Grassland beetle occupancy and abundance responses to habitat, landcover, and management

Insects are vital components of grasslands; they structure plant communities, alter soil conditions, translocate nutrients, and enhance carbon sequestration. Understanding how grassland insects respond to habitat features and management practices can inform grassland conservation, however grassland insect ecology is poorly resolved. We investigated how Scarab (Scarabaeidae) and Carabid (Carabidae) beetle occupancy and abundance was impacted by local habitat features and management practices in Black Belt Prairies of Alabama. We collected beetles from 24 sites and generated occurrence and abundance data to construct single-species occupancy models for individual species and a multi-family abundance model. We utilized Stochastic Search Variable Selection (SSVS) to identify covariates associated with occupancy or abundance and estimate the effect size of those covariates. We detected 120 carabid species and 144 scarab species; of the detected species, 50 had enough observations across sites and surveys to be analyzed in occupancy models. 37 of the modelled species had at least one biologically relevant relationship with a covariate flagged by SSVS. We found vegetation diversity was positively associated with occupancy probability for 24% of modelled taxa. Further, density of invasive fire-ant mounds was negatively associated with 8% of modelled species. Land-cover influenced occupancy, but the direction of the relationship varied between species. Our models did not identify any covariates as associated with carabid abundance, but basal area had a negative influence on scarab abundance. These results identify factors impacting the distribution and abundance of ecologically and taxonomically diverse insect families and can help inform grassland conservation and restoration.