One of the most pressing issues in modern ecology is the interaction of soil and terrestrial food webs. The former are detrital, that is, based on dead organic matter, while the latter are grazing, based on the green parts of plants. Direct trophic (food) links between terrestrial and underground communities are varied, but they are rarely taken into account in food web models. Earthworms are one such link: they live in the soil and feed on dead organic matter, but often leave their usual environment and crawl to the surface, where they become victims of a variety of terrestrial predators, from beetles to thrushes and badgers. This phenomenon is widely known, but quantitative data on how terrestrial predators affect earthworm populations are virtually nonexistent.
Fig.1 Attack rates on the model per day (means and 95% confidence intervals) for all predators combined, and for arthropods, birds, and mammals separately. Models were deployed either on soil (“worms”, blue diamonds) or on plants (“caterpillars”, red circles) in different ecosystems, from left to right: alpine tundra, mixed forest, and tropical monsoon forest in the dry and wet seasons. Different letters indicate statistically significant differences.
To study this issue, specialists from the Institute of Ecology and Evolution RAS conducted an experiment with plasticine models of worms and caterpillars. This approach has been used for a couple of decades to assess the predator load on herbivorous animals, but it has not yet been applied to soil communities. The essence of the method is simple: plasticine models resembling worms or caterpillars in shape and size are placed in model biotopes; various animals try to attack them and leave traces of their bites on the plasticine. The damage on the models clearly shows which predators (arthropods, reptiles, birds, mammals) tried to eat them.
The work used plasticine models of two types: "worms" on soil (a total of 2208 models) and "caterpillars" on vegetation (1668 models). The work was conducted in the monsoon forest of Vietnam (Cat Tien National Park), in a mixed forest in the Moscow region (the Malinki biological station of the IEE RAS), and in different variants of mountain tundra in the Khibiny Mountains (Murmansk Region, N.A. Avrorin PABSI). It turned out that in the forests of Vietnam and the Moscow region, arthropods most often attack the worm models, while in the Khibiny tundra, mammals do so. In almost all cases, predators attack the worm models more often than the caterpillar models. As expected, the highest level of attacks was recorded in Vietnam during the wet season.
The results of the study emphasize that underground resources can be important for maintaining terrestrial food webs, and even the simplest tools can help study this phenomenon.
The work was carried out within the framework of the RSF project No. 22-14-00363. The article was published in the journal Applied Soil Ecology: Vinogradov D. D., Sotnikov I. V., Tiunov A. V. (2024) Plasticine models confirm high predator pressure on surfaced earthworms in different ecosystems. Applied Soil Ecology, 202: 105594.
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