The effect of past defaunation on ranges, niches, and future biodiversity forecasts

Humans have reshaped the distribution of biodiversity across the globe, extirpating species from regions otherwise suitable and restricting populations to a subset of their original ranges. Here, we ask if anthropogenic range contractions since the Late Pleistocene led to an under‐representation of the realized niches for megafauna, an emblematic group of taxa often targeted for restoration actions. Using reconstructions of past geographic distributions (i.e., natural ranges) for 146 extant terrestrial large‐bodied (>44 kg) mammals, we estimate their climatic niches as if they had retained their original distributions and evaluate their observed niche dynamics. We found that range contractions led to a sizeable under‐representation of their realized niches (i.e., niche unfilling). For 29 species, more than 10% of the environmental space once seen in their natural ranges has been lost due to anthropogenic activity, with at least 12 species undergoing reductions of more than 50% of the..., To evaluate the effect of shifted baselines on estimates of sensitivity to future climate change—measured in terms of potential distribution variation—we used ecological niche models based on different assumptions. The first scenario assumes that species’ distributions are in equilibrium with the environmental conditions across their ranges today and uses climatic information solely from species’ current ranges to calibrate ecological niche models, which we call current‐based models. The second scenario relies on climatic information from species’ natural ranges, that is, simulating a scenario where species have never experienced heavy anthropogenic stressors (Faurby & Svenning, 2015). The latter considers that fundamental niches tend to be conserved over time (Peterson, 2011) so that occurrence records from different periods should provide additional information on species’ climatic tolerances from environments without contemporary counterparts (Faurby & Araújo, 2018; Lima‐Ribe..., File List: 
1) Current_based_future_binary.rar maps of species' future potential distribution, calibrated with environmental information from species' current ranges (available as Current_PHYLACINE.rar)
2) Current_PHYLACINE.rar maps of species' current realized distribution, obtained from PHYLACINE dataset
3) Present_natural_future_binary.rar maps of species' future potential distribution, calibrated with environmental information from species' present natural ranges (available as Present_natural_PHYLACINE.rar)
4)Present_natural_PHYLACINE.rar maps of species' present natural distribution, obtained from PHYLACINE dataset
Relationship between files:  Present natural ranges depict the locations species might have occupied in the present, had they not been affected by human presence. Current ranges depict the locations species are known to occupy in the present.