Medium- to large-bodied mammal surveys across the Neotropics are heavily biased against the most faunally intact assemblages

Biodiversity inventories provide critical information on the ecology of natural ecosystems and inform conservation planning at local to regional scales. Based on a systematic review, we compiled data on over 1000 mammal inventories conducted throughout the Neotropics – from Mexico to Argentina – to document the status of assemblage-wide field mammalogy in the world’s most biodiverse Tropical realm. We analysed data using descriptive statistics and a confusion matrix to understand the prevalence of species' pseudo-absences, map overall patterns of survey density, and quantify any geographic sampling bias. Based on the 1028 site-specific inventories published between 1983 and 2020, mean species richness of medium- to large-bodied mammals was 11.9 (± 8.8 standard deviation). Local inventories were distributed across elevational gradients, and overall sampling effort and survey techniques employed were extremely variable. The best-sampled regions were the Brazilian Atlantic Forest and Mesoamerica, but we identified nine large assemblage-wide Wallacean shortfalls and a pseudo-absence rate of 11% (± 4% standard deviation); geographic sampling bias was largely related to human population density, regardless of the assemblages’ intactness presumably found in the undersampled wilderness regions of the Neotropics. We document the 40-year legacy of mammal field surveys throughout the Neotropics, where several glaring knowledge shortfalls still persist. This calls for an audacious research agenda for future Neotropical mammal studies, which should target sampling in more remote areas, standardise sampling methodology, and provide high-resolution data that can be used to fill current knowledge shortfalls. To do so, Latin American countries and the wider international community will need to commit greater personnel and financial resources to understanding biodiversity patterns and processes related to the Tropical vertebrate fauna.