Relative effects of landscape composition and configuration on multi-habitat gamma diversity in agricultural landscapes

- Carabid gamma diversity was influenced by landscape composition and configuration.
- Plant gamma diversity was affected by landscape composition only, not configuration.
- Carabid diversity benefited from adjacencies between grasslands and crop fields.
- Increasing habitat availability (e.g. grasslands) would enhance plant species richness.
- Multi-habitat gamma diversity measures provided more general insights for actions.

Landscape composition and configuration are considered important factors influencing biodiversity in agricultural landscapes. Evaluating the relative importance of each component is complicated because they are often correlated. Overcoming this problem could lead to a better understanding of the mechanisms that drive biodiversity and help to determine effective actions. Usually, landscape-biodiversity relationships are studied at the local scale for a single habitat type (alpha diversity). However, for a better understanding of ecological processes at the landscape scale, it is also important to look at the overall diversity at the landscape level, including all habitat types. The present study was conducted to determine the relative effects of landscape composition and configuration on multi-habitat gamma diversity of carabid beetles and vascular plants in an agricultural region of western France. Twenty 1 km2 landscapes were sampled for plants and carabids. Data from 10 sampling sites representing crop fields, grasslands and woody covers in each landscape were pooled to obtain the total multi-habitat gamma diversity. Results showed that both landscape composition and configuration influenced carabid communities, while only landscape composition affected plant communities. Carabid species richness increased with increasing length of edge between crops and grasslands. Plant richness was negatively and positively affected by the percentage of crops and grasslands respectively. Carabid species composition was more dissimilar between landscapes with increasing difference in percentage of woody covers and crops, and length of grassy-crop edge. Plant species composition was more dissimilar between landscapes with a greater difference in percentage of crops. These results suggest grassy-crop adjacencies may enhance processes of resource complementation between habitats for carabids, while habitat availability and quality are the main factors for plants. This approach provided new insights for sustaining overall biodiversity in agricultural landscapes: e.g. encourage adjacencies between grasslands and crop fields and continue to subsidise grasslands for plant diversity.