Local vs. landscape characteristics differentially shape emerging and circulating assemblages of carabid beetles in agroecosystems

Knowledge of biodiversity in agroecosystems is crucial for understanding ecosystem functioning, but requires accurate sampling methods. Most studies of ground-active arthropods in fields rely on activity-density measurement using pitfall traps. Assemblages locally observed are likely to composed both resident and immigrant species, and that is especially true for arthropods exhibiting high dispersal abilities and/or larval development that is very different from the adults. Using a spatially paired design of emerging traps vs pitfall traps in 10 pairs of organic (OF) and conventional (CF) fields, we quantified how circulating and emerging assemblages of an abundant taxa of mobile and holometabolous insects, carabid beetles, were impacted by different field farming systems and landscape characteristics. Field sampling was carried out during 5 months of 2015 in Brittany (Western France), during which 24,726 individuals belonging to 85 species were captured. Our results revealed that the number of individuals and species of both emerging and circulating assemblages were significantly higher in OF compared to CF, reinforcing the idea that OF provide more suitable conditions for both resident and mobile arthropods. Landscape and local factors had a similar influence on emerging carabid assemblages, whereas local factors were stronger drivers for circulating carabid assemblages. This study highlights the importance of distinguishing resident (emergent) and mobile (circulating) individuals when assessing the differential role of local vs. landscape factors in community assembly. It also reinforces the idea that spatiotemporal movements of predatory arthropods are impacted by spillover from and between croplands, resulting in source-sink dynamics with habitat quality being the major driver of these processes.