Title : Functional traits of carabid beetles reveal seasonal variation in community assembly in 1 annual crops

24 1. Trait-based community assembly studies have mostly been addressed along spatial 25 gradients, and do not consider explicitly a fundamental dimension governing community 26 assembly, the time. Nevertheless, such consideration seems particularly necessary in systems 27 in which organisms have to face regular disturbances and rapid changes in vegetation 28 phenology, such as in intensively managed farmlands. 29 2. In this study, we aimed at understanding how the functional diversity of carabid beetle 30 communities varied across the growing season in response to crop type. We tested three 31 alternative hypotheses on mechanisms underlying the community assembly. 32 3. We used data from a long-term monitoring conducted over nine years in an intensively33 managed farmland in central western France, in a total of 625 fields. First, we measured 34 morphological traits related to body size, dispersal mode, and resource acquisition on the 13 35 dominant carabid species (> 85 % of all trapped individuals) and identified three independent 36 dimensions of functional specialization within our species pool along axes of a PCA and 37 highlighted key traits for community assembly. Second, we evaluated the community 38 assembly temporal dynamics and the impact of habitat filtering and niche differentiation in 39 the different crop types with time, using linear mixed-effects models. 40 4. We showed that functional species assembly of carabid beetle communities occurring in 41 crop fields varies importantly intra-annually, with strong variations in these dynamics 42 depending on crop type and crop phenology. Each crop acted as a filter on carabid 43 communities for body size and resource-acquisition traits, and functional differentiation 44 between crops increased with time. We did not find any evidence of habitat filtering on traits 45 related to dispersal mode. 46 5. Our results emphasize the major role of crop phenology but also disturbances involved by 47 agricultural practices such as crop harvesting on changes in community assembly, likely due 48 . CC-BY-NC-ND 4.0 International license available under a (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made The copyright holder for this preprint this version posted February 5, 2021. ; https://doi.org/10.1101/2021.02.04.429696 doi: bioRxiv preprint