Multivariate ordination identifies vegetation types associated with spider conservation in brassica crops

Conservation biological control emphasizes the importance of vegetation other than the focal crop for providing natural enemies with refuge and shelter against disturbance. There is an unmet need for better methods to identify types of vegetation that are optimal to support specific natural enemies that may colonize into crops. Here we explore the commonality of the spider fauna of brassica crops with that of adjacent crops of other species and non-crop vegetation, employing spatial-based multivariate ordination approaches, hierarchical clustering and spatial eigenvector analysis. The small-scale mixed cropping and high disturbance frequency of southern Chinese vegetation farming offered a setting to test the role of alternate vegetation for spider conservation. Our findings indicate that spider families differ markedly in occurrence with respect to vegetation type. Grassy field margins, non-crop vegetation, taro and sweetpotato offer the best opportunity for promoting spider taxa that are also brassica-active species. In contrast, pumpkin and litchi contain species not found in brassicas, and so may have little benefit for conservation biological control services for brassicas. Our findings also illustrate the potential utility of advanced statistical approaches for identifying spatial relationships of species and identify the land uses most likely to offer alternative habitats for spider conservation biological control efforts and generates testable hypotheses for future studies.