Oct. 25 (UPI) -- Most biodiversity hot spots are found in the tropics, but according to a new study, earthworm diversity is actually greatest in temperate soils.
Because of the many ecological services they provide, including decomposition and nutrient cycling, earthworms are considered "ecosystem engineers." Within many ecosystems, earthworm biomass is actually greater than the biomass of all resident mammals.
But while much is known about the ecological services provided by earthworms, from carbon sequestration to seed dispersal, less is known about their global distribution.
To address this knowledge gap, an international team of scientists spearheaded a massive earthworm survey, collecting samples of earthworm communities from 6,928 sites in 57 countries.
Researchers used the new earthworm dataset to build a map of earthworm distribution and identify global patterns in earthworm diversity, abundance and biomass.
"Initially, we thought this is a crazy idea. But then, we were impressed how many colleagues were highly motivated to share their data for this exciting endeavor," Nico Eisenhauer, head of the experimental interaction ecology research group at Leipzig University, said in a news release. "We basically started from scratch in 2016 -- only a couple of years later we could publish one of the largest datasets on soil biodiversity. This is an amazing achievement of the lead author Helen Phillips and the many scientists that trusted in us."
The dataset and related map, published this week in the journal Science, showed earthworm communities are more diverse in the temperate regions than in the tropics. Analysis provides that temperate ecosystems also host a greater earthworm abundance and biomass. The range of earthworm communities in the tropics is limited, researchers reported.
"In the tropics, if you drive just a few kilometers, you may find a whole new set of earthworm species, while in the colder regions they remain more or less the same," said lead study author Helen Phillips. "This could mean that while there are few species found in a single location in the tropics, the total number of species across the whole region may in fact be extremely high. But we don't know yet."
When scientists looked at the relationship between earthworm communities and environmental conditions, they found strong precipitation and temperature had the greatest affect on the makeup and biomass of earthworm communities.
"Based on these strong climate effects, we conclude that climate change could cause shifts in earthworm communities and change the functions and services ecosystems provide," said Eisenhauer. "Given their role as ecosystem engineers, we are concerned about potential cascading effects on other organisms like microbes, soil insects and plants."
As scientists and conservationists begin to prioritize biodiversity and the comprehensive health of intact ecosystems, as opposed to single species, the authors of the latest study hope policy makers will consider the importance of the biodiversity found in the soil.
"Earthworms may be cryptic and may not have the charisma of a panda bear, but they are extremely important for other organisms and the functioning of our ecosystems," Eisenhauer said.