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Aim Information on change in species’ environmental preferences (i.e., niche) is currently not included in IUCN Red List criteria, although such information is key for assessing whether species not only lose geographic range but also lose part of their realized niche. Here, using niche size quantification and niche-based species distribution models (SDMs), we test whether realized niche size and predicted potential range size provide additional information compared with the standard IUCN scores. Location Switzerland, national scale. Methods We simulated randomly, spatially directed, and ecologically directed local extinction events of varying magnitudes (10%, 30%, and 50% of occurrences). For a set of 148 representative vascular plant species, we tested how accurately the geographic versus niche measures pictured these extinction scenarios respectively. Results We found that changes in niche size often corresponded to changes in geographic space. However, there was considerable variation and, for many species, changes in geographic and in niche space delivered complementary information. IUCN criteria based on spatial projections of SDMs did not capture extinction events in most cases and often increased the modelled range size, even when up to 50% of the occurrences were removed by simulated extinction events. Main conclusion Our findings demonstrate that changes in niche size can provide valuable additional information and could be used more systematically to complement changes in range size for Red List assessments. In turn, change in SDM-predicted range size was not a good surrogate for classical extent of occurrence and area of occupancy criteria and should be used with caution. Further research is needed to assess whether and how spatial predictions of SDMs may be used to appropriately complement current IUCN criteria and to test whether our findings apply to other organisms and other spatial extents.