Linyphiid spider populations in sustainable wheat-clover bi-cropping compared to conventional wheat-growing practice

摘要

Linyphiid web densities in wheat-clover bi-crop systems where winter wheat was grown in an under-storey of white clover were compared with web densities estimated in conventional wheat-growing systems. The web densities in the wheat-clover bi-crop systems were on average between 200 and 250 webs per square-metre when the densities peaked, while the estimated average web density peak levels under conventional growing practices were 100-150 webs per square-metre. Repeated Measure anova tests show significant differences between the estimated mean web density levels of the bi-crop systems compared to the mean density levels of the conventional growing systems in two consecutive growing seasons. Particularly, Bathyphantes gracilis and Tenuiphantes tenuis took advantage of the more heterogeneous conditions with high secondary vegetation layer density and high food animal supply in the bi-crop plots compared to the more homogeneous conditions under conventional wheat-growing practices with low food animal supply. Structural equation modelling with a data set pooled from four different wheat-growing practices shows that the linyphiid juvenile production is influenced by the number of collembolans accessible as food animals for the adult females. The modelling demonstrates the importance of the detritus food chain, particularly for the juvenile recruitment.