MODERN STATUS OF DIVERSITY OF SOIL MESOFAUNA COMMUNITIES IN MEADOW-STEPPE AREAS OF NORTHERN PODILLIA

© 2020 I. Y. Tsaryk et al.; Published by the Ivan Franko National University of Lviv on behalf of Біологічні Cтудії / Studia Biologica. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://www.budapestopenaccessinitiative.org and Creative Commons Attribution 4.0 License), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited. UDC: 504.53:592](477.8)


INTRODUCTION
The life cycle of soil invertebrates lasts for a long time in soil [9]. Almost all groups of invertebrates are associated with soil and are an important component of terrestrial ecosystems after autotrophic organisms. Soil invertebrates perform a variety of functions in ecosystems, in particular, they decompose dead plant remains, participate in the biotic cycle, assist in the formation of primary production and soil cover, regulate microclimate and water balance, serve as food for other organisms. [5,26,28]. At the same time, the diversity of soil invertebrates depends on the terrain, vegetation, seasonal hydrothermal conditions etc., and is variable. Depending on the influence of various ecological factors, some changes in the ratio of the prevalent and scanty species, groups of phytophages, zoophages, saprophages and polyphages take place. The intensity of these changes significantly depends on the biotope, its present and past states. The diversity of soil invertebrates is determined by the physical and chemical structure of soil, its aeration, temperature, as well as the presence of organic matter [1,21]. Soil is one of the most inhabited by species ecosystem components. In this study, we focus on the research of mesofauna communities of soil and ground litter of two meadow-steppe areas of Northern Podillia, where such investigations haven't been conducted before.
Soil invertebrates are usually divided into a number of functional groups; their disappearance can lead to irreversible consequences for the ecosystem [1]. According to the Lavelle classification [12], there are key groups of soil organisms, in particular "ecosystem engineers", which are the organisms that significantly influence the soil by mixing it, constructing aggregate structures, building underground passages, and are involved in the biotic matter circulation. Besides, there is one more group of "engineers" -chemical engineers and biological regulators. The former are presented mostly by microorganisms, bacteria, and fungi. The latter are mainly protozoans, nematodes, and microartropods that control the population density in food chains, as well as the availability of resources, which are under control of chemical engineers [1]. So, "ecosystem engineers" are the organisms that alter the environmental conditions of other organisms mechanically [11,13]. This group includes earthworms, termites, ants, isopods and rhizosphere. One of the aspects of our work is to emphasize the role of Formicidae in the structure of soil invertebrate complex on the sample sites, and to note that soil structures of Formicidae (ant-hills) may exist even after ants have left the area. The biomass of ants, in particular biotopes, can reach 15-25 % of the biomass of all organisms. Most of the ants are non-specialized zoophages and necrophages; some of them can grow fungi and other insects in their nests [27].
The aim of our research is to determine the current status of soil mesofauna diversity, structural and functional organization of their communities with reference to the taxonomic diversity and dynamic density of meadow-steppe areas of Northern Podillia, and to characterize the species diversity of ants as "ecosystem engineers". Such a comprehensive study in this area has been undertaken for the first time.

MATERIALS AND METHODS
The study was conducted in 2018 on two relic meadow-steppe sample sites of the Holohoro-Voroniatsky hills of Podillia. They are exposed to partial artificial afforestation associated with spontaneous sylvatization involving Pinus sylvestris and some shrubs, mainly Crataegus sp., Prunus spinosa, Rosa sp., Viburnum opulus, Sambucus nigra, Corylus avellana, etc.
Sample site 1. A meadow-steppe area located on the western gully slope under the summit of Makitra Mt. (15-20° steepness). The xeromesophilic meadow steppes communities of Cirsio-Brachypodion pinnati union with the fragments of Festuco-Stipion (Festuco-Brometea class) and forest-steppe plots of Geranion sanguinei union (Trifolio-Geranietea class) are present on sod-calcareous soils of the site [16]. Carex humilis, Festuca rupicola agg., Briza media, Elytrigia intermedia, rarely Brachypodium pinnatum and Stipa pennata dominate in the grass cover. According to the geobotanical zoning, this sample site belongs to Kremenets district of oak-hornbeam and oak-pine forests of Kremenets-Khotyn region of the East European province [2].
Sample site 2. A meadow-steppe area located on the second natural terrace of the western slope of Bila (Pidlyska) Mt. The xeromesophilic meadow steppes communities of Cirsio-Brachypodion pinnati union with the fragments of forest-steppe plots of Geranion sanguinei union (Trifolio-Geranietea class) are present on sod-calcareous soils. Carex humilis dominates in the grass cover, but, unlike the first sample site, Stipa pinnata is absent and such West Podillia endemics as Carlina onopordifolia and Chamaecytisus blockianus are present here. According to the geobotanical zoning, this sample site belongs to Holohoro-Voroniatsky district of beech forests of Kremenets-Khotyn region of the East European province [2].
The sampling and inventory of soil mesofauna was accomplished by means of Barber pitfall traps (standard glass containers (0.5 jars) dug into the soil at the surface level and filled up with 4 % formaldehyde solution on one third). 10 traps were positioned along the line every 10 m. The material was collected monthly from May to September.
Material analysis was carried out by standard methods [7,8,10]. The taxonomic composition of invertebrate communities was determined to species or higher systematic level (genus, family). Invertebrate species determination and analysis of their spatial distribution were based on a number of studies [3,4,6,14,15,18,19,22,24]. The ordering of animals into trophic groups was carried out according to B.R. Stryganova [23]. The dominance structure of invertebrate taxa was established after Tischler [25].
The indicators of taxonomic diversity (S), dynamic density (N, individuals per 100 trap-days) as well as dominance structure (%) of invertebrate soil fauna in the communities of relic meadow-steppe areas of Northern Podillia are presented in Table 1.
It was found out that mesofauna communities of the investigated sites 1 (Makitra Mt.) and 2 (Bila Mt.) being similar by taxonomic structure, differ by the dynamic density of some invertebrate groups (Table 1). Insects having the highest indicators of diversity (up to 60 %) and dynamic density (up to 80 %) dominate in the communities in general. Among the other taxa Oniscoidea and Diplopoda show high diversity too, being dominants and subdominants by dominance structure, while the rest of the taxa are recedents and subrecedents (Table 1).
In the structural and functional organization of the invertebrate communities (trophic groups), phytophages prevail by their diversity (39 taxa), and zoophages predominate by the dynamic density (up to 70 % of numbers in collected material) ( Table 2).  (Fabricius, 1793), Lasius plathythorax Seifert, 1991. We also detected Myrmica deplanata Emery, 1921, which is a steppe termophilic species typical of open biotopes with sparse grass vegetation (site 1), and Tapinoma erraticum (Latreille, 1798) that inhabits dry warm areas (site 1). Actually, the two latter species are the indicators of steppe areas [19].
Formicidae, being "ecosystem engineers" who alter the environment for other invertebrate groups of ground litter mesofauna by their activity, are eudominants (60-70 %) among the insects by the indicator of dynamic density.
Lumbricidae in our material are presented at the level of recedents and their part in total dynamic density does not exceed 1 % (0.1-0.6 %), which accounts for their coincidental representation in the traps.  Koch, 1847)). These are pan-European, Table 1.  Table 2. forest-steppe species also typical of broadleaf oak-hornbeam and pine forests on sandy soils; they are common meso-calciphils [17]. The dynamic density of Diplopoda is considerable and varies from 25 to 273 individuals per 100 trap-days ( Table 2). The dominance structure of other taxa reveals recedent and subrecedent levels (Tables 1 and 2). Blattodea, Ectobius sylvestris (Poda, 1761) in particular (max. 150 individuals per 100 trap-days), and Dermaptera (Forficula auricularia Linnaeus, 1758) (up to 40 individuals per 100 trap-days) are the most common representatives of saprophages. The rest of insects are presented mostly by imago and larvae of Silphidae (Necrophorus vespillo Linnaeus, 1758), while larvae of Diptera (Sciaridae, Tipulidae, Bibionidae (Bibio marci Linnnaeus (1758)) are sparse.

Таблиця 2. Трофічні групи мезофауни безхребетних лучно-степових ділянок Північного Поділля (S -різноманіття таксонів, N (%) -динамічна щільність)
Imago and larvae of Tenebrionidae (Pedinus femoralis L., 1767, Opatrum sabulosum L., 1761, Blaps halophila is less likely) have a considerable representation within the investigated communities. These bugs are typical steppe and desert inhabitants and phytopages by their trophic specialization. The presence of these species on the research sites testifies the value of their habitats within the refugia of meadow steppe vegetation of Northern Podillia.
7 Elateridae species were found in the invertebrate communities. We also identified 14 species of mollusks from 9 families. They are as follows:  (Ferussac, 1821)). These species are common for the lowland part of Western Ukraine, 70 % of them being steppe calciphils. Their typical habitats are open dry biotopes, warm slopes with low grass vegetation, and denudations of geological strata [24]. The rare species included in the Red Data Book of Ukraine is Granaria frumentum (Draparnaud, 1801) [20]. The dynamic density of terrestrial mollusks is low and doesn't exceed 5-6 individuals per 100 trap-days.
We suggest protecting the unique meadow-steppe areas of Northern Podillia from the consequences of the transformation processes caused by sylvatization as it might change soil mesofauna. The species whose distribution is not typical of this territory will be affected in the first place.