Climate change could have serious implications for earthworm communities, according to the first global earthworm map published on 24 October in Nature (1).
Earthworms are arguably one of the most important groups of animal on the plant and key components of land-based ecosystems. Sometimes referred to as ‘ecosystem engineers’, they are responsible for cycling nutrients throughout soil ecosystems, decomposing organic matter, and mixing soil elements, among other important functions. This might be why there are so many worms — the total earthworm biomass of area is often much larger than the total biomass of all mammals in the same area.
First earthworm atlas
Starting in 2016, the team of researchers led soil ecologist Dr Helen Phillips at the German Centre for Integrative Biodiversity Research (iDiv) in Leipzig, began contacting researchers around the globe and asking for their data on earthworms.
First, they compiled data provided by 140 researchers and evaluated the data to ensure it was comparable from site to site. And finally, used computer modelling to create a global map. Now, this first-ever global atlas of earthworms combines global data on earthworm diversity, abundance, and biomass from 6928 sites in 57 countries.
Senior authors Prof Nico Eisenhauer of iDiv and Dr Erin Cameron or Saint Mary’s University in the UK said they were surprised and delighted by how much data researchers were willing to share.
The map shows that belowground biodiversity typically increases from low to high latitudes, which is the opposite of patterns observed for aboveground species, such as birds, insects, and plants. More specifically, local earthworm diversity is highest in more temperate regions like Europe, northeastern USA, and New Zealand, whereas numbers of aboveground species are highest in the tropics.
Patterns were also similar for earthworm abundance (number of earthworms per are) and earthworm biomass (mass of earthworms per area). But while there are fewer earthworms in the tropics, the variation from location to location seems to be much higher. However, many tropical earthworm species have not been identified yet, so it’s still uncertain whether earthworms in one region are the same as those found in another.
Interestingly, they also found that climate is more important in shaping earthworm communities than properties of the soil itself. Precipitation and temperature have the largest influence on the number, abundance, and biomass of earthworms.
This means that climate change could have a significant impact on earthworm populations and on functions and ecosystem services they provide, explains Eisenhauer. And given their important role in soil ecosystems, this raises concerns about the “potential cascading effects on other organisms such as microbes, soil insects, and plants.”
Putting knowledge into action
Conservation efforts usually focus on aboveground biodiversity, whereas equally important belowground critters are easily forgotten. Therefore, biodiversity hotspots should be reassessed to include earthworms and protecting earthworms and other belowground species should be made a priority.
Climate change could affect the essential functions that earthworms and other soil organisms provide. And without earthworms, soil health and plant productivity are at stake.
(1) Phillips, H.R.P. et al. Global distribution of earthworm diversity. Science (2019). DOI: 10.1126/science.aax4851