Sequential Thresholds Shape Drylands' Multitrophic Response to Aridification

TL;DR

The study finds that biodiversity in drylands drops abruptly at certain aridity thresholds, with losses varying by species type and worsened by human activity.

Contribution

The paper reveals sequential aridity thresholds affecting biodiversity across multiple trophic levels in drylands, with novel insights into herbivore and detritivore vulnerability.

Findings

All taxonomic and trophic groups show abrupt biodiversity declines at aridity thresholds between 0.45 and 0.95.

Biodiversity losses range from 19% to 54.3%, with herbivores and detritivores most affected in semi-arid regions.

Human disturbance and land-use change exacerbate biodiversity losses, while primary productivity offers partial buffering.

Abstract

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.

We analyzed biodiversity responses across 290 global dryland ecoregions and found that all taxonomic and trophic groups, from microbes to mammals, showed abrupt threshold declines with increasing aridity. Thresholds varied (aridity 0.45–0.95), leading to 19%–54% biodiversity losses, most strongly in herbivores and detritivores and further exacerbated by land‐use change. While primary productivity and lower trophic richness provided some buffering, effective biodiversity conservation will require reducing anthropogenic pressures in drylands.

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