Carabid beetles have hump-shaped responses to disturbance and resource gradients within agricultural landscapes

Understanding the effects of the huge diversity of cropping systems on local biodiversity is challenging but necessary to implement agroecological systems. Through a functional approach, the translation of cropping systems into resource and disturbance gradients is a promising way to decipher the relationship between cropping systems and biodiversity but has never been implemented for arthropods. To investigate the contributions of resource and disturbance gradients arising from cropping systems vs environmental context (regional effect, meteorological conditions and landscape characteristics) on beneficial arthropod communities, we used a dataset collected in 60 crop fields from three French areas over a 5-year period. It includes all farmer interventions, crop sequences, meteorological data, landscape composition and carabid samplings. We found that environmental context contributed to about 75% of explained carabid variations on average, while resource and disturbance gradients contributed to about 25% of explained carabid variations. The resource and disturbance gradients were particularly important in winter and in the spring preceding the spring-summer period to determine carabid variations. Moreover, we identified thresholds above which resource and disturbance gradients start being beneficial or detrimental for carabids. For example, increased treatment index in spring decreased the total activity density of carabids during the spring-summer period. Synthesis and applications. While implementing for the first time a functional approach to understand the effects of different facets of cropping systems on arthropods, our study also allows us to identify periods and thresholds above which specific practices affect carabids. Finally, avoiding bare soils all along the year, keeping pesticide use intensity below the identified thresholds and adopting a wide diversity of tillage strategies at the landscape scale should all contribute to enhance in-field carabid occurrences and richness.