Although anthropogenic climate change is expected to cause serious declines in biodiversity, scientific predictions of such declines are scarce and vary widely depending on specific model assumptions. One of the most important model decisions that greatly impacts estimated biodiversity declines is the characterization of species' climatic tolerances beyond the range of currently-observed climatic conditions, often referred to as the problem of truncated climate niches. We developed an environmental niche model specifically designed to estimate species tolerances to novel temperatures and applied this model to predict future climatic tolerances of over 7,000 plant species across the Amazon in the year 2070. By compiling the predictions across all species, we estimated the changes in species richness that may be expected to result from climate change by the year 2070, and how these losses in biodiversity vary spatially across the Amazon.
Predicted losses in species richness varied widely across the Amazon, ranging between 15 and 64%. Biodiversity losses due to climate change were predicted to be greatest in the Southeastern Amazon and parts of the Central Amazon, while these losses were predicted to be less in the Northwest and the Northeast. Our model estimates of future biodiversity declines differed substantially from those created using simple assumptions about species' responses to future climate conditions. Because our model explicitly estimates species' responses to novel future climatic conditions using available data, we expect that the resulting estimates of expected biodiversity declines are more reliable than those produced based on simple assumptions, but this requires further investigation to be verified. This work highlights the sensitivity of estimated future losses in biodiversity to model decisions about species climatic tolerances, and the need to make careful choices in this area. Our spatially-explicit estimates of climate-driven species losses also have important implications for the protected areas of the Amazon, including conservation units and indigenous lands.