‘Immigrant worms’ evicted 61% of arthropods from Canadian forests

(ORDO NEWS) — Earthworms, as a rule, are considered perhaps the most useful creatures for all inhabitants of the biocenosis, in which there are rings.

But since the last ice age, there have been no earthworms in North America, and the local ecosystem has developed just fine without them.

But in the process of developing North America, the Europeans brought with them “soil immigrants”. Which also began to conquer the hitherto unknown frontier for them and, as it turned out, cause serious damage to biodiversity.

The mechanisms of this process are not yet fully understood, since the number of not only those animals with which the worms compete for food is decreasing.

During the preparation of their work, German scientists found that in the studied areas of the Canadian forest, “immigrants” led to the following effects: the total number of arthropods decreased by 61%; 18% of species disappeared; the total biomass of arthropods decreased by 27%.

An article describing the study and detailed findings was published in the Biology Letters of the Royal Society of London.

It was prepared by the staff of the German Center for the Integrated Study of Biodiversity ( iDiv ), as well as the Universities of Calgary, Göttingen and Leipzig.

They analyzed the number, mass and species diversity of arthropods at 60 sites in a deciduous forest on the shores of Lake Barrier in the Canadian province of Alberta.

The sampling sites were determined as follows. Scientists first chose the most sensitive to the presence of earthworms biocenoses.

Then, the current presence of these invasive protostomes in them was clarified and the studied areas were divided into three groups. It turned out 20 places for sampling material – with low, medium and high “content” of worms in the soil.

Immigrant worms evicted 61 of arthropods from Canadian forests 2Summary of counts of all invertebrates at sampling sites. Graph columns from left to right: all arthropods, herbivores, omnivores, carnivores, detritivores, parasitoids. Rows of graphs from top to bottom: number of arthropods per square centimeter, total fresh weight of collected animals (in milligrams per square centimeter) and species diversity. In places where the soil contains a lot of worms, the surface also had an increased number of not only predators, but also parasitoids

A total of 13,037 invertebrates were collected, sorted, identified and classified according to their role in the food chain.

Of these, 230 are snails, the rest are arthropods, including hemipterans, dipterans, hymenoptera and vesicles, as well as spiders.

The inhabitants of the surface were caught by a specially equipped vacuum cleaner, those that were hiding in the ground – manually or by driving out of it with a special composition with mustard.

After all the calculations, the researchers compared the biodiversity at different sampling sites. And they were very surprised by the influence of earthworms on the surface ecosystem.

Moreover, other factors that would reduce the number and “range” of insects could not be found. Interestingly, against the background of a general decline in biodiversity, in places where there are a lot of worms, predatory arthropods, mainly spiders, have also increased.

It is also not possible to explain this phenomenon yet, spiders do not feed on worms (with extremely rare exceptions).

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