Oribatid mite assemblages
In total, 17,611 adult oribatid mite individuals were collected in the Swabian Alb and 14,931 in the Schorfheide, belonging to 100 taxa in total (Table 1). In the Swabian Alb, 72 taxa were found in forests (15 parthenogenetic, 57 sexual) and 62 in grasslands (15 parthenogenetic, 47 sexual). Species richness was slightly lower in the Schorfheide; in forests, 70 taxa (25 parthenogenetic, 45 sexual) and in grasslands 34 taxa (8 parthenogenetic, 26 sexual) were represented. Similarly, oribatid mite diversity was consistently higher in forests than in grasslands albeit lower in the Schorfheide than in the Swabian Alb (Fig. 1; habitat: F1,287 = 124.839; region: F1,287 = 37.112, both p < 0.001).
NMDS analysis, including sexually and parthenogenetically reproducing oribatid mite species, clearly separated habitats and regions (Fig. 2a). However, assemblages were more similar to each other in the same habitat of different regions than among habitats in one region. NMDS analysis of sexual species revealed a similar pattern with a broader overlap of forest assemblages (Fig. 2b). In contrast, oribatid mite assemblages of parthenogenetic species were highly similar (Fig. 2c). The pattern of similar assemblages in similar habitats among regions is also present in the size CWM (Fig. 3; habitat: F1,56 = 113.838, p < 0.001; region: F1,56 = 3.268, p = 0.076). Assemblages in forests comprise smaller species than in grasslands which was more pronounced in the Schorfheide than in the Swabian Alb (habitat*region: F1,56 = 6.558, p = 0.013).
In both regions, the majority of adult oribatid mite individuals occurred in forests; this pattern was more pronounced in the Schorfheide (74.8 and 89%, respectively; Fig. 4 middle; habitat: F1,287 = 64.672, p < 0.001; region: F1,287 = 4.7, p = 0.031; habitat*region: F1,287 = 4.805, p = 0.029).
Mode of reproduction, sex ratio and number of eggs
The percentages of sexual and parthenogenetic individuals and species were similar in grassland and forest habitats in the Swabian Alb and in grasslands in the Schorfheide: with about 75%, sexuality dominated over parthenogenesis (Fig. 4 left and right). By contrast, Schorfheide forests had a higher percentage of parthenogenetic individuals (58.6%) and a relatively high percentage of parthenogenetic species (37.3%) (Table 2).
The percentage of females in sexual and parthenogenetic oribatid mite communities significantly differed with the reproductive mode and region (Fig. 5, Table 3). In sexual species 55.3 and 54.9% females were present in the Swabian Alb and the Schorfheide, respectively. The parthenogenetic part of the oribatid mite community had almost 100% females in grasslands and had only a few males in forests (99.95% females).
The sex ratio of parthenogenetic and sexual species in forest and grassland communities was consistent among regions (Table 1). In sexual species, sex ratios varied between ca. 30% (Ophidiotrichus tectorum, Oribatella calcarata, Hermannia gibba, Damaeus spp.) and 70% females (Ceratozetes gracilis, Achipteria quadridentata; Table 1) and averaged at about 59%. Parthenogenetic species normally comprised 100% females, but rare, spanandric males were found in the genus Tectocepheus and in Oppiella nova (Table 1).
The average percentage of gravid female was generally higher in sexual than in parthenogenetic species (71 vs. 63%) and higher in the Swabian Alb than in the Schorfheide (72 vs. 62%; Fig. 6, Table 4). In both habitats and both regions, sexual species had significantly more eggs per gravid female than parthenogenetic species (2.97 vs. 1.81 on average; Fig. 7, Table 5).
Influence of land-use intensity
The community weighted mean (CWM) of body sizes was not affected by any land-use parameter neither in forests nor in grasslands (Table 6, for statistical values see Online Appendix 2). Diversity of oribatid mite assemblages correlated negatively with all forest-management parameters except wood harvesting in the Swabian Alb, and with the proportion of dead wood with saw cuts and the combined forest-management index in the Schorfheide (Table 6, Online Appendix 3). In grasslands, land-use intensity had a stronger impact on oribatid mite diversity than on density. In both regions, diversity was significantly lower on plots with a high land-use index and in the Swabian Alb additionally on plots with high grazing intensity. In contrast, diversity was correlated positively with high mowing and fertilization intensity in the Schorfheide (Table 6, Online Appendix 3).
In the Schorfheide, oribatid mite density significantly dropped with increasing proportion of dead wood with saw cuts in forests and with higher grazing and fertilization intensity in grasslands (Table 6, Online Appendix 3). However, density in the Swabian Alb was unaffected by either grassland or forest land-use parameters.
A high forest management index and a high number of non-native trees significantly correlated with lower proportion of sexual individuals in forests in the Swabian Alb, but mowing in grasslands was positively correlated with the proportion of sexual individuals in the Schorfheide (Table 6, Online Appendix 4). Accordingly, the proportion of females in sexual species was only affected in grasslands in the Schorfheide; the proportion of females was lower at high land-use indexes and high grazing intensity whereas intensive mowing was correlated positively with the proportion of females in sexual species.
In sexual species, the proportion of gravid females dropped with an increasing number of non-native trees, tree harvesting and dead wood with saw cuts; in grasslands, a higher proportion of gravid females was present on plots with high fertilization (Table 6, Online Appendix 5). In parthenogenetic species, gravidity positively correlated with high fertilization in the Swabian Alb and with high mowing intensity in the Schorfheide. However, the number of eggs per gravid female in sexual species was not influenced by any land-use parameter. In parthenogens, numbers of eggs per gravid female increased in the Swabian Alb but decreased in the Schorfheide with increasing tree harvesting.
On the species level, land-use effects in forests were more pronounced than those in grasslands (Table 7, Online Appendix 6). In sexual species, about 6% were significant ‘losers’ to a high forest management index and about 4 and 7%, respectively, were ‘losers’ to tree harvesting and the proportion of non-native trees. A high proportion of dead wood with saw cuts had by far the greatest impact, resulting in 75% ‘losers’ among sexual species. Similarly, a high percentage of dead wood with saw cuts was correlated negatively with 87.5% of parthenogenetic species. ‘Winner’ species were more abundant in sexuals than in parthenogens, especially for the forest management index (about 12%) and the percentage of non-native trees (about 10%).
In grasslands, we found only about 2% ‘losers’ in sexual species concerning the combined land-use index. On the other hand, about 7, 4 and 2% ‘winners’ were present in sexuals for the land-use index, mowing and fertilization, respectively. Parthenogenetic species did not react as ‘losers’ to any land-use parameter, but about 7% ‘winners’ were found on plots with high grazing intensity. On average, sexual and parthenogenetic oribatid mite species suffered equally from high land-use intensity in forests (23.3 vs. 22.9%) and grasslands (0.5 vs. 0%). On the other hand, ‘winner’ species, i.e., those species found on plots with high land-use intensity, were more common among sexual species in both forest (5.9 vs. 3.1%) and grassland (3.3 vs. 1.7%) habitats.