LOCALITIES

Mites were collected in 1992 and 1993 in the vicinity of Obergurgl (11°02′E, 46°52′N), the silicate bedrock area of the Ötztal Alps (Fig. 1), at various altitudes above timberline ranging from ∼2000 m a.s.l. in the low alpine zone up to ∼3000 m a.s.l. in the low nival zone (Reisigl and Pitschmann, 1958; Reisigl and Keller, 1987; Meyer and Thaler, 1995). The environmental conditions prevailing in this region have been described in detail by Reisigl and Pitschmann (1958), and more recently by Janetschek et al. (1987). Low temperatures, a short growing season, reduction of habitat structure, little plant cover, and the effect of wind and snow cover distribution are the most important ecological factors influencing montane biota in this area (Meyer and Thaler, 1995). Because, for the most part, only adult specimens of the rhagidiid mites can be reliably identified to species and because these occur in cool montane habitats at the end of the growing season, hand collections were timed from the end of August to the beginning of September when the alpine landscape was not yet covered with snow.

Samples of mites (S1–S10) were collected in 10 various localities in six different alpine habitats and altitudinal zones (ALP1–ALP6) (Table 2).

COLLECTION

The distribution of rhagidiid mites in nature is not random. Their preferences for particular microhabitats where they are aggregated are clearly visible to a collector. A really random and unbiased sampling of these mites is therefore difficult. Epigeic and hypolithic mites, i.e., mites living in voids under stones, were collected by way of hand sorting using a small aspirator containing ethanol as a preservative. To standardize a sampling effort, the greatest possible number of individuals was always collected in the investigated localities (Magurran, 2003). Only limited kinds of sampling techniques are available and appropriate for rhagidiid mites inhabiting deep underground voids in scree slopes. Large pitfall traps made of rigid plastic, about 13 cm high and 10.5 cm in diameter (Růžička, 1988) were positioned ∼50–100 cm under the surface of the scree slopes. The traps contained an aqueous mixture of 7% formalin and 20% glycerol, plus a few drops of detergent. They were left in place for 1 year, from 4 June 1991 to 26 June 1992, after which they were removed and the catch was processed in the laboratory. Mites, initially preserved in ethanol, were transferred to lactic acid in temporary slide preparations (Krantz, 1978), examined under a standard light microscope under a bright field and identified to species (Zacharda 1980, 1995a, 1995b, 1996, 2000a, 2000b, 2000c, 2000d).

SPECIES DIVERSITY MEASURES

Species abundance data were plotted as a rank/relative abundance graph (the Whittaker plot) to estimate and illustrate an expected impact of different alpine zones (ALP1–ALP6) on the assemblages of rhagidiid mites with respect to their species heterogeneity (species richness and evenness) in the alpine environment, (Magurran, 2003). Numerical species richness was estimated by a Chao1 nonparametric estimator (Magurran, 2003, p. 87), diversity by Simpson's index (D), and species evenness by Simpson's E1/D index (Magurran, 2003, p. 114–116). The Simpson's index was computed by the BioDiversity Professional v.2 software package ( http://www.nhm.ac.uk/zoology/bdpro).

ENVIRONMENTAL DATA SOURCES

Ecological interrelations of mites to their environment were observed and data collected for further numerical multivariate analysis. The following data were recorded for each locality: (1) quantitative: (i) altitude (range 2000–3050 m a.s.l.), (ii) insolation was represented by insolation index (cos [aspect − 202.5°] × tg [slope]; Geiger, 1966); (2) semiquantitative: (iii) moisture (ordinal scale 0–4: 0—dry, 1—slightly moist, 2—moist, 3—moist to wet, 4—wet), (iv) vegetation cover (ordinal scale 0–3: 0—bare ground, 1—sporadic small patches covering less than 40% of ground surface, 2—patches covering 40–60% of ground surface, 3—patches covering 70–100% of ground surface); (3) categorial (indicator, so-called “dummy” variables): alpine zones (ALP1–ALP6) (see above in the description of localities).

NUMERICAL ANALYSIS

The species abundance data were log-transformed for all analyses. Samples of species assemblages were clustered considering their co-occurrences in the same sample by Bray-Curtis single linkage similarity using group-average clustering. The cluster analysis was computed by the BioDiversity Professional v.2 software package ( http://www.nhm.ac.uk/zoology/bdpro).

To describe supposed interrelations between individual species and their assemblages to different environmental factors such as altitude, vegetation, stand cover, and insolation in their montane habitats, the multivariate analysis was used (Jongman et al., 1987, Legendre and Legendre, 1998). Both unconstrained and constrained ordinations were additionally computed in Canoco for Windows v. 4.5 (ter Braak and Šmilauer, 2002). The interspecific correlations were computed by Principal Component Analysis (PCA). Subsequently, the positions of alpine zones were passively projected as indicator “dummy” variables (Lepš and Šmilauer, 2003, pp. 8, 155–156). The relationships between the species and the environmental variables were studied by direct gradient analysis (constrained ordination; see Lepš and Šmilauer, 2003), and the statistical significance of the species-environment relation was tested with a Monte Carlo permutation test (MCPT) in Canonical Correspondence Analysis (CCA). Although the most striking environmental gradient was the altitudinal one (we expected the linear response of species to environment), we selected a method with unimodal species response to environment due to the analysis results of ecological gradient length in Detrended Correspondence Analysis (the beta diversity in community composition, measured as the length of the largest gradient, was 4.458; for an explanation see Lepš & Šmilauer, 2003, p. 51). For further analyses in CCA, the centering by species and biplot scaling were selected, and the standardization by species was selected due to the species differences in quantity. The explanatory effects of particular environmental variables were evaluated in MCPT by the stepwise procedure that selects variables with the best fit of species data. The MCPT procedure tests the significance of regression (F-statistics and probability of Type I error) under the null hypothesis of independence of species data on the environmental variables. Number of permutations was arbitrarily assigned to 999. The significantly important environmental variables were visualized by the ordination biplots in Cano Draw v. 4.12 (ter Braak and Šmilauer, 2002). Eigenvalues (λ) mean explanatory power of axes, and they express their relative importance (Lepš and Šmilauer, 2003).

FAUNISTICS

A total of 238 specimens of collected rhagidiid mites belonging to 6 genera were examined, and 21 species were identified. Among them, endemic (E), Palearctic (P), and Holarctic (H) species can be recognized (Table 1).

DIVERSITY

Poecilophysis pseudoreflexa, Rhagidia parvilobata, Foveacheles unguiculata, and F. halltalensis were the most abundant species, and they occurred in 6, 5, 4, and 4 localities, respectively. Troglocheles archetypica occurred in 3 localities in the high alpine and subnival zones. Other species occurred sporadically, with only a few individuals, hence their abundance was low. Rhagidia diversicolor occurred plentifully in only one locality (Lc. 8) in the high alpine zone (Table 3).

The lowermost abundance of rhagidiid mites was indicated in the alpine meadow with the Curvuletum plant cover (ALP3) where only one specimen of rhagidiid mite was collected (Fig. 2). Troglocheles aggerata has its narrow niche strictly confined to cool, moist underground scree voids. Poecilophysis pseudoreflexa, Rhagidia parvilobata, Foveacheles unguiculata, F. halltalensis, and partly also Troglocheles archetypica are species with broad, overlapping niches. The assemblages of rhagidiid mites collected in different alpine zones ALP1, ALP2, ALP4, ALP5, and ALP6 (see Table 2), consisted of 2 to 9 species. The respective values of Simpson's index (D) for diversity, evenness measure E1/D, and Chao 1 species richness estimate are presented in Table 4.

CLUSTER ANALYSIS

Considering the co-occurrences of different species in the same sample (Table 3), the cluster analysis of samples 1 to 10 collected in 10 different localities (Table 2) confirms that there is a group of samples (4–10) collected from the mid-alpine zone (ALP4) to the high alpine (ALP5) and the low nival (ALP6) zones that is clearly separated from the other samples (Fig. 3). The underground scree voids, sample 1, are a unique habitat with endemic Troglocheles aggerata as the dominant species. Similarly, the lower part of the low alpine zone (ALP2), with Rhagidia distisolenidiata, R. gigas, Poecilophysis pratensis, and P. saxonica that occurred only there (cf. Table 3), differs strikingly from the other samples. Also, the dense Curvuletum–plant cover, sample no. 3, where only 1 specimen of rhagidiid mite was collected, differs from the other samples strikingly. Because many species were common in samples 7 to 10, the high alpine zone and the low nival zone with the respective altitudes varying only from 2700 to 3050 m a.s.l. could be amalgamated with a common assemblage of species of rhagidiid mites. But some of these species, such as Poecilophysis pseudoreflexa, Foveacheles halltalensis, or Troglocheles archetypica, become rare with altitude, similarly as Rhagidia parvilobata, which occurs from the low alpine zone (ALP2) to the mid-alpine zone (ALP4).

ENVIRONMENTAL ANALYSIS

A few groups of species having some affinities to different alpine zones can be distinguished (Fig. 4). Troglocheles aggerata and Evadorhagidia oblikensis are strictly confined in moist to wet interstitial voids of the bare scree slope (ALP1). On the opposite side of the altitudinal gradient, in the low nival zone (ALP6), a group of species consisting of Foveacheles cegetensis, Evadorhagidia bezdezensis, and Coccorhagidia pittardi is well distinguished. The high alpine zone (ALP5) has the highest species richness and, probably, endemism as the majority of newly described taxa of rhagidiid mites, i.e., Troglocheles archetypica, Foveacheles proxima, and Rhagidia longipes were collected only there. Poecilophysis pratensis, Rhagidia distisolenidiata, and partly also Rhagidia gigas are psychrophilic, forest as well as meadow-inhabiting species, and here occur in the low alpine zone (ALP2). The mid-alpine zone (ALP4) is inhabited by Poecilophysis pseudoreflexa, Poecilophysis spelaea, Evadorhagidia corcontica, and Foveacheles unguiculata.

EFFECTS OF ENVIRONMENTAL FACTORS

Of all of the evaluated environmental variables, (i.e., alpine zones, altitude, moisture, vegetation cover, heat index), only three were significant (Table 5). As shown in Figure 5, species having some affinities to specific environmental factors can be distinguished. They are separated into four quadrats of the diagram. ALP1 presents the uniqueness of the deep scree underground, and the species assemblage is fully covered by the species-environment correlation (Table 6, the 1st canonical axis λ = 1). The altitudinal gradient (ALTIT) (Fig. 5) proved to be important as the significant complex factor and represents variability relevant to axes 2 and 3. Moisture (MOIST) proved to have a different effect because it is an important environmental factor influencing abundance of mites (number of specimens = 10.714 MOIST − 8.243; R² = 0.368) but has no direct relation to species identity. Both moisture and altitude correlate negatively with the second ordination axis (Table 7). The position of Poecilophysis pratensis, P. saxonica, and Rhagidia distisolenidiata in the biplot diagram is opposite the moisture factor (Fig. 5).

PALEARCTIC SPECIES

Evadorhagidia oblikensis, E. corcontica, E. bezdezensis, Foveacheles cegetensis, and Poecilophysis spelaea have a Palearctic pattern of distribution. P. spelaea is a troglodytic species that occurs frequently in European caves from Scandinavia (Hippa et al., 1989) to the Balkans (Thor and Willmann, 1941). It also occurs in cool and moist interstitial habitats of stony debris in central Europe (Růžička and Zacharda, 1994). F. halltalensis, which occurs in the Ötztal Alps from mid- to high alpine and subnival habitats, was also collected in subterranean cool scree voids at ∼300 m altitude in northern Bohemia (Zacharda, unpublished data).

HOLARCTIC SPECIES

Rhagidia gigas, R. parvilobata, R. distisolenidiata, R. diversicolor, Poecilophysis pseudoreflexa, P. pratensis, P. saxonica, P. wankeli, and Foveacheles brevichelae are species with a Holarctic pattern of distribution. P. pseudoreflexa is the dominant, most abundant species in the mid- to high alpine and subnival zones of the Ötztal Alps.

Coccorhagidia pittardi is an arctic-alpine species that was discovered in Alaska (Strandtmann, 1971), but later was also collected in the High Tatras, Slovakia, at an altitude of 2200–2367 m a.s.l. (Zacharda, 1980) and in the Himalaya at 3900 m a.s.l. (Zacharda and Daniel, 1987). Recently, the species was also discovered in the Ardovska cave, in the Slovak Paradise National Park, Slovakia, where it can be considered a periglacial relict (Zacharda, unpublished data). C. berlesei Sig Thor (Thor and Willmann, 1941) and C. divergens Mihelčič, 1957, were also reported from high altitudes in the Alps (Franz, 1954; Mihelčič, 1957). However, these taxa were described only very briefly, and are still of uncertain taxonomic placement. One of them may be conspecific with Coccorhagidia pittardi.

ENDEMIC SPECIES

Representatives of the genus Troglocheles can be considered endemic in the Alps and adjacent mountain systems such as the Pyrenees (T. vandeli Zacharda, 1987), the Swabian Alb in Germany (T. gineti sensu Rack, 1974), the Karst Alps in Slovenia [T. strasseri (Willmann, 1932)], and the Venetian Alps in Italy [T. conciana (Lombardini, 1951)]. They occur mostly in caves, and T. strasseri, T. strasseri tiroliensis, T. gineti, T. vornatscheri, and also in part T. vandeli are troglomorphic, i.e., morphologically adapted to caves (Zacharda, 1979). In the Pleistocene-glaciated regions of the Alps, these species invaded cave systems during the post-Pleistocene, but not in regions that were not glaciated. There, the mites could occupy the cave habitats well before the period of Pleistocene glaciation.

T. aggerata lives in open voids under the surface of alpine bare scree slopes and it is morphologically adapted to this environment (Zacharda, 2000b). Our results of cluster analysis corroborate ecological divergence of this scree underground habitat (ALP1) and confirm its significance and importance for conservation and adaptive evolution of chelicerates (Růžička, 1999).

Only T. archetypica is epigeic in the high alpine to subnival zones. T. archetypica either evolved from a paleoendemic ancestor in alpine unglaciated nunataks or marginal unglaciated zones of the Alps and subsequently dispersed to unglaciated alpine biotopes during the postglacial Holocene, or it evolved quite recently during the Holocene (Zacharda, 2000b).

Rhagidia longiseta, Foveacheles unguiculata, and F. proxima are currently known only from the Alps and can also be considered to be endemic.

A specific assemblage of rhagidiid mites with a low diversity was found in the deep underground voids of a bare scree slope just at an upper limit of timberline (ALP1) where only two species were collected despite the pitfall traps being placed there for one year. Our results document that this habitat is occupied by different species than occur in the high altitude screes of alpine non-forested zones. In contrast, the mid-alpine zone (ALP4) and the high alpine zone (ALP5) were the most rich in species. The numerical nonparametric estimator of species richness Chao1 provided the same values of species richness in the scree underground voids (ALP1) to the mid-alpine zone (ALP4) and slightly to moderately increased values in the high alpine zone (ALP5: 9.5) and the low nival zone (ALP6: 11.5). This means that in the high alpine zone and the low nival zone further species of rhagidiid mites rarely occurring in the local assemblages might be expected to be found and that the faunal list of species from the Ötztal Alps (Table 3) should not be considered definitive. This assumption is supported by findings of subadult specimens of the genera Evadorhagidia and Foveacheles that are of uncertain taxonomic status.

As indicated by similarly steep slopes of chart curves for low, mid-, high alpine, and low nival zones (ALP2, ALP4, ALP5, ALP6) (Fig. 2) and values of evenness measure E1/D (Table 4), the more the assemblages of mites are rich in species, the more even they are as well.

The numerical environmental analysis has also corroborated that there are the positive (+) as well as the negative (−) interrelations between occurrence and abundance of assemblages of the rhagidiid mites in the different montane habitats and quantitative, semiquantitative, and categorial environmental gradients such as the altitude, substratum humidity (moisture), and alpine altitudinal zones (Table 7). It is obvious that even though the altitudinal and moisture gradients are of different ecological significance, they both have influence on the species pattern positioned in the opposite direction to the environmental factor arrows in the ordination diagram (Fig. 5, the 2nd axis). Although dryness may be considered to be an opposite to moisture, it proved to be bound with the occurrence of Poecilophysis pratensis, P. saxonica, and Rhagidia distisolenidiata. However, these species are not strictly confined to dry habitats because they occur in various niches of terrestrial microhabitats in middle altitudes of highlands (Zacharda, 1980).

No other relevant information on the ecological interrelations between rhagidiid mites, their habitat affinities, and the respective environmental factors can be discussed because they are not known.