Marrec, R. | Search bioRxiv

bioRxiv2023

Taxonomic and diet-based functional structure of carabid communities varies seasonally in cultivated fields

O_LIAgricultural intensification has altered the provision of natural bioregulation. We assessed the effects of five different crops under non-inversion tillage on the temporal dynamics of carabid assemblages. We evaluated how the taxonomic diversity, the composition, and the diet-based functional structure of communities varied over the spring period. C_LIO_LICarabid assemblages were monitored over 4 years (from 2009 to 2012), in a total of 67 fields (each field followed one year) cropped with either winter oilseed rape, winter wheat, sugar beet, spring barley, or spring pea. We assigned a relative diet profile to each species accounting for more than 0.5 % of the total mean abundance-activity: granivorous, phytophagous, and zoophagous. C_LIO_LIThe seasonal changes in species richness, abundance-activity, and evenness had the same dynamic in all crops. Despite differences in species identities between crops, the zoophagous and phytophagous diet profiles showed similar temporal dynamics in all crop types, suggesting a high functional equivalence among species present in cultivated fields. Zoophagous species were progressively replaced by primarily phytophagous species in all crops, while the increase in granivorous species was only observed in oilseed rape. C_LIO_LIOur results suggest that potential bioregulation do not significantly differ among crop types but vary along the spring season. C_LI HighlightsO_LIWe monitored carabid communities in five crop types under non-inversion tillage C_LIO_LIWe observed similar seasonal increases in carabid abundance-activity and species richness in all crops during the spring period C_LIO_LIWe observed similar trends in temporal changes in carnivorous and phytophagous diet profiles in all crops C_LIO_LIWith seasonal changes, zoophagous species are progressively replaced by more phytophagous species C_LIO_LICrop type is not the main factor driving temporal changes in diet-based structure of carabid assemblages C_LI

ecology↗

bioRxiv2021

Functional traits of carabid beetles reveal seasonal variation in community assembly in annual crops

O_LITrait-based community assembly studies have mostly been addressed along spatial gradients, and do not consider explicitly a fundamental dimension governing community assembly, the time. Nevertheless, such consideration seems particularly necessary in systems in which organisms have to face regular disturbances and rapid changes in vegetation phenology, such as in intensively managed farmlands. C_LIO_LIIn this study, we aimed at understanding how the functional diversity of carabid beetle communities varied across the growing season in response to crop type. We tested three alternative hypotheses on mechanisms underlying the community assembly. C_LIO_LIWe used data from a long-term monitoring conducted over nine years in an intensively-managed farmland in central western France, in a total of 625 fields. First, we measured morphological traits related to body size, dispersal mode, and resource acquisition on the 13 dominant carabid species (> 85 % of all trapped individuals) and identified three independent dimensions of functional specialization within our species pool along axes of a PCA and highlighted key traits for community assembly. Second, we evaluated the community assembly temporal dynamics and the impact of habitat filtering and niche differentiation in the different crop types with time, using linear mixed-effects models. C_LIO_LIWe showed that functional species assembly of carabid beetle communities occurring in crop fields varies importantly intra-annually, with strong variations in these dynamics depending on crop type and crop phenology. Each crop acted as a filter on carabid communities for body size and resource-acquisition traits, and functional differentiation between crops increased with time. We did not find any evidence of habitat filtering on traits related to dispersal mode. C_LIO_LIOur results emphasize the major role of crop phenology but also disturbances involved by agricultural practices such as crop harvesting on changes in community assembly, likely due to seasonal and inter-annual redistributions of species in agricultural landscapes in response to such changes. The temporal dimension cannot be ignored to understand the assembly of local carabid communities in farmlands. C_LI

ecology↗