Biodiversity evaluation in agricultural landscapes: above-ground insects

In agriculture, sustainability can be linked to ecological resilience. In view of present or imminent environmental changes in agricultural landscapes, the diversity of species and genotypes, particularly of potential beneficials and alternative prey, may become of increasing importance. However, the available methods and empirical data concerning species diversity of above-ground insects in agricultural landscapes do not yet allow comprehensive evaluation. Standardized inventory methods must be used more rigorously and over longer time periods to detect significant differences in space and in time. Indicator groups for biodiversity estimates must be defined. Methods for optimizing the reliability and comparability of faunistic inventories are proposed, including rarefaction for reference functions and estimation of species numbers per unit area. Recommendations for optimum sampling periods and average empirical numbers for species diversity and abundance of major arthropod groups are given and compared to published data. In general, organismal biodiversity is higher in less intensely cultivated habitats. Apart from the impact of biocides, variation in species diversity often depends on the biodiversity of the surroundings (mosaic landscape) rather than on differing management regimes. The focus in preserving or enhancing, but also in evaluating biodiversity in cultivated areas thus should clearly be on the landscape level. Structural biodiversity in agricultural areas appears to be correlated with functional and organismal biodiversity of the above-ground insect fauna. (C)1999 Elsevier Science B.V. All rights reserved.