Speaker
Description
Introduction. At the landscape scale, agricultural intensification resulting from the loss of semi-natural habitats, reduction in land-cover diversity and increase in field size is a major threat to biodiversity and the delivery of ecosystem services (1, 2). In addition, climate change has an increasing role in the decline of biodiversity (3–5) and is posing a growing threat to agriculture and food security (6). Increasing the quantity of semi-natural habitats (e.g. hedgerows, grasslands) and landscape heterogeneity (in terms of composition, e.g. diversity of land-use types, and of configuration, e.g. density of edges between different land-cover types) could help mitigate the loss of biodiversity and its associated ecosystem services. Landscape can directly affect biodiversity by providing different habitats and resources (i.e. food, refuge) around the fields and by promoting the dispersal and colonization in field of organisms. Landscape can also have indirect effects by modifying mesoclimate, and especially air temperature. Carabid beetles are abundant and widespread natural enemies of insect pests and weed seeds in arable fields, thus playing a key role in agricultural landscapes (7, 8). They also are known to be dependent on landscape (9) and local abiotic [e.g. farming practices (10)] and biotic [e.g. standing weeds(11)] factors. In the present study, we tested the hypothesis that in combination with local drivers (farming practices and weed cover), landscape has a direct and indirect (mediated through mesoclimate) effect on carabid beetle communities and has a consequence on weed seed predation. We focused on winter cereal fields, which represents the most important crop in Brittany.
Materials, methods. We selected twenty 1 km × 1 km landscape windows along uncorrelated gradients of semi-natural habitat amount and landscape heterogeneity. For each landscape window, we recorded air temperature through automatic sensors. We sampled 77 fields within these landscape windows, where we monitored carabid beetle communities and seed predation for two weed species (Viola arvensis and Poa annua). SEMs were built to test for the direct and indirect effect of landscape structure on carabid beetle richness, activity-density and composition, and on weed seed predation, for two sampling time (May and June 2023).
Results. In May, the activity-density of granivorous and omnivorous carabids increases with a high amount of grasslands, a low amount of hedgerows. It depends also on farming practices. Their composition depends on both compositional heterogeneity and farming practices. In June, the richness of granivorous and omnivorous communities increases with a high weed cover whereas activity-density increases with a high amount of grasslands. Their composition depends on grassland and hedgerow amount, maximum air temperature and weed cover. We found an indirect effect of landscape on carabids mediated by mesoclimate. A high amount of grassland increases the maximum air temperature, which in turn affects the composition of granivorous and omnivorous carabid communities. Lastly, we found cascading effects of the richness and/or activity density and/or composition of communities affects the predation of Viola arvensis and/or Poa annua.
Discussion. These results highlight grasslands' importance for carabid beetles as a source habitat providing resources, sites for reproduction and overwintering and refuge from in-field disturbances. Additionally, they reveal that grasslands can increase air temperature, particularly in late spring (July), likely due to reduced vegetation height after grazing or mowing. Increase in air temperature affects carabid beetle composition, likely by influencing traits related to thermotolerance. Overall, grasslands play a key role in agricultural landscapes, affecting directly and indirectly (by modifying maximum air temperature), carabid communities and the weed regulation service they support.
References.
1. T. Newbold et al., Nature (2015).
2. T. Tscharntke et al., Ecol. Lett. (2005).
3. T. Newbold, Proc. R. Soc. B Biol. Sci. (2018).
4. H. M. Pereira et al., Annu. Rev. Environ. Resour. (2012).
5. F. Sánchez-Bayo et al., Biol. Conserv. (2019).
6. K. Wiebe et al., Sustainable Food and Agriculture (2019)
7. S. S. Kulkarni et al., Weed Sci. (2015).
8. G. L. Lövei et al., Annu. Rev. Entomol. (1996).
9. B. A. Woodcock et al., Agric. Ecosyst. Environ. (2010).
10. S. Navntoft et al., Agric. For. Entomol. (2006).
11. P. Saska et al., Sci. Agric. Bohem. (2014).
| Keywords | landscape; climate; weed seed predation; plant-animal interactions; agricultural practices |
|---|
