Global earthworm distribution and activity windows based on soil hydromechanical constraints

Abstract

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. Here, the authors present a mechanistic model of how soil bioturbation and climate interact to predict the global distribution of habitats and associated temporal windows of earthworms. Their models show that seasonal activity windows are predicted by soil mechanical states governed by\xa0precipitation level and distribution estimates are affected by habitat fragmentation, and highlights areas for potential earthworm migration and regions sensitive to climate.