Elevated ENSO extremes are reducing tropical forest invertebrate diversity and function

The conservation status of invertebrates globally is uncertain1–5. In particular, information from primary tropical forests is limited3–5, and yet invertebrates are responsible for crucial processes in the ecosystem6,7 as well as being an essential food source for many vertebrates. There is currently significant debate as to whether invertebrate biodiversity is in long-term decline due to climate change4,8 or changing naturally alongside weather9,10. We demonstrate that both are true in primary tropical forests: intensified El Niño Southern Oscillation cycles under climate change11 are disrupting natural fluctuations in invertebrate diversity. We generalized species richness shifts for nine invertebrate Orders from 33 time series spanning primary forests in the Americas, Africa and Asia. The most speciose Orders were all in long-term decline, while others showed more violent fluctuations in diversity with ENSO extremes over time. El Niño appeared to drive strongest declines in those Orders which naturally increase in diversity during La Niña. In addition, we found our diversity generalizations correlated with tropical-scale reductions in rates of invertebrate driven leaf litter decomposition during El Niño events and steep leaf herbivory declines across 76 decomposition/herbivory studies. Our analyses suggest that increasingly fluctuating climate extremes immediately threaten primary forest invertebrates, their ecological functions and hence the survival of these forests. Understanding the mechanisms behind this novel threat is paramount, as is expanding future long-term monitoring of tropical invertebrate biodiversity.