From the inverse density-area relationship to the minimum patch size of a host-parasitoid system

The minimum amount of suitable habitat (MASH) is an important concept in conservation biological control. Two methods for estimating the MASH have been proposed by McCoy and Mushinsky based on an inverse density–area relationship. Using data of the population densities of aphid host–parasitoid–hyperparasitoid collected from wheat fields of different habitat sizes, we argued that the inverse density–area relationship may be an artifact. Significant correlations between population densities and patch sizes from all three trophic levels were found once the population density had been log-transformed. We could not obtain the same results if the population density had not been log-transformed. We estimated that the MASH for the aphid M. avena, S. graminum, A. avenae, A. gifuensis, P. aphidis, and Alloxysta sp. were 246, 246, 479, 495, 949, and 835 m2 according to the methods of McCoy and Mushinsky. The scale-dependence and the systematic spatial variations of the host–parasitoid interaction suggests that we can achieve an optimal effect of biological control by manipulating the habitat patch sizes, although not based on the inverse density–area relationship.We are grateful to R. Zhang and Y.Z. Yu for suggestions and the critical comments, to D.W. Huang for helps in identifying the aphid parasitoids, and to D.M. Mager and B. Laniewski for English editing. The research was support by the National Natural Science Foundation of China (30760045 and 30860164) and the NRF Blue Skies Programme