Late-Quaternary megafauna extinctions have strongly reduced mammalian vegetation consumption

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 x 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.