Characterisation of carabid functional traits in different farm systems

Agricultural intensification has a major impact on arthropod diversity and related functional traits. However, research has primarily focused on how farm systems influence biodiversity metrics, often overlooking trait-mediated responses. This study examined the response of carabid beetle abundance, composition and functional traits to farming systems and vegetation cover in South African agricultural systems. Carabid beetles were collected from grain crop farms (conservation grazing, conservation tillage and conventional tillage) and semi-natural grasslands using pitfall traps and active search method. The abundance and community trait composition of the six genera were quantified using Generalised Linear Models (GLMs – Poisson and negative binomial distributions) and multivariate ordination. The relationship between traits and vegetation cover was evaluated using Generalised Additive Models (GAMs). Conservation grazing supported the highest carabid abundance, with conventional tillage and semi-natural grasslands exhibiting a significant abundance decline. Large-bodied genera, Calosoma and Scarites, showed 95% abundance decline outside conservation grazing. Community ordination indicates distinct segregation by farm type, primarily attributed to wing morphology and predatory behaviour. Functional trait responses were significantly affected by the interaction between vegetation cover and farm system, with brachypterous species responding uniformly (optimal at 25–35% cover), whereas macropterous carnivores exhibited different patterns. Conversely, semi-natural grasslands had the lowest abundance and trait results despite permanent vegetation. Overall, conservation grazing with a moderate vegetation structure provide an intact habitat for functionally important predatory carabids. These results suggest that species-specific functional traits should be identified when implementing sustainable management practices.