Arachnids (Araneae, Opiliones) from grass stand and forest litter in the Urals, Russia

Abstract Background Since the late 1980s, long-term monitoring of various components of natural ecosystems under conditions of industrial pollution has been carried out in the Central Urals. In the mid-2000s, similar programmes were started in the Southern Urals. As a part of these monitoring programmes, the data on invertebrates in different types of biotopes, collected with different methods and in a different time intervals, continue to be gathered. Amongst the most well-studied groups of invertebrates are spiders and harvestmen whose communities are a convenient indicator of the environment. The data collected through these monitoring programmes can also be used to study natural local biodiversity. New information The dataset, presented here, includes information from a long-term monitoring programme for Araneae and Opiliones that inhabit grass stands of secondary dry meadows and litter of spruce-fir, aspen-birch and pine-birch forests in the Central and Southern Urals. The dataset (available from the GBIF network at https://www.gbif.org/dataset/e170dbd1-a67f-4514-841c-5296b290ca90) describes the assemblage structure of spiders and harvestmen (list of species and their abundance), age-sex composition and seasonal and inter-annual dynamics for two large areas in the southern taiga zone of the Ural Mountains. The dataset includes 1,351 samples, which correspond to 5,462 occurrences identified during 2004–2009, 2013 and 2018. In total, we collected 10,433 specimens, representing 178 species (36% of arachnofauna of the Urals), 115 genera (54%) and 23 families (100%). Most of the data (4,939 of 5,462 occurrences, 90%) were collected in the western macro-slope of the Ural Mountains (European part of Russia), the rest in the eastern macro-slope (Asian part). All represented data were sampled in industrially undisturbed areas and are used as a local reference for ecotoxicological monitoring. The dataset provides new useful information for recording the state of biodiversity for the Central and Southern Urals and contributes to the study of biodiversity conservation.


Introduction
The arachnids are a widespread group of invertebrates; almost all Araneae and many Opiliones are obligate predators. It was shown that spiders can be used as indicators of local diversity (Willett 2001). All parameters (abundance, diversity, evenness and species richness) of arachnid communities demonstrate a close relationship with the structure of their habitats (Rubio et al. 2008). This makes arachnids a good tool for assessing the components of diversity on a local spatial scale (Rodriguez-Artigas et al. 2016).
The fauna of spiders and harvestmen in the Central and Southern Urals is currently one of the most studied in Russia. At the present time, the fauna of Araneae of the Urals includes 485 species belonging to 202 genera from 23 families (Esyunin 2015) and the fauna of Opiliones includes 10 species from 10 genera of two families (Farzalieva and Esyunin 1999). Local diversity ratings of the fauna are lower for Araneae: there are 235 species and 127 genera for the Central Urals and 180 species and 112 genera for the Southern Urals (Esyunin 2015). For Opiliones, local diversity is almost no different from the regional: there are 10 species and 10 genera in the Central Urals and eight species and eight genera in the Southern Urals (Farzalieva and Esyunin 1999). The first special work devoted to the fauna of the spiders of the Urals contained information on 86 species collected mainly in the vicinity of Yekaterinburg (Kharitonov 1923). Subsequently, this same researcher published a catalogue with more than 200 species of spiders recorded for the Urals and Cisurals (Kharitonov 1932, Kharitonov 1936. In the second half of the twentieth century, intensive multi-year studies were carried out for various territories of the Central (Azheganova and Glukhov 1981, Esyunin 1991, Pakhorukov et al. 1995 and Southern (Olshvang and Malozyomov 1987, Polyanin and Pakhorukov 1988, Esyunin and Polyanin 1990 Urals. As a result of this work, a catalogue was published with a summary of all the information available at that time on the fauna of the spiders of the Urals and Cisurals (Esyunin and Efimik 1996). The global fauna of harvestmen was poorly studied until the end of the 1970s, when the number of studies began to gradually increase (Kury 2012). Harvestmen fauna of the USSR includes 74 species in the mid-1930s (Redikortsev 1936) and 110 species in the late 1970s (Staręga 1978). The last paper presents the first data on the species composition of harvestmen in the Urals region (specified as a part of Western Siberia). By this time, the fauna of the European part of the USSR (58 species) has been the most well-studied (Chevrizov 1979). A comprehensive review of harvestmen of the Urals (10 species) is given later in the catalogue of local fauna (Farzalieva and Esyunin 1999).
The presented dataset for the Central Urals contains 166 species (of which 159 species (68% of total regional fauna) are spiders and seven (70%) are harvestmen) and for the Southern Urals, it contains 55 species (53 (29%) and two (25%), respectively). Poor level of knowledge of the fauna of the Southern Urals is caused by the limited extent of monitoring (currently only one year). The family with the greatest number of species and genera is Linyphiidae (50% and 56%, respectively). In the temperate climatic part of the Urals, local arachnid fauna are comparable in terms of the ratio of families with the largest number of species (Esyunin 2015).
Spider fauna of the Urals has a number of distinctive features. Firstly, it can be characterised as poor: the diversity is lower than that of the fauna of the adjacent plains (both East European and West Siberian (Esyunin 2015)), as well as of the neighbouring mountainous countries. For example, 1110 species are known for the arachnofauna of the Caucasus (Otto 2019) and 614 species for the Republic of Tyva, South Siberia (Marusik et al. 2000). Secondly, the fauna has an extremely low endemicity. This, along with a low diversity, indicates the allochthonous character of the Ural fauna of spiders and the young age of its modern composition (Esyunin 2015).

Study extent:
The study was conducted in the southern taiga zone of the Central and Southern Urals, Russia, in the lowest part of the uplands (300-400 m above sea level). A total of twelve sampling plots (= locationID) were established across three types of biotopes: primary spruce-fir (four plots), secondary aspen-birch forests (two plots), pinebirch forest (three plots) and secondary upland meadows (three plots). Sampling description: Sampling of meadow grass stand invertebrates was completed using a biocenometer. Samples were collected at three permanent free-form sampling plots (approximately 2500 m in size) that were positioned at a distance of 100-300 m from each other in the lower parts of the secondary upland meadows created through forest clear-cutting more than 60 years ago (Table 1). Sampling effort (time interval for collecting 2 Figure 1. Location of the sampling plots in the Central and the Southern Urals (data from SASPlanet). one sample) was approximately 25 minutes. All samples were collected no closer than 10 m from the forest edge. The points for installing the biocenometer were chosen randomly, but at intervals of no less than 5 m. The sampling procedure was carried out from 09:00 to 21:00 h local time. The sampling plots were examined on the same day. Morning-, middayand evening-time-collected samples were available for each investigated plot. Sampling was timed to the second half of every summer month ( Sampling was performed by using a modified biocenometer consisting of a bottom (metal frame 50×50 cm) hermetically connected to a cube-shaped covering of a dense cloth (Fig.  2). One of the lateral sides of covering was sewn from nylon gauze (mesh diameter 0.25 mm) and used as a light screen to attract invertebrates with positive photokinesis. The opposite-to-screen side of the covering contains an aperture with an inlet valve for the researcher. Invertebrates were collected with a suction sampler from a light screen and inner surfaces of the biocenometer until the new targets stopped appearing. All the plants that got inside were also processed with a suction sampler (to gather invertebrates), cut with scissors at ground level and taken away for a manual check for hidden invertebrates.
Then the biocenometer was turned over and its inner surface and seams were examined, as well as the soil surface and bases of the plant stems. All detected invertebrates were devitalised by ethyl acetate and preserved in 70% alcohol. Appearance of the biocenometer (A) and a circuit of an original sampling header (B) (1detachable part of the bottle, 2 -longitudinal cuts, 3 -perpendicular cut, 4 -membrane of nylon gauze, 5 -air intake pipe) Pitfall trapping was carried out in biotopes most typical for the studied areas: primary spruce-fir forest, secondary aspen-birch forest and pine-birch forest (Fig. 3). Sampling plots were founded in sites with the lowest degree of degradation of woody vegetation ( Table 1). Sampling of forest litter invertebrates was conducted with two general schemes. The line-designed scheme (used for regular periodic accounting of forest litter invertebrates) includes five pitfall traps per trapping line, with a spacing of 3 m and three lines per sampling plot no closer than 100 m from each other (a total of eight plots, each approximately 2,400 m² in size) were examined both in spruce-fir (three plots) and aspenbirch (five plots) forests. The matrix-designed scheme (used to study spatial heterogeneity of forest litter invertebrates in different years) includes a 7×7 matrix of pitfall traps with 10 m spacing on a single square-form sampling plot (3,600 m²) in a spruce-fir forest. Pitfall traps of the same type (plastic glasses, diameter 8.5 cm, 3% acetic acid solution as a fixative) were used in both schemes. All plots and locations of every trap were permanent throughout the study. Sampling was conducted in twotime-sets; May-June and August-September (which is timed to the peak abundance of spring-summer and summer-autumn species) in 2004, 2009 and 2013 (for line-designed trapping) and in 2005 and 2018 (for matrix-designed trapping). The traps were emptied once per 3 to 6 days; all collected invertebrates were preserved in 70% alcohol.
Quality control: A total of more than 10400 individuals of spiders and harvestmen were collected. All specimens were wet-preserved in 70% alcohol and stored in the depository of the Laboratory for Population and Community Ecotoxicology of the Institute of Plant and Animal Ecology, Ural Branch, Russian Academy of Sciences (IPAE UB RAS). Most of the adult specimens were identified to species (except for those severely damaged during the sampling). Species identification was also carried out on juvenile specimens when there was no doubt about their identity. Identification of species was performed by a permanent team of researchers (IPAE UB RAS) using Nentwig et al. 2019 for spiders and identification keys of Farzalieva and Esyunin 1999 for harvestmen, as well as some additional monographs (Chevrizov 1979). Identification quality was cross-checked by Professor   (Farzalieva and Esyunin 1999).

Geographic coverage
Description: The studied areas are located in the southern taiga zone of the Central and Southern Urals. The polygon at the Central Urals is located 60-70 km westbound from Yekaterinburg in primary spruce-fir and secondary aspen-birch forests with secondary upland meadows created through clear-cutting. At the Southern Urals, two polygons are located 10 and 60 km NE from Miass, in pine-birch forest. The dataset describes the quantitative and qualitative structure of arachnids, age-sex composition and seasonal and inter-annual dynamics for two large areas in the southern taiga zone of the Ural mountains. Arachnids were sampled with three general schemes, which allowed the coverage of a wide range of habitats: inhabitants of grass stand were collected using biocenometer (three sampling plots (= locationID) in total), inhabitants of forest litter were collected using line-designed (eight plots) and matrix-designed pitfall trapping (one plot). The dataset includes 1351 samples (= sampling events), which corresponded to 5462 occurrences identified during 2004-2009, 2013 and 2018. In total, we collected 10433 specimens, representing 178 species (36% of arachnofauna of the Urals), 115 genera (54%) and 23 families (100%). Only samples that contained arachnids (occurrenceStatus = present) have been provided. The dataset represents the new data useful for recording the state of biodiversity of a region and contributes to the study of biodiversity conservation.

Column label Column description
eventID An identifier for the set of information associated with an Event (something that occurs at a place and time). May be a global unique identifier or an identifier specific to the dataset.
occurrenceID An identifier for the Occurrence (as opposed to a particular digital record of the occurrence). basisOfRecord The specific nature of the data record. specificEpithet The name of the first or species epithet of the scientificName. organismQuantity A number or enumeration value for the quantity of organisms. organismQuantityType The type of quantification system used for the quantity of organisms. scientificName The full scientific name, with authorship and date information, if known. kingdom The full scientific name of the kingdom in which the taxon is classified. phylum The full scientific name of the phylum or division in which the taxon is classified. class The full scientific name of the class in which the taxon is classified. order The full scientific name of the order in which the taxon is classified. family The full scientific name of the family in which the taxon is classified. genus The full scientific name of the genus in which the taxon is classified. taxonRank The taxonomic rank of the most specific name in the scientificName. locationID An identifier for the set of location information (data associated with dcterms:Location). decimalLatitude The geographic latitude (in decimal degrees, using the spatial reference system given in geodeticDatum) of the geographic centre of a Location. decimalLongitude The geographic longitude (in decimal degrees, using the spatial reference system given in geodeticDatum) of the geographic centre of a Location.
geodeticDatum The ellipsoid, geodetic datum or spatial reference system (SRS) upon which the geographic coordinates given in decimalLatitude and decimalLongitude are based.
coordinateUncertaintyInMetres The horizontal distance (in metres) from the given decimalLatitude and decimalLongitude describing the smallest circle containing the whole of the Location. Leave the value empty if the uncertainty is unknown, cannot be estimated or is not applicable (because there are no coordinates). Zero is not a valid value for this term.

ownerInstitutionCode
The name (or acronym) in use by the institution having ownership of the object(s) or information referred to in the record.
In the Southern Urals, sampling was carried out only in the prevailing biotope, the pinebirch forest litter (760 spiders and 14 harvestmen). A total of 16 families were revealed; greatest abundance and species richness were found in Lycosidae (40% of specimens, 11% of species), Linyphiidae (28% and 51%) and Thomisidae (13% and 7%). The family with the greatest number of species and genera is Linyphiidae, which is typical for arachnofauna of the climatically-temperate part of the Urals (Esyunin 2015).
It is interesting that the family Oxyopidae is represented only by juvenile specimens of Oxyopes ramosus (Martini & Goeze, 1778) ( Table 2). This is a xerophilous species, preferring open biotopes; in high latitudes, it is found in clearings, meadows and in the mountain-tundra belt. Based on our observations, adult individuals of this species are found mainly in shrubs (tamnobiontous); in the grass stand, these spiders are few and immature individuals are prevailing. Perhaps this is due to the peculiarities of the population structure at the northern boundary of the distribution of the species.
Age-sex composition is an important characteristic of the state of natural communities. For spiders, adult individuals predominate (Table 3), which is apparently related to the periodisation of pitfall trapping, attributed specifically to the peaks of abundance of the Schaefer 1987). However, this tendency manifests itself only for the meadow grass stand communities, while the forest litter is featured with the prevalence of males (Table 3). The reason, apparently, is the difference in sampling methods. For meadows, we used a biocenometer that provides a relatively complete registration of invertebrates; this allowed us to reveal the most typical ratio of sexes (Huhta 1965, Schaefer 1987. Communities of the forest litter were studied using pitfall traps, which allow recording the activity density. In some species of arachnids, males are more active (Topping and Sunderland 1992), which explains the higher abundance values. In addition, some species of spiders are more able than others to get out of traps (Topping 1993); perhaps this can also affect the numbers of male and female spiders caught.
Amongst the interesting finds of species, it is important to point out Sintula corniger (Blackwall, 1856) of Linyphiidae. This is a rare (widely distributed, but not numerous everywhere) species with a trans-European nemoral distribution area (from Great Britain and France to the Urals, from Fennoscandia to Romania and Azerbaijan (Nentwig et al. 2019, World Spider Catalogue 2020)). The Ural mountain range is the easternmost distribution boundary of this species, due to the north-eastern limit of distribution of the nemoral flora. The species was found in an aspen-birch forest, where an element of nemoral flora (small-leaved linden, Tilia cordata) is present in the understorey. Two adult male specimens were caught in pitfall traps in May 2004. This is the first find of this species in the Central Urals.