Variation and Consistency in Spatial Distribution as Measured by Taylor's Power Law

Abstract

To investigate the spatial isotropy of Taylor's power law, data of the aerial population densities of western flower thrips, Frankliniella occidentalis (Pergande), were compared at 6 greenhouses in northeastern Ohio. The distributions were the smne in all 6 houses despite differences in crop (host plant) and in thrips population growth and development. Comparison with data from the literature on F. occidentalis distributions obtained in houses with horticultural crops using closely similar sampling methods revealed a consistency of distribution over a range of plant architectures. The consistency of power law results means that the same sampling program may be used for F. occidentalis in a variety of greenhouse crops. In contrast, samples taken within the canopy of a cucumber crop resulted in Taylor's power laws significantly different from those obtained with samples taken above the canopy. Taylor's power law appears to remain constant provided the same statistical population is being sampled. Sampling the same reproductive population under different conditions (e.g., stage, phenology, or habitat) can result in different power law estimates, as reported by some authors. Possible reasons for power law differences and the significance of power law constancy also are discussed. Tables for optimum sample size are given for sampling F. occidentalis in greenhouse crops using industry standard yellow sticky cards. In addition, it is shown how the number of samples required for a fixed level of precision can be manipulated by varying the sampling efficiency or size of sampler.