The aim of our study was to determine the current distribution, habitats, ecology, and possible dispersal routes of three species of the Rudny Altai (East Kazakhstan): Eisenia tracta, E. nana, and E. ventripapillata. We found that these species dispersed far beyond their original distribution into the flatland part of western Siberia (Russia) up to the central forest steppe of the Omsk oblast. E. tracta, E. nana, and E. ventripapillata were found in both floodplains and interfluvials. Hydrochory was the most plausible way of northward dispersal, while on interfluvials, they were probably introduced by humans. The studied species showed no preference for a particular habitat or river bank. The habitats were diverse and significantly different from the original ones in Rudny Altai. The factors that allowed E. tracta, E. nana, and E. ventripapillata to colonize western Siberia were probably their wide tolerance range to soil pH, temperature, density, and humidity, along with the decrease of winter soil freezing in recent decades. This is the first information about the occurrence of these species of earthworms in Siberia.

Most soils possess a large supply of nutrients, but these reserves cannot be mobilized by plants, as they exist in a bound form. Therefore, it is need to understand mechanisms that naturally increase the acquisition of nutrients by plants. Earthworms are crucial soil engineers that play a key role in soil functioning. In this study we have estimated the impact of three factors, earthworm species, ecological group, and soil type, on the ion content of casts of Eisenia nordenskioldi, E. ventripapillata, E. nana, Lumbricus rubellus, and Aporrectodea caliginosa. Laboratory experiments were performed in microcosms on three soil types. We analyzed five water-soluble cations and six anions in the earthworm casts by capillary zone electrophoresis to determine their content in casts compared to soil. For three of the five species studied this is the first information obtained on the matter. The obtained data demonstrated that soil type has the biggest impact on the observed changes in the cast ion content, probably due to the differences in the initial concentrations and soil properties. Within each soil type, the observed effects were mostly species-specific, and the species belonging to the same ecological group (endogeic and epi-endogeic) did not have similar effects. The exposure to different earthworm species resulted in pronounced differences in the concentrations of magnesium, calcium, ammonium, and chloride, while the soil type had the highest impact on sulfate, fluoride, acetate, and sodium ions. Therefore, the terms ‘ecological group’ and ‘functional group’ are not equivalent for earthworm casts, and replacing an earthworm species with another belonging to the same ecological group may result in changes of the soil ion composition.

According to the results of 9 years of earthworm collections in soil in Omsk oblast from 2009 to 2018, their population has been analyzed in order to identify the main environmental factors associated with the territorial heterogeneity of species richness and group density. Five types of Lumbricidae populations have been identified, two of which are divided into two subtypes, where ten species and two subspecies of earthworms are found. It has been established that environmental factors such as zonality and subzonality; the depth of the soil layer; and, to a lesser extent, the topography characteristics have the greatest influence on the distribution of worms: 9, 7, and 0.7% of the considered variance of the density similarity matrix, respectively. In general, all environmental factors and their combinations (modes) explain 38% of the considered variance; the multiple correlation coefficient is 0.62. Dendrobaena octaedra (7–52%) and Aporrectodea caliginosa (15–74%), alien species of European origin, and the native Eisenia n. nordenskioldi (6–28%) took over in terms of the share of the population density in most taxa of the classification, as well as Eisenia ventripapillata (42%) and E. nana (16%) of Asian origin, for the territories of the southern forest steppe and steppe. Such changes in earthworm populations, namely the replacement of native species of the Eisenia nordenskioldi complex with alien species, can significantly affect soil characteristics and ecosystem services determined by earthworms.

Earthworm invasions often reduce biodiversity and affect the ability of ecosystems to perform ecosystem functions. Over the past few decades, European lumbricid species have spread widely in natural habitats in Western Siberia, without completely displacing the native species. The aim of the present experiment is to study the survival, reproductive potential, vertical distribution, abundance, and biomass of Aporrectodea caliginosa and Lumbricus rubellus invasive species for the region and the native species Eisenia nordenskioldi and their influence on each other. For this purpose, winter and vegetation experiments were conducted in mesocosms simulating the real situation of invasions in the same communities on the same types of soils with the same amount and composition of litter. The authors found that the native species was significantly inferior to A. caliginosa in reproduction rate, number of offspring, and final biomass, but had an advantage over L. rubellus. The native species was positively influenced by the presence of A. caliginosa. In the experiment, there was a significant rejuvenation of the populations of the studied species, as well as an increase in abundance and relative mass under interaction conditions compared to mono variants. The native species had advantages over the invasive species in terms of winter survival. The natural volume of litter used in the experiment was insufficient for L. rubellus. According to the results of the experiment, it can be assumed that the spread of L. rubellus will continue to be limited to non-freezing biotopes rich in organic matter. A. caliginosa will spread in natural communities and agrocenoses of Western Siberia.