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Aim: Reconstructing megafauna diversity in the 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 with the nearest in‐time climate period analogue to the present but prior to the worldwide diffusion of Homo sapiens. Location: Europe. Time Period: Last Interglacial (LIG; ca. 127,000 years ago) to present. Major Taxa Studied: Wild, large (≥10 kg) terrestrial mammals. Methods: 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. Results: 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 was similar if only climate‐driven differences were considered. Main Conclusions: 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 ecosystem functioning. [ABSTRACT FROM AUTHOR]

Aim: How much stronger would the effects of herbivorous mammals be in natural ecosystems if human‐linked extinctions and extirpations had not occurred? Many mammal species have experienced range contractions, and numerous species have gone extinct in the late Quaternary, completely or in large part linked to human pressures. Therefore, herbivore consumption rates in seemingly natural ecosystems will deviate from their pre‐anthropogenic state. Here, we estimate the size of this deviation. Location: Terrestrial systems, globally. Time period: Current. Major taxa studied: All late‐Quaternary terrestrial mammals. Methods: We estimated and mapped vegetation consumption rate by all late‐Quaternary terrestrial mammals. We did this through the estimation of natural densities and dietary needs. We mapped their consumption rate in both current ranges and present‐natural ranges, that is estimated ranges in the absence of human‐linked range contractions and extinctions. We compared these estimated consumption rates to current net primary productivity (NPP). We summarized the results across ecosystem types everywhere as well as for only the last remaining wilderness areas. Results: We estimate that wild mammals consume a median of 11% of NPP (at the scale of 96.5 km × 96.5 km grid cells) in current natural areas and that this would have been much higher in the absence of extinctions and extirpations, namely 21%. Looking at the change per grid cell, the mammal losses result in a median 42% reduction in consumption rate. Importantly, we estimate very similar declines in herbivory in what are considered the last remaining wilderness areas. Main conclusions: Our results suggest that the natural interaction of mammalian herbivores with vegetation in ecosystems across the world is strongly reduced by prehistoric and historic to recent species losses, even in the last remaining wilderness areas, likely with major effects on ecosystem structure and functioning. [ABSTRACT FROM AUTHOR]