A common mantra is that more data is always better, but how much is enough is complex to answer, specially when we want to capture the spatial and temporal variability of a given process. However, there is a strong trade-off between a perfect design and its feasibility. The trap design, arthropod community metrics and crops selected were the principal levers for optimizing the trade-off between sampling effort and the ability to detect arthropod community responses to cropping systems.ĭespite the increasing refinement of statistical methods, a robust experimental design is still one of the most important cornerstones to answer ecological and evolutionary questions. The minimum sampling effort required for community comparisons under different arable cropping systems was smaller for functional composition than for activity-density in case of spiders and richness in case of carabids. For the three arable cropping systems studied here, carabid activity-density, carabid CWM body size and spider genus richness were the variables better distinguishing between cropping systems with the smallest sampling effort. Fewer traps were required to find differences between cropping systems for CWM body size than for other metrics. The relationship between the arthropod community differences and the minimum sampling effort required to detect it was similar for activity-density and species or genus richness metrics. In the case of our experiment conducted in arable crops, simulations with various sampling efforts showed that only very different communities could be significantly distinguished with less than ten traps per field or less than 30 field-year replicates. The type of preserving fluid had no marked effect on any of the metrics considered. Trap size affected the observed composition of carabid and spider communities, with large traps yielding a higher relative proportion of spiders, and a higher species richness and CWM body size for both taxa. In a field experiment comparing three cropping systems, we compared the effects of two pitfall trap diameters, the type of preserving fluid used in pitfall traps and the sampling effort on six metrics describing communities: activity-density, richness and community weighted mean (CWM) of body size, each one for carabid and spiders. ![]() We evaluated the suitability of pitfall traps for characterizing the effects of arable cropping systems on the taxonomic and functional composition of spider and carabid communities. In particular, the ability to distinguish between simplified communities and the sampling effort required have been little investigated. In arable agroecosystems, arthropod communities are more simplified than in natural ones and sampling techniques need to be adjusted to these specific conditions. The sampling efficiency of pitfall traps has been widely studied in natural ecosystems. ![]() Ground dwelling arthropods are affected by agricultural practices, and analyses of their responses to different crop management are required.
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