A Synoptic Population Model

(1) A synoptic model of population dynamics, incorporating population density, population growth and habitat stability, is described. Habitat stability is considered related to the r-K selection continuum. (2) The model is arrived at by variation of the natality curve, natural enemy action and intraspecific competition as expressed in nine parameters. (3) The r-strategist's `boom and bust' dynamics are related to the ephemeral nature of its habitat and the form of its population growth curve is strongly influenced by the finite nett rate of increase (lambda). (4) The K-strategist is characterized by the high survival rate of the reproductives and the low recruitment into this age class. Some K-strategists may produce many young; strategies of `masting' and `escape in space and time' are identified. In the model the form of the K-strategist's population growth curve is influenced by the co-operation component of the finite nett rate of increase. The population is often in the region of the upper equilibrium point, determined by competition. (5) The central portion of the model contains the natural enemy ravine, where predator's effects are most significant. Where the ravine dips below the zero growth contour there is a lower predator maintained equilibrium point and a `release point R' beyond which the population becomes epidemic. Endemic and epidemic regions are clearly recognized. The influence of the different parameters of the functional and numerical responses of natural enemies on the width of the ravine is shown. (6) At the r-end of the ravine the numerical response is limited; the significant predators, whose equilibrium is at relatively low densities, are often polyphagous and large relative to their prey. (7) At the K-end of the ravine the saturation point of the numerical response and handling time are higher. The equilibrium point is at relatively higher densities than at the r-end, i.e. close to the carrying capacity (K), so narrowing the `epidemic ridge'. (8) The model is used to describe field-data on endemic and epidemic populations of aphids and eucalyptus psyllids and to correlate experience in biological control situations. (9) Stochastic simulations of populations characteristic of different regions of the model have demonstrated the influence of the width of the ravine, the extent of compensation in the density dependent moderator of the competition effect and the level of stochastic variation (`noise') on pattern of population fluctuat