperature, or by CO2 and the "greenhouse" effect, did not alter the basic properties of population models but could alter the stability regime within which a certain set of population parameters operated. Models of populations with discrete generations tended to be less stable with feedback while those with continuous growth were more stable. This confirms that Lovelock's result is not highly dependent on the type of population model. Adding environmental feedback to simple population models does not alter the basic properties of the models themselves but leads to a stabilisation of the whole system of environment plus population.