Population dynamics of newly introduced species: Population growth in some introduced insects in New Zealand
Whereas experimental patterns of population growth can be satisfactorily determined in the laboratory, their application under field conditions is not easy, although it has been done to a limited extent, e.g., Davidson in Australia on thrips in roses. This contribution is a rather general account of the progress of three newly- introduced species with observations on some factors considered to have influenced population growth. In general the population growth curve of these introductions is shown in the following figure.
Section A of the curve is the period of establishment after which, under favourable environ mental conditions, there is a period of rapid increase B, until numbers reach near stability at C, and thereafter attain an equilibrium in which there are numerous fluctuations. The pattern of the graph covered by periods A, Band C forms a sigmoid curve. Features of the growth patterns of the following three insects will be considered in relation to the curve.