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Analysis, published in Nature ecology and evolution Led by Stanford and Sorbonne universities, it provides the largest database ever created on this type of worm and warns of the need to better understand and manage the invaders among us.
“Earthworms tell the story of the Anthropocene, the era in which we live“It's the story of the global homogenization of biodiversity by humans, which This often leads to the decline of unique local species and to change local ecosystem processes.
Often unseen and unappreciated, Earthworms are worth their weight in gold to farmers and gardeners Because their movement creates tunnels that allow air, water and nutrients to pass through, while their waste acts as a rich fertilizer. They also play a central role in many processes that affect surface communities and the atmosphere. For example, although the mechanical movement of worms through the soil may initially release carbon dioxide, the long-term effects of digesting organic matter Leads to a net increase in sequestered carbon Where worms are found.
Since the late 1800s, people seeking to take advantage of these services have brought earthworms to North America from Asia, Europe, South America, and Africa. In some places, these non-local introductions have improved the agricultural economy. However, in other cases it is harmful. These plant transplants are more likely to consume aerial leaf litter than native earthworms, altering habitat quality in a way that could harm native plants, amphibians and insects.
In the broadleaf forests of the northern United States and Canada, The impact of alien earthworms on soil stresses trees such as sugar maples by changing soil microhabitats. This, in turn, leads to a cascade of effects on the food web that help invasive plants spread. Ironically, for a creature synonymous with soil improvement, some exotic earthworms can alter soil properties, e.g Nutrients, pH and textureThis leads to reduced crop quality, among other effects.
the Exotic worms They have a clear advantage. Unlike most of our native species, many female species of exotic worms can produce offspring without fertilization by a male. next to, Climate change opens new areas for colonization in the northern regions of the continent, Where permafrost is melting and where there are no native earthworms.
Despite all this, only a limited number of studies have documented the spread of exotic worms None of them covered the dynamics of colonialism On a large spatial scale or a large number of species.
In their study, the researchers relied on thousands of records from 1891 to 2021 to create a database of domestic and exotic earthworms, then combined it with a second database documenting interceptions of exotic earthworms on the US border between 1945 and 1975. For machine learning, the team used the combined databases to reconstruct hypothesized pathways for the introduction and spread of alien earthworm species.
They found alien species of earthworms in 97% of the soil studied in North America, with alien occupation greater in the northern part of the continent and less in the south and west. Overall, exotic species represent 23% of the continent's 308 earthworm species, and represent 12 of the 13 most widespread earthworm species. In comparison, only 8% of fish species in the United States, 6% of mammal species, and 2% of insects and spiders are exotic.
In Canada, the proportion of exotic worms is three times that of native worms. In most of the lower 48 states and Mexico, there is approximately one exotic worm for every two native species.
“These proportions are likely to increase as human activities facilitate the evolution of alien species that threaten native earthworm species.“It's a phenomenon that is still largely ignored,” said the study's lead author, Jerome Mathieu, an associate professor of ecology at the Sorbonne who conducted the research while a visiting professor at the Hadley Lab.
Not all exotic worms will threaten local ecosystems. However, according to the researchers, their widespread distribution and little-known impact on a variety of local ecosystems, such as grasslands and conifer forests, means they deserve close attention. Among other solutions, they suggest that policymakers focus on prevention, such as encouraging the use of native worms for composting and fishing bait, and early detection through regular monitoring and citizen science.
