Abstract
Aim Amid ongoing and accelerating global change, predicting the ecological consequences of future species loss is important for prioritising conservation actions to protect biodiversity. Species richness has long been thought to protect communities from species loss by providing ecological redundancy, whereby the loss of any one species hardly impacts the integrity of the wider community due to overlap in species' ecological roles. However, the extent to which species richness will buffer the impacts of future species loss remains unclear due to concurrent variation in both the distribution and ecological roles of species likely to be lost. Location Canada. Taxon Terrestrial vertebrates. Methods To understand how future species loss threatens ecosystems and whether species richness mitigates this threat, we simulated the loss of imperilled taxa from Canadian ecosystems across spatial scales and measured the extent to which community functional and interaction (predator–prey) diversity, two important components of ecosystem integrity, declined. Results We report that, despite harbouring far fewer species at risk, northern ecosystems are disproportionately vulnerable, whereby the loss of imperilled taxa could result in up to 25% and 20% declines in functional and interaction diversity, respectively. Surprisingly, despite high species richness, some southern ecosystems containing high numbers of imperilled taxa were also vulnerable, indicating that richness alone is likely insufficient at predicting community vulnerability to species loss. Main Conclusions Together, these findings demonstrate the need to account for future species loss when evaluating the vulnerability of Earth's ecosystems and highlight the importance of conserving species at risk, specifically in northern communities where they potentially play outsized roles in structuring and maintaining the integrity of ecosystems.