Direct and indirect effects of landscape and field management intensity on carabids through trophic resources and weeds

Abstract

1. Carabids are important biological control agents of weeds and other pests in agricultural fields. The carabid community is built upon direct and indirect ecological effects of landscape complexity, field management intensity and biotic components that in interaction make any prediction of community size and composition challenging.2. We analyse a large-scale sample of 60 European cereal fields using structural equation modelling to quantify the direct effects of field management intensity and the surrounding landscape, and their indirect effect via biotic components, on carabid diversity.3. Our results highlight that direct and indirect effects of increasing landscape complexity, mediated by trophic resources, mainly affect carabids positively. Field management intensity only ever affects carabids through indirect effects that are generally negative, by suppressing standing weeds and weed seeds.4. Indirect effects on granivore carabid species depended on weed seed availability, whereas omnivores depended on the availability of both weed seeds and animal prey. Synthesis and applications.A consideration of both the direct and indirect effects of landscape and field management is necessary for predicting carabid communities. These indirect effects, mediated via trophic resources, supports the diversity and abundance of carabid communities and their provision of ecosystem services.Our results show that promoting crop diversity and connectivity to semi-natural habitats will directly enhance carabid communities in farmland by manipulating their migration from source habitats and indirectly by promoting the presence and diversity of their trophic resources. A reduction in field management intensity will preserve local standing weeds and weed seeds, and indirectly support carabid communities. These local and landscape modifications could contribute to improve the natural regulation of pests and weeds by carabids.

Seed choice in ground beetles is driven by surface-derived hydrocarbons

“…The active selection of desirable seeds can be constrained, or even abandoned altogether, depending on habitat properties and/or composition of the seed bank [80][81][82] . The biotic and abiotic properties of carabid habitats affect the abundance of plant and animal foods, as well as the microclimatic and microsite conditions 83,84 , which can profoundly affect the composition and structure of the carabid community in the field. This, in addition to factors relating to physical seed traits, fear, and dominant species in the carabid community can all render the search for desirable seed species more laborious or less rewarding to carabids foraging under field conditions 85,86 .…”

Converting cropping systems into seasonal habitat functionality reveals the hump-shaped responses of carabid beetles to agricultural management

“…Aviron et al, 2005; Trichard et al, 2013). Additional descriptors describing landscape configuration might increase the effects of landscape on carabid variations (Martin et al, 2019; Carbonne et al, 2022).…”

“…tillage intensity (Shearin et al, 2007), fertilisation type (Aguilera et al 2021) or pesticide use intensity (Geiger et al, 2010). Some studies described local habitat quality for carabids without using information on farming practices, for example with estimates of in-field available trophic resources (Carbonne et al, 2022) or proxies for habitat productivity and disturbance (Eyre et al, 2013). This body of literature yielded mixed results; probably because 1) they only tested simple linear responses of carabids to variations of habitat conditions while their responses could have quadratic shapes and 2) they did not account for the sheer diversity of cropping systems found in arable landscapes.…”

Legacy of landscape crop diversity enhances carabid beetle species richness and promotes granivores

“…Habitat patches without intensive agricultural management such as unmanaged field margins or permanent grasslands are also essential for the survival of eggs and beetle larvae, which are key to the persistence and long-term survival of ground predators (Lövei and Sunderland, 1996). Adults are also susceptible to disturbances of the soil associated with intensive crop management such as tillage due to direct mechanical injury or indirectly by reducing the availability of alternative prey (Carbonne et al, 2021;Ganser et al, 2019;Tamburini et al, 2016). However, some carabid beetles and rove beetles also benefit from high turnover of crops over time (Bertrand et al, 2016) and recently disturbed habitats (Boetzl et al, 2022).…”