Globally invariant metabolism but density-diversity mismatch in springtails

Abstract

Soil life supports the functioning and biodiversity of terrestrial ecosystems. Springtails (Collembola) are among the most abundant soil arthropods regulating soil fertility and flow of energy through above- and belowground food webs. However, the global distribution of springtail diversity and density, and how these relate to energy fluxes remains unknown. Here, using a global dataset representing 2470 sites, we estimate the total soil springtail biomass at 27.5 megatons carbon, which is threefold higher than wild terrestrial vertebrates, and record peak densities up to 2 million individuals per square meter in the tundra. Despite a 20-fold biomass difference between the tundra and the tropics, springtail energy use (community metabolism) remains similar across the latitudinal gradient, owing to the changes in temperature with latitude. Neither springtail density nor community metabolism is predicted by local species richness, which is high in the tropics, but comparably high in some temperate forests and even tundra. Changes in springtail activity may emerge from latitudinal gradients in temperature, predation and resource limitation in soil communities. Contrasting relationships of biomass, diversity and activity of springtail communities with temperature suggest that climate warming will alter fundamental soil biodiversity metrics in different directions, potentially restructuring terrestrial food webs and affecting soil functioning.

Fig. 1. Sampling locations and latitudinal gradients in springtail community metrics.

a Distribution of the 2470 sampling sites (43,601 soil samples). The histogram shows the number of sites in each 20-degree latitudinal belt, relative to the total land area in the belt. b–g, Variation in density (n = 2210 independent sites), biomass, community metabolism, average body mass and average individual metabolism (n = 2053), and local species richness (n = 1735) with latitude. Grey circles across panels show sampling sites; red points are averages for 5-degree latitudinal belts; trends are illustrated with a quadratic function based on 5-degree averages (red line shows the mean, shaded band shows the 95% confidence interval). Source data are provided as a Source data file.

Fig. 2. Global maps overlapping modelled springtail density and local species richness and community metabolism in soil.

In (a) colours distinguish areas with different combinations of density and species richness, e.g., low density—low richness is given in yellow and high density—high richness in violet. In (b) the colour gradient indicates community metabolism, with potential coldspots shown in yellow and hotspots shown in blue. Pixels below the 90% extrapolation threshold for the corresponding variables are masked (see methods). Correlations between density or metabolism and species richness (inset graphs) are based on site-level data (points; n = 1257).

Fig. 3. Environmental predictors of springtail communities at the global scale.

Standardized effect sizes for direct (semi-transparent colour) and total (direct and indirect, solid colour) effects from path analysis are shown for density (R² = 0.36 ± 0.01, n = 723 per iteration), local species richness (R² = 0.20 ± 0.02, n = 352), biomass (R² = 0.40 ± 0.02, n = 568), and community metabolism (R² = 0.17 ± 0.02, n = 533). Mean values (squares) and data distribution (violins) are shown. Asterisks denote factors with a significant direct effect (two-tailed; p < 0.05) on a given springtail community metric for >25%(*), >50%*, >75%** and >95%*** of iterations. Source data are provided as a Source data file.