Diversity and distribution of spiders ( Arachnida : Araneae ) in dry ecosystems of North Rhine-Westphalia ( Germany )

Abstract: The present study provides a robust data set for ecological planning and conservation of dry ecosystems in western Germany in general and North Rhine-Westphalia in particular. We summarised all available data from recent publications that dealt with spiders in dry ecosystems of North Rhine-Westphalia. Additionally, so far unpublished results of a detailed investigation regarding spiders in sand habitats of the Westphalian Bay that was conducted between 2006 and 2008 are presented. The analysis focussed on the habitat types according to Annex I of the EU Habitats Directive and related habitats. The investigation areas were scattered in the federal state of North Rhine-Westphalia. The data set comprised a total of 84436 individuals from 371 species and 28 families. Overall, an endangerment status is assigned to 68 species. Of these, 12 spiders are in imminent danger of becoming extinct. Two species, Erigonoplus globipes and Meioneta simplicitarsis, are believed to be extinct in North Rhine-Westphalia. Seven species (Dictyna major, Mastigusa arietina, Micaria formicaria, Styloctetor romanus, Thanatus striatus, Theridion uhligi and Xysticus ferrugineus) are new to the arachnofauna of North Rhine-Westphalia.

In Germany, dry ecosystems, such as nutrient-poor sandy grasslands, dry heaths and semi-natural dry grasslands and scrubland facies on calcareous substrates are highly endangered (RIECKEN et al. 2006) and are listed in Annex I of the European Habitats Directive as priority habitat types (BALZER & SSYMANK 2005).Due to increasing cultivation, especially during the past 50 years, and the lack of disturbance (drifting sand, grazing, fire) the area of dry ecosystems has decreased considerably in northern and western Germany (DRACHENFELS 1996, VERBÜCHELN & JÖBGES 2000, JENTSCH et al. 2002, KRATOCHWIL 2004, PARDEY 2004).
Within the framework of conservation and ecological planning, updated and effective data sets concerning species inventories of endangered habitat types as well as distribution and ecology of habitat specialists are imperative.For example, stenotopic species are useful for the evaluation of the nature conservation status of a habitat and biotic communities and may render profuse management guidelines (cf. SCHNITTER et al. 2003).Furthermore, diversity studies and in particular diversity studies of arthropods generally provide a wide spectrum of biogeographical and ecological probes for use in monitoring challenges (GARDNER 1991, KREMEN et al. 1993).In this context, spiders can play an important role since they are abundant, easy to record, occupy a wide array of spatial and temporal niches and respond immediately to habitat changes.Spiders provide robust data sets and statistical rigor within various kinds of ecological surveys (e.g.NEW 1999, SKERL 1999, SCHARFF et al. 2003, SCHMIDT et al. 2005, 2008, FINCH et al. 2007).
Information about the diversity and distribution of spiders in dry ecosystems of western Germany is poor (KREUELS et al. 2008).Thus, the aim of this study is to present a first complete catalogue of spiders that occur in dry ecosystems of North Rhine-Westphalia.For this purpose, we have summarised all available data from the recent literature and added previously unreleased results of detailed investigations concerning the ecology of spiders in sand habitats of the Westphalian Bay.
is sub-Atlantic with a mean annual temperature of 9.5 to 10 °C and mean annual precipitation of 700 to 750 mm.Further study areas were located in the geographic region of the Eifel (Stolzenburg) and the Süder mountains (Hochsauerland: Dahlberg, Kregenberg, Wulsenberg) at an elevation of 450 m a.s.l.& BUCHHOLZ (2006) and KREUELS et al. (2008).

Results
A total of 84436 individuals from 371 species and 28 families were summarised (Table 2).Altogether, for 67 species a status of endangerment is given.Apart from 22 species of category V (endangerment may be assumed), 22 endangered (category 3) and 9 highly endangered (category 2) species, 12 spiders are in imminent danger of becoming extinct (category 1).

Discussion
Seven species have been recorded for the first time for the arachnofauna of North Rhine-Westphalia: According to STAUDT (2009), the rare Dictyna major is mainly distributed in northern Germany, for example in dune habitats (HEYDEMANN 1964, SCHULTZ & PLAISIER 1995) and dry grasslands (BOCHMANN 1941, MERKENS 2002).This species also seems to inhabit dry Pinus forests (SCHAEFER 1980, SIMON 1995).
Mastigusa arientina has so far only been recorded in southern and eastern Germany (STAUDT 2009).The biology and ecology of this rare species is rather unclear.According to MARTIN (1983) Mastigusa arientina is a myrmecophil spider that occurs exclusively in nests of Formica rufa ants.However, SIMON (1995) and KIELHORN & BLICK (2007) found this species at trees and on treetops, respectively.These records may explain the scarcity of this spider since pitfall traps seem to be an inappropriate method to study these strata.
On the other hand, up to now, Thanatus striatus has been found in a variety of different habitat types, such as dry and semi-dry grassland (HÖREGOTT 1958, HEYDEMANN et al. 1994, KUSCHKA 2004  meadows (SPARMBERG & SACHER 1997, BARNDT 2007, FINCH et al. 2007) and dunes (HEYDEMANN 1964, SCHULTZ 1992).T. striatus is distributed all over Germany (STAUDT 2009).MARTIN (1973a) described the theridiid spider Theridion uhligi.He found specimens during an investigation of the nature reserve Rietzer See (cf. MARTIN 1973b).Since then, this species has only been recorded in very few studies in dry grasslands of eastern Germany (PLATEN et al. 1999, JAKOBITZ 2003, STAUDT 2009).Conversely, T. uhligi was recorded in dry grasslands and heathlands in the Netherlands and Belgium ( JOCQUÉ 1977, KEER & VANUYTVEN 1993, PRINSEN 1996, HELSDINGEN 1999) so that the distribution gap is closed now.One further record refers to DUMA (2008) who found T. uhligi in a dry and sandy place of south-eastern Romania.According to HERZOG (1968), BAUCHHENSS (1995), PERNER (1997), PLATEN et al. (1999) and SACHER (2002), the thomisid Xysticus ferrugineus is stenotopic of dry and calcareous grasslands.This species is known from only few locations in central and eastern Germany (STAUDT 2009).
The linyphiid spiders Erigonoplus globipes and Meioneta simplicitarsis are now considered to be extinct in North Rhine-Westphalia: E. globipes was last recorded by KREUELS (1998b).Due to destruction of the former locations caused by land-use, this population has disappeared.Since then, this species has been considered to be extinct in North Rhine-Westphalia (KREUELS & BUCHHOLZ 2006).E. globipes is distributed mainly in higher altitudes of central and southern Germany (BRAUN 1960, BAEHR & BAEHR 1984, BAUCHHENSS & SCHOLL 1985, JOGER 1997) and seems to be absent in the lowlands (STAUDT 2009).According to all the previous records, this species is stenotopic for dry calcareous grasslands (BAEHR 1988, KÖHLER et al. 1989, PERNER 1997).Meioneta simplicitarsis is a rare species that has until now been found in eastern Germany (e.g.SACHER & BREINL 1999), Rhineland-Palatinate (WEBER 1999) and North Rhine-Westphalia (CASEMIR 1982).It seems to prefer dry grasslands (BRAUN 1969, BUCHAR & RŮŽIČKA 2002) but also occurs in wet meadows and pastures (HEIMER & NENTWIG 1991, KREUELS & BUCHHOLZ 2006).
When working with the present data one has to consider several taxonomical problems.For example, Alopecosa accentuata and Alopecosa barbipes are closely related species that were once considered to be synonyms.However, several studies have confirmed the separation of both species (DAHLEM et al. 1987, CORDES & HELVERSEN 1990, CORDES 1995, VINK & MITCHELL 2002).On the other hand, at least the identification of female specimens is very difficult, while males can be clearly distinguished by the hair coat on Tibia I. Furthermore, both species show a different phenology and distribution (CORDES & HELVERSEN 1990, STAUDT 2009).Nevertheless, SCHMITT (2008) stated that several authors might have ignored the differences between both species found during previous studies, which makes the current status of A. accentuata and A. barbipes questionable.Consequently, we checked specimens from most of the lowland sites (2,5,7,9,10,19,21,30) and one highland site (16).As a result of this, we state that all lowland records belong to Alopecosa barbipes while individuals from the low mountain ranges belong to A. accentuata.Thus, former data on A. accentuata that were published by BUCHHOLZ & HARTMANN (2008) and BUCHHOLZ (2008) have to be transferred to A. barbipes.
Further taxonomic questions arise concerning Dicymbium nigrum brevisetosum which was first described by LOCKET (1962) and WIEHLE (1965) as a form and recognised as a species by LOCKET et al. (1974).Later, THALER (1986) discussed the existence of further forms of Dicymbium nigrum s. str. in the southern Alps.Finally, ROBERTS (1987) downgraded D. n. brevisetosum back to a form.This taxonomical problem is not completely solved yet, but differences in the hair coat of Tibia I which is considerably shorter in D. n. brevisetosum might justify the separation of both as valid species.Both have been recorded from Germany (WIEHLE 1965, HARMS 1987) but it is assumed that numerous records of Dicymbium nigrum s. str.might belong in fact to D. n. brevisetosum since, for example, drawings of the first one given in the reference guide of NENTWIG et al. (2003) in truth refer to D. n. brevisetosum (cf. WIEHLE 1960(cf. WIEHLE , 1965)).Hence, we checked all available material and exclusively found specimens with short hair coats on Tibia I which according to ROBERTS (1987) indicated the occurrence of only Dicymium nigrum brevisetosum within the study area.Consequently, records for Dicymbium nigrum published by BUCHHOLZ & HARTMANN (2008) and BUCHHOLZ (2008) have to be adjusted to D. n. brevisetosum.
Finally, we have to keep in mind the fact that several parts of North Rhine-Westphalia are hitherto poorly investigated.Especially for the eastern und southern parts of the federal state (e.g.Sauerland, Weserbergland), as well as for the mountains of the Eifel, faunistic records are almost entirely missing (KREUELS et al. 2008).This is a drawback for this study since large parts of the semi-natural dry grasslands and scrubland facies on calcereous substrates are situated in these regions and thus remained undersampled yet.As opposed to this, the coverage level for dry and sandy heathlands and grasslands has been thoroughly improved within detailed studies during the last years.

familiy [no species] / species
End Dis study area [no of sites] sum