Sequential Thresholds Shape Drylands' Multitrophic Response to Aridification.

Drylands, supporting significant global biodiversity, exhibit abrupt, non-linear responses to increasing aridity with drastic declines after threshold crossing. While plant and soil responses are documented, impacts on other organisms remain unclear, as well as their potential interactions with other anthropogenic drivers. We investigated changes in taxonomic and trophic richness of multiple organisms, from bacteria to mammals, in response to aridity across 290 dryland ecoregions globally. All groups showed sequential threshold responses to aridity with threshold values ranging from 0.45 to 0.95 aridity levels, resulting in varying biodiversity losses (19%-54.3% depending on trophic group) after crossing such thresholds. Responses were most widespread in hyper-arid and arid regions, primarily affecting herbivores and detritivores in semi-arid areas, and were exacerbated by human disturbance and land-use change. However, primary productivity and richness of primary producers and prior trophic levels partially buffered these declines. Biodiversity conservation and reducing anthropogenic pressures can mitigate these losses.