Comparisons of temporal changes in carabid communities inhabiting five different crops

Agricultural areas are currently expanding in the world. It resulted in the decline of biodiversity, affecting ecosystem functioning and the provision of ecosystem services associated. To decrease the pressure of agricultural activities, we should better manage the ecosystem services delivered by natural enemies, such as carabids. Carabids are usually considered as providers of ecosystem functions, such as pest regulation. The objective of this study was to investigate the effect of five different crops (Wheat, Sugar beet, Oilseed rape, Pea and Barley) under non-inversion tillage on carabid communities’ dynamics during spring. We quantified three diversity indices (abundance-activity, number of species and equitability index) and used functional-trait based approach, the communities’ diet profiles, as an evaluation of the ecosystem services delivered by carabid’s community. The study was conducted every year from 2009 to 2012 in 5 sites located in the Seine et Marne region. The carabid communities were recorded from 67 fields cropped with: oilseed rape (9 fields), winter wheat (27 fields), sugar beet (12 fields), spring barley (11 fields) and spring pea (8 fields). Carabids were sampled using three replicate pitfall traps per field, each fulfilled with a saturated salt solution containing a small amount of strong detergent as a preservative. The carabids were sampled once time every month during four months, from March to June. 33 621 individuals have been trapped in 4 years and 11 carabid species represented each at least 2% of the total abundance-activity. In all crop, total abundance-activities significantly increased during the year as the number of species. Contrary to the indices related to taxonomic diversity, the equitability indices did not significantly change during the year in all sampled crops. Crops were characterised by significantly different composition of carabid species in April, May and June but not in March. Concerning the diet profile, the expression of phytophagous significantly increased while the expression of zoophagous significantly decreased with time, whatever the crop considered. Despite great differences between crops, ecosystem services delivered by carabid’s community changed similarly during spring. According to the crop studied, agricultural practices were probably not explaining changes in carabid communities and demonstrated strong influences of resources availability. The latter seemed to be the main cause of changes in diet characteristics of carabid communities. To maximise ecosystem services related to pest regulation, it seems necessary to better understand the influences of resources used by carabid in order to control their diet expression.