Joint species distributions reveal crop type and field-specific assembly rules and idiosyncrasies in carabid beetle occurrences and abundances

Abel Louis Masson , Yann Tricault, Sylvain Poggi, Lucile Muneret, Sandrine Petit, Stéphanie Aviron, Aude Vialatte, Manuel Plantegenest

1. Designing effective biodiversity conservation and pest regulation strategies in agroecosystems requires understanding how environmental gradients and assembly rules jointly structure ecological communities. 2. We fitted a hurdle joint species distribution model (jSDM) to presence–absence and conditional abundance data of 20 carabid species sampled across 57 arable fields in three French agricultural regions over five years, incorporating climate, landscape, and agricultural management covariates alongside four hierarchical random effects (sample, field, year, crop type). 3. Species distributions were primarily driven by region and temperature. Disturbance and resource gradients had little effect on occurrence, but pesticide pressure consistently reduced the conditional abundance of several species, particularly granivorous ones. 4. Beyond measured gradients, residual co-occurrence patterns revealed distinct species assemblages at both crop type and field levels. A latent crop-type gradient opposed a Brassicaceae assemblage — shaped by phenological match, trophic resources and interspecific interactions — to a maize–soybean assemblage. At field level, the idiosyncratic distribution of Carabus auratus was interpreted as a signal of extinction debt. 5. Synthesis and applications. Carabid community structure is constrained by crop type through biotic and abiotic mechanisms, with direct implications for biocontrol strategies. Short-term pesticide reduction may restore population densities without recovering species diversity, highlighting the need for abundance-based indicators of agri-environment schemes benefits. The detection of an idiosyncratic species distribution, consistent with an extinction debt, further illustrates the relevance of jSDMs for conservation in agricultural landscapes.