Biogeographic Reorganization of Horse-Associated Tabanidae Assemblages in the Neotropical Region: Species Turnover, Numerical Concentration, and Seasonality

Horse flies (Diptera: Tabanidae) are hematophagous insects of veterinary importance, but how horse-associated assemblages are reorganized across Neotropical biogeographic units remains poorly integrated. We compared 11 validated study-level assemblages to test whether richness comparisons were sensitive to unequal sample size and sampling heterogeneity (H1) and whether biogeographic differentiation was driven mainly by species replacement rather than nestedness (H2). Observed richness was not significantly associated with validated capture size or reported campaigns, but individual-based rarefaction substantially changed richness rankings. Multiple-site Sørensen beta diversity was strongly attributable to Simpson turnover in the core (94.5%) and sensitivity (94.6%) datasets, and mean turnover increased descriptively across progressively deeper Morrone biogeographic separation classes. Across seven quantitative core assemblages, median Top1, Top3, and Top5 contributions were 49.2%, 68.4%, and 81.0%, respectively, and six species occupied the Top1 position. Annual Top1 taxa retained dominance in only 50–75% of positive sampling periods in four temporally resolved studies. Thus, horse-associated assemblages differ primarily through species replacement, while most abundance is concentrated in a small, geographically and temporally variable subset of taxa. Locally and seasonally abundant species are rational first-pass targets for pathogen screening and behavioral investigation, but abundance does not imply vector competence or transmission risk.