Linking species local trends from assemblage monitoring to global extinction risk.

While biodiversity is being reshaped across the globe, extinction risk assessments are lacking for most species, and a major challenge remains in understanding whether global threat status aligns with local population trends. Here, we assess whether population temporal prevalence trends are consistent with a species' global extinction risk, using over 60,000 populations of 2362 species across 978 marine and terrestrial assemblages (sampled for at least 20 years, mostly from temperate regions). We assign each population to one of five categories of temporal prevalence dynamics, and retrieve each species' extinction risk from the International Union for Conservation of Nature (IUCN) Red List. Fewer than 10% of local populations show consistent increasing or decreasing prevalence over time, with most exhibiting random patterns of temporal change, especially marine populations. Overall, higher extinction risk is associated with a higher frequency of decreasing local prevalence, and vice-versa for increasing prevalence, against a backdrop of complex links between extinction risk and local temporal dynamics. Our results suggest that directional changes in species local prevalence could be harbingers of future changes in global threat status, and highlight how leveraging assemblage monitoring data can aid conservation efforts and extinction assessments.