Invisible biodiversity: extinction debts and colonization credits amongst US birds

Abstract Habitat change is a major source of biodiversity loss. However, the response of animal communities to land-cover changes is not instantaneous. In fact, extinctions and colonizations may take up a long time before they fully manifest, leading to extinction debts and colonization credits. Current quantifications of debts and credits do not consider multiple land cover types and their directionality of change. Here we quantify the relative contribution of past and present landscapes to the current species richness of 5500 USA bird communities, explicitly measuring the response of biodiversity to increases and decreases of five land covers. We identified extinctions debts across 12% of the USA whilst colonization credits were instead present in 16% of the land area. Future species loss is predicted in the East following recent urbanization, while new species colonizations are expected mainly in the North-West as a result of forests conversion into grasslands. Furthermore, lags in biodiversity response were dependent not only on the type and amount of land cover change, but also on its directionality. Effective conservation actions rely on reliable predictions of future biodiversity. Our results highlight the essential need of considering past landscape changes when setting policy targets aiming at halting biodiversity loss.