A global synthesis of biodiversity responses to glacier retreat.

Glaciers cover about 10% of the Earth's land area but they are retreating rapidly and many will disappear within decades. Glacier retreat is a worldwide phenomenon increasing the threat to water resources, biodiversity and associated ecosystem services for hundreds of millions of people, mostly in developing countries. Our understanding of the ecological consequences of glacier retreat has improved significantly in the past decade, but we still lack a comprehensive framework for predicting biodiversity responses to glacier retreat globally, across diverse habitats and taxa. By conducting a global meta-analysis of 234 published studies, including more than 2,100 biodiversity surveys covering marine, freshwater and terrestrial assemblages, we show here that taxon abundance and richness generally increase at lower levels of glacier influence, suggesting that diversity increases locally as glaciers retreat. However, significant response heterogeneity was observed between study sites and species: 6-11% of the studied populations, particularly in fjords, would lose out from glacier retreat. Most of the losers are specialist species, efficient dispersers, uniquely adapted to glacial conditions, whereas the winners are generalist taxa colonizing from downstream. Our global analyses also identify key geographic variables (glacier cover, isolation and melting rates, but not latitude or altitude) and species traits (body size and trophic position) likely to modulate taxon sensitivity to glacial retreat. Finally, we propose mechanistic diagrams for model development to predict biodiversity change following glacier retreat.