Zoogeographical realms modulate trophic constraints on bite-force disparity in Carnivora assemblages

INTRODUCTION: Elucidating the rules of community assembly is a central challenge in macroecology. Using an ecomorphological framework, we investigated how biotic gradients (dietary specialisation and habitat structure) and abiotic factors (contemporary and Last Glacial Maximum climates) interact to structure the phenotypic disparity of bite force in modern terrestrial Carnivora assemblages at a global scale. METHODS: We estimated the theoretical bite force of 136 species using a 2D lever model on dry skulls, deriving the Bite Force Quotient (BFQ) to decouple craniomandibular performance from allometry. Species distributions were projected onto a 1º Mollweide global grid (9,645 assemblages). We calculated the standardised effect size (SES) of phenotypic disparity (Rao's Q) using macroevolutionary null models (Ornstein–Uhlenbeck) to control for phylogenetic relatedness and species richness. Spatial Autoregressive Error (SARerr) models and Structural Equation Modelling (SEM) were applied to disentangle the direct and indirect pathways of historical climate, contemporary productivity (NPP), vegetation structure, and dietary specialisation (vertebrate consumption), followed by spatial decomposition across zoogeographical realms. RESULTS: Carnivoran standardised bite-force disparity is strongly geographically structured. Globally, disparity appears to be constrained by increased vertebrate consumption, whereas historical climate and NPP seem to directly expand it. Crucially, SEM supported a trophic mediation architecture: historical climate likely dictates the current dietary spectrum, and this increased reliance on vertebrate prey acts as a primary evolutionary bottleneck. Spatial models revealed significant biogeographical contingency; the Neotropical realm is unique, presenting a near-zero adjusted mean, and the strength and direction of the dietary bottleneck on bite-force disparity varied significantly across zoogeographical realms. CONCLUSIONS: The macroecological rules governing functional disparity in predatory guilds appear to be profoundly contingent upon biogeographical context. Unique regional events, such as the Great American Biotic Interchange (GABI) shaping the Neotropical fauna, may drive asymmetrical evolutionary constraints. Ultimately, deep historical legacies (acting indirectly through diet) and contemporary pressures likely interact to continuously sculpt the biomechanical landscape of carnivoran assemblages, suggesting how global zoogeographical realms can modulate functional macroecological patterns.