European earthworms reduce insect populations in North American forests

European earthworms that have entered northern North America have a negative effect on the aboveground insect fauna.

Soil ecologists, led by the German Center for Integrative Biodiversity Research (iDiv) and the University of Leipzig, describe this observation in the journal Biology Letters.

The researchers found this effect on the abundance as well as the biomass and species richness of insects. Their findings suggest that changes in insect communities may have causes that have not received much attention before. writes that they should be given more attention when it comes to nature conservation.

European earthworms arrived in America in plant transfers

At least since the last Ice Age, about 10,000 years ago, there have been almost no worms in the northern part of North America. However, over the past few centuries, it has been introduced, probably through soil and plant transfers into Europe.

Since then, they have dispersed and changed the soil dramatically, with far-reaching consequences for the ecosystem. The impact of European earthworms on the world above ground has rarely been investigated.

The study was conducted in a forest near Calgary, Canada, which has areas either inhabited or uninhabited by earthworms. Here, researchers used vacuum tubes to capture above-ground insects and compare catches.

They found that insect abundance, biomass, and species richness in areas with invasive earthworms differed significantly from those in areas without earthworms. Where earthworm biomass was the highest, insect population decreased by 61%, insect biomass by 27%, and species richness by 18%.

Insects on the surface are affected by earthworms below

“We expected earthworms to have an effect on above-ground insects. But even so, I was surprised by how pronounced the effects were, not only species abundance, but also biomass and species richness,” says Dr.

However, the mechanisms by which earthworms affect insects remain unclear. “Earthworms may eat the food and reduce the habitat of those above-ground insects, such as beetles and fly larvae, that break down dead plant material,” says Yochum.

Since most insects are herbivores, it can also be assumed that the observed decrease in insects is due to changes in vegetation cover, due to changing soil conditions.

However, in this case, the researchers were unable to detect any significant change in the number of plant species or vegetation cover. “However, this does not rule out the influence of plants,” Yochum says. Data on species composition and other functional characteristics of plant communities have not yet been evaluated.

The growth of insect species and predatory spiders was also amazing. They seem to be benefiting from the changes.

Underestimated causes of biodiversity loss must be taken into account when conserving

“So far, only a few reasons have been used to explain global changes in insect numbers. Especially changes in aboveground habitats,” says Professor Nico Eisenhower, from iDiv and the University of Leipzig.

“These new findings show that biodiversity loss may have other causes that have not received much attention to date, and that they must be taken into account when developing biodiversity management and conservation strategies,” says Eisenhower.

Introduced European earthworms are found not only in North America, but on almost every continent. However, since there have been very few earthworms in northern North America for a very long time, the influence of these invaders is especially evident.

“For regions like Europe, where natural communities have always evolved alongside earthworms, similar negative effects due to new earthworm species are highly unlikely. Instead, there are important factors of ecosystems here, on which many of their important functions depend.” , says Gotchum.

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