Deceptive diversity: Mammals in the Indian Western Himalaya face extinction debt due to global change

Abstract

The Western Himalaya harbours distinctive and rich mountain mammal assemblages, yet the persistence of species may conceal underlying ecological decline. We propose the concept of deceptive diversity, describing the period during which extinction debt accumulates but remains largely undetected as species continue to persist. Synthesising evidence from long-term population monitoring, distributional assessments, genetic studies, and recent observations of climate- and development-driven ecological change, we show that many mammals in the Western Himalaya persist as small, fragmented and peripheral populations exhibiting restricted distributions and isolation. Emerging consequences include novel species interactions, declining connectivity, reduced dispersal opportunities, and increased extinction debt, despite the continued presence of many species. We argue that biodiversity assessments based solely on occupancy or species richness risk overlooking these hidden processes of ecological erosion. Recognising deceptive diversity shifts conservation attention from documenting extinctions to identifying the early demographic and ecological warning signals that precede them. This provides a framework for proactive conservation of populations before declines become irreversible; a proposition which is relevant to other important mountain biodiversity hotspots globally.