DOI: 10.5061/dryad.dr7sqvb76
title: Data from: The role of wild bees and cavity-nesting wasps as ecological indicators of the last traditionally managed meadows in Eastern Europe

description: The number of wild bees and cavity-nesting wasps is abundant in
 agricultural areas and they contribute significantly to ecosystem
 services. Due to their specialization in nesting sites
 and  food sources, these groups are sensitive to habitat
 condition changes and they are therefore important indicators for
 environmental impact assessments. As semi-natural habitats are steadily
 declining and often understudied, their significance for research is
 increasingly recognized. During this research, the role of wild bee
 species and cavity-nesting Hymenopteran taxa as indicators was examined,
 along the unique combination of high nature value and traditional land use
 habitats in Central Europe, Transylvania. Transects and trap nests were
 used to test the diversity and abundance of wild bees and cavity-nesting
 Hymenopterans in order to identify possible differences between highly
 protected and less protected areas. The differences in taxonomic groups
 between the sites and the potential effects of landscape structure on wild
 bees and cavity-nesting Hymenopterans were also assessed. We detected a
 high diversity of wild bee species and a significant species replacement
 from one study year to another. Among the nest-building Hymenopteran taxa,
 the majority of nests was built by Trypoxylon sp. during both study years,
 with a stronger dominance in the second year. The different taxonomic
 groups of wild bees and cavity-nesting Hymenopterans showed differences in
 their habitat affinities. The majority of the sampled bumblebee species as
 well as Trypoxylon sp. had an affinity towards the study sites located
 within the highly protected study area. Altogether, we found different
 habitat preferences for different Hymenpteran groups (both wild bees and
 wasps) and conclude that these groups definitely have the potential to
 serve as indicators for differences in the intensity of land use.
 cavity-nesting bees, solitary bees, wild bees, landscape structure, spider
 prey preference.
description: <strong>Study sites</strong> Our
 research was carried out in Transylvania (Romania) between 2018 and 2019
 in areas with traditional cultivation, extensive farming and high nature
 value. These areas rich in trees and shrubs have a high plant diversity
 and density. All study areas were located on the border of the counties of
 Hargita and Kovászna in a hilly-mountainous landscape, where the average
 altitude is 580m. These areas are mainly used as mowing fields. Mosaic
 plots rarely exceed one hectare in size and are relatively far from
 villages. The mosaic plots are mowed at different times of the year,
 providing a continuous source of food for pollinators throughout the year.
 The majority of the study sites was located in the Vargyas valley, which
 is part of the Natura 2000 network. The importance of these high nature
 value areas has recently increased due to the intensification of
 agriculture. There were three study areas, which were located within or in
 close proximity to Natura 2000 sites (Figures 1a and 1b): The
 Kormos-valley ('K'; Natura 2000 site ROSCI0091), the northern
 Vargyas-valley ('NV'; Natura 2000 site ROSPA0027), and the
 southern Vargyas-valley ('SV'; Natura 2000 site ROSCI0036). The
 Kormos-valley was the study area closest to human settlements, with small
 forest patches and a low number of arable fields in addition to extensive
 meadows. The study area in the northern Vargyas-valley was located at a
 medium distance from human settlements compared to the other two study
 areas and is mainly used as mowed pastures, grazed in early spring and
 late autumn. The nature reserve in the southern Vargyas-valley was located
 furthest from human settlements and is characterized by forests and mowed
 areas rich in trees and shrubs. <strong>Sampling
 of wild bees along a transect</strong> The study
 was conducted over two years (2018 and 2019), with sampling carried out
 once in May, twice in June, and once in July using the transect method. In
 each study area, three sampling sites were randomly assigned. Three pairs
 of transects of ca. 200m in length were assigned at the sampling sites,
 where two persons sampled simultaneously (Figure 1c). A distance of ca. 50
 m was left between the two transects and the transects did not cross. In
 all cases, sampling took place between 9 and 17 h, in sunny and calm
 weather, above 13°C and below 32°C. There was a considerable difference in
 the temperatures measured during May between the two years (3.7° C; Figure
 2a), while the precipitation was very similar (Figure 2b). During
 sampling, field-identifiable individuals (e.g. honeybee, some bumblebee
 species) were recorded, and those that could not be identified with
 certainty were placed in 70% alcohol. The wild bees collected were stored
 in alcohol and sent to taxonomic expert, Zsolt Józan for identification at
 the end of each year. <strong>Sampling of
 cavity-nesting Hymenopterans with trap nests</strong>
 To record the cavity-nesting Hymenopteran taxa in the three study
 areas (K, NV and SV), we set up eight study sites in 2018 (the study site
 NV2 was not sampled in this year) and nine study sites in 2019. Four trap
 nests in 2018 and three trap nests in 2019 per study site were deployed in
 2018 and 2019 (see also Lajos et al., 2021 and Lajos 2022). The trap nests
 were PVC pipes of ca. 12 cm in diameter and 23 cm in length filled with
 common reed (Phragmites australis), which were installed in May in both
 years. The reed was cut with a circular saw to a length of 22 cm, ensuring
 that each reed contained a node. The trap nests were placed 1.5-2 m above
 ground on nearby shrubs. The trap nests were collected in early September
 in both years and then stored in a cold shaded outdoor place until January
 - February. As the weather warmed, the trap nests were taken from this
 outdoor place and put into a refrigerator at 4-7°C. At the same time, we
 started processing the trap nests and recording data. We counted the
 number of reed stems in the trap nests and then cut each reed stem taking
 care of the nests inside. Where nests were found they were marked with a
 unique identification code. The following parameters were recorded for
 each reed: 1) diameter of the reed, 2) number of nest cells, 3) type of
 nesting material, 4) colour of larvae or cocoons, 5) type of food found in
 the brood, whether nectar-pollen mixture or dead arthropods (usually
 spiders). Seven different nest types were identified based on the
 parameters 3, 4 and 5. In both years, several reeds per nest type were
 allowed to grow (minimum 2 reeds in 2018, 15-20 reeds in 2019), which were
 grown at room temperature. Once the individuals were mature, they were
 placed in 70% ethanol and then sent for identification. The taxonomist
 Zsolt Józan identified each two genera of Eumenidae (Ancistrocerus and
 Symmorphus), Megachilidae (Megachile and Osmia) and Pomilidae (Auplopus
 and Dipogon) as well as one genus of Colletidae (Hylaeus) and Crabronidae
 (Trypoxylon). Each nest type was assigned to a genus, except for the two
 genera Ancistrocerus and Symmorphus of the subfamily Eumeninae, which
 could not be distinguished from each other based on the nest
 parameters. <strong>Landscape
 structure</strong> The landscape structure
 surrounding the study sites was quantified by calculating the proportion
 and edge density, which measures the edge length per area of a landscape
 element and thus measures the fragmentation of these elements, of woodland
 patches, the majority of which represents the original natural vegetation
 in this area. Determining the proportion and edge density of a landscape
 element is in most cases sufficient to quantify the structure and
 potential effect of this landscape element on different biological
 variables or processes (Lajos et al. 2020; Lajos et al. 2021a; Lajos et
 al. 2021b). In order to calculate these two landscape metrics, vector maps
 with a radius of 250 m were created in QGIS 2.18.9 (QGIS Development Team
 2009), around the study sites, using the European Terrestrial Reference
 System 1989 Lambert Azimuthal Equal Area (ETRS89/ETRS-LAEA; EPSG: 3035)
 coordinate reference system (Figures 1a and 1b). The centers of these
 circular vector maps were at an approximately equal distance from the
 sampling transects for the wild bees and from the positions of the trap
 nests for the cavity-nesting Hymenopterans (Figure 1c). The vector maps
 were then transformed into raster maps with a raster cell size of 1 × 1 m,
 which were used to calculate the landscape metrics ‘Percentage of
 Landscape’ and ‘Edge Density’ in FRAGSTATS v4.2.1 (McGarigal et al.,
 2002), applying an eight-cell neighborhood rule.
 <strong>Data analyses</strong> All
 statistical analyses were carried out in R v3.6.3 (R Core Team (2020). All
 graphs were created using the R package ‘ggplot2’ (Wickham, 2016). The
 species diversity of bees was assessed by calculating the Shannon's
 Diversity Index (SDI) for each site using the R package ‘vegan’ version
 2.5-6. (Oksanen et al., 2019). Non-parametric Wilcoxon signed-rank tests
 were used to test for significant differences between the abundances and
 the SDI of the eight most abundant wild bee taxa, as well as between the
 abundances of nests built by seven different cavity-nesting Hymenopteran
 per site and study year. Potential habitat affinities
 (= towards the study areas and sites, respectively) were investigated with
 principal component analyses (PCAs) and dendrograms using several
 different functions from the R packages ‘FactoMineR’ and ‘factoextra’
 (Husson et al., 2014). These calculations were based on the numbers of
 specimens sampled for the eight most abundant wild bee taxa and the
 numbers of nests built by the seven different cavity-nesting Hymenopteran
 taxa. The relationships between the proportion and edge
 density of woodland patches around the study sites and the numbers of the
 eight most abundant wild bee taxa or the (occupied) brood cells of the
 seven different Hymenopteran nest types were analyzed using generalized
 linear mixed models (GLMMs) assuming a Poisson distribution from the R
 package ‘lme4’ (Bates et al., 2015), with the study site and year as
 random effects. The two landscape metrics of woodland were scaled prior to
 these GLMMs. The residuals of these GLMMs were tested for uniformity,
 dispersion and outliers using functions from the R package ‘DHARMa’
 (Hartig, 2020). We did not find any significant deviations for the
 residuals of the tested GLMMs in all cases, where significant
 relationships were detected. Finally, we also checked
 for spatial autocorrelation (Moran's I) using the R package ‘ape’
 (Paradis and Schliep, 2019) and reanalyzed the data in all cases, where we
 found significant relationships. Here, we used Generalized Least Squares
 (GLS) models by REML from the R package ‘nlme’ (Pinheiro et al., 2013),
 incorporating a Gaussian correlation structure to correct for spatial
 autocorrelation. The coordinate reference system used for this analysis
 was ETRS89/ETRS-LAEA (EPSG: 3,035), the same one as used for
 mapping.
description: # The role of wild bees and cavity-nesting wasps as ecological indicators
 of the last traditionally managed meadows in Eastern Europe
 [https://doi.org/10.5061/dryad.dr7sqvb76](https://doi.org/10.5061/dryad.dr7sqvb76) ## The dataset consists of the six following .csv-files: 1.    “Species_list_wild_bees”: List of the wild bee species (species and individual numbers) sampled at the study sites during the two study years. The ID-codes of study sites are combinations of capital letters and numbers (e.g. K1, K2, etc.). 2.    “Trap_nests”: List of the nests of different cavity-nesting Hymenopteran taxa (species and individual numbers) found at the study sites during the two study years. The column “Code” consists of the ID-codes of the trap nests, while the column “Reed” lists the ID-numbers of the (occupied) reed stalks (with Hymenopteran nests). The column “Diameter” provides the diameter of the occupied reed stalks in mm. The column “Cells” is the sum of empty and occupied (brood) cells. 3.    “Metrics_bees”: Proportion and edge density of woodland patches (meter/ha) within a 250 m distance around the (study) sites of the wild bee sampling. 4.    “Metrics_nests”: Proportion and edge density of woodland patches (meter/ha) within a 250 m distance around the (study) sites of the trap nests. 5.    “Autocorrelation_bees”: Longitude (“X”) and latitude (“Y”) of the wild bee sampling sites. *Bombus pascuorum* (“BP”) and *Lasioglossum *spp. (“LG”) were the only two wild bee taxa, where the proportion of woodland patches had a significant effect (on their numbers). 6.    “Autocorrelation_nests”: Longitude (“X”) and latitude (“Y”) of the sampling sites with trap nests. “Eumeninae” and “Trypoxylon” were the only two cavity-nesting Hymenopteran taxa, where the edge density or proportion of woodland patches had a significant effect (on their numbers).