Global earthworm distribution and activity windows based on soil hydromechanical constraints

Earthworm activity modifies soil structure and promotes important hydrological ecosystem functions for agricultural systems. Earthworms use their flexible hydroskeleton to burrow and expand biopores. Hence, their activity is constrained by soil hydromechanical conditions that permit deformation at earthworm’s maximal hydroskeletal pressure (≈200kPa). A mechanistic biophysical model is developed here to link the biomechanical limits of earthworm burrowing with soil moisture and texture to predict soil conditions that permit bioturbation across biomes. We include additional constraints that exclude earthworm activity such as freezing temperatures, low soil pH, and high sand content to develop the first predictive global map of earthworm habitats in good agreement with observed earthworm occurrence patterns. Earthworm activity is strongly constrained by seasonal dynamics that vary across latitudes largely due to soil hydromechanical status. The mechanistic model delineates the potential for earthworm migration via connectivity of hospitable sites and highlights regions sensitive to climate.


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Earthworms activity modifies soil structure and promotes ecological and hydrological soil functioning. Earthworms use their flexible hydroskeleton to burrow and expand biopores, hence their activity is constrained by soil hydromechanical conditions that permit deformation at earthworm's maximal hydroskeletal pressure (! 200 kPa). A novel biophysical model links earthworms' biomechanical limits with bioturbation permitting soil conditions across biomes and climate regions. We inject additional constraints such as freezing temperatures, soil pH, and high sand content that exclude earthworm activity to develop the first predictive global map of earthworm habitats in good agreement with observations. Earthworm activity is strongly constrained by variable seasonal patterns across latitudes. The mechanistic model delineates potential for earthworm migration and regions sensitive to climate and land use changes.
No samples were taken for this study.
No samples were taken for this study.
). For each geographic location we then evaluate the parametrized model using soil textural information from SoilGrids digital soil maps30 and monthly averaged soil moisture estimates from ERA5-land (https://doi.org/10.24381/cds.68d2bb30). All global raster data was harmonized to a common grid of 0.1°resolution (~11 km) using nearest neighbor interpolation of the upper most soil depth layer (0-5cm and 0-7 cm for SoilGrids and ERA-5 land, respectively). The limiting pressure (equation (2)) was calculated for the entire record of the ERA5-land dataset that ranges from 1981 to 2019 at a monthly resolution. We compared our theoretically determined regions with previously published empirical maps that outline earthworm distributions for Australia15 and North America16 and with presence-only data of ten earthworm species ( All global raster data was harmonized to a common grid of 0.1°resolution (~11 km) using nearest neighbor interpolation of the upper most soil depth layer (0-5cm and 0-7 cm for SoilGrids and ERA-5 land, respectively). The limiting pressure (equation (2)) was calculated for the entire record of the ERA5-land dataset that ranges from 1981 to 2019 at a monthly resolution. Based on the limiting pressure time series, we estimate the number of consecutive months below 200 kPa and the ensemble average pressure for every grid cell. A comparison of averaging methods is reported in the Supplementary Information and we reported harmonic averages throughout the main text. Two specific regions were selected to illustrate temporal activity windows: a grassland located at 9.55oN, 14.65oE and a desert located at -22.95oN, 132.95oE. We aggregated the limiting pressure time series to climatic monthly values and compared with daily climatic precipitation estimates obtained from MSWEP33. Daily precipitation estimates were smoothened using a 30-day rolling average for comparison with monthly pressure values and to delineate time windows of earthworm burrowing activity No data was excluded in this study.
All data used in this study is available from public sources. Data underlying maps of potential earthworm habitats will be deposited in a public repository upon publication (meanwhile it is available from the corresponding author upon request). As such, this will be reproducible.
This is not relevant to our study. We base our analysis on a physical model. We are not conducting a comprehensive statistical study. This is not relevant to our study. We base our analysis on a physical model. We are not conducting a comprehensive statistical study.