Megafauna diversity and functional declines in Europe from the Last Interglacial to the present

<b>Aim:</b> Reconstructing megafauna diversity in a past before anthropogenic impacts is crucial for developing targeted restoration strategies. We estimated the diversity and functional decline of European megafauna in the present compared to the nearest in time climate period analogue to the present but prior to the worldwide diffusion of Homo sapiens.<b>Location: </b>Europe.<b>Time period: </b>Last Interglacial (LIG; ca. 127,000 years ago) to present.<b>Major taxa studied: </b>Wild, large (≥10 kg) terrestrial mammals.<b>Methods: </b>We assessed the distribution of 48 European megafauna species during the LIG using hindcasting modelling and fossil records. Then, we estimated the decline in megafauna community diversity and potential trait-based functional effects from the LIG to the present, accounting for climate differences between the two periods.<b>Results: </b>Species richness and community biomass dropped by 70.8% (± 11.7%) and by 94.5% (± 9.9%). Functional diversity dropped by 80.3% (± 15.3%) for herbivores and by 64.9% (± 29.1%) for carnivores, while trait-informed potential vegetation and meat consumptions dropped by 82.3% (± 13.4%) and 60.5% (± 26.0%). The loss in megafauna diversity and associated ecological processes were high everywhere, but particularly in western Europe for carnivores and in the East European Plain for herbivores. Potential megafauna richness in the two periods were similar if only climate-driven differences were considered.<b>Main conclusions: </b>Severe, size-biased defaunation has degraded megafauna assemblages and megafauna-mediated ecological processes across Europe from the LIG to the present. These patterns cannot be explained by climate differences between the two periods, thus were likely driven by prehistoric Homo sapiens. The results suggest that the structure of wild ecosystems of the present strongly deviates from the evolutionary norm, with decreased functional heterogeneity and decreased fluxes of biogeochemical compounds across the trophic networks, highlighting the importance of ambitious policies of megafauna community restoration to support ecosystems functioning.