Habitat temporal complementation: How do beneficial ground beetles survive in a transient mosaic?
Résumé
Managing agricultural landscapes to enhance biological control requires an understanding of the spatio-temporal dynamics of beneficial arthropod populations. In agricultural landscapes, functional heterogeneity results from both the spatial pattern of landscape elements and their rapidly changing of habitat suitability. This suitability dynamics results first from the within-year dynamics of vegetation growth and crop management practices, and second from the year-to-year dynamics of crop rotations. We investigated the impacts of cropped habitat dynamics on population recruitment, distribution and movements of a beneficial predatory carabid beetle (Pterostichus melanarius). Our hypothesis is that populations are sustained by the beetles mobility that enables them to exploit the temporal complementarity of different adjacent crops and boundaries. The study was conducted in a mosaic of five adjacent fields of cereals and maize (total area 30 ha) in Western France. The mosaic was surrounded by roads isolating the population. Three types of sampling were done weekly from May to September 2009: 1) the field productivity in terms of post-emerged adults with enclosed emergence arenas; 2) the overall activity-density of carabid beetles in open pitfall-traps and 3) the exchanges between fields and their field boundaries and adjacent fields, with directional barrier traps.