Spider Biodiversity Potential of an Ungrazed and a Grazed Inland Salt

Biodiversity and Conservation 6, 75±88 (1997) Spider biodiversity potential of an ungrazed and a grazed inland salt meadow in the National Park `Neusiedler See-Seewinkel' (Austria): implications for management (Arachnida: Araneae) KLAUS PETER ZULKA*, NORBERT MILASOWSZKY and CHRISTA LETHMAYER Institute of Zoology, University of Vienna, Althanstr. 14, A-1090 Vienna, Austria Received 7 June 1995; revised and accepted 20 November 1995 To assess the biodiversity potential of an ungrazed and a grazed inland salt meadow in the Seewinkel (Eastern Austria), spider assemblages were recorded by pitfall trapping for 1 year. Both species assemblages consisted, to a large extent, of rare species of conservation interest. The species assemblage of the grazed site was dominated by Pardosa agrestis, but highly speci®c halotopobiontic species also occurred in higher numbers. Halotolerant species were also present in the ungrazed meadow, but their individual number was much lower. The species composition of this site re¯ects the more balanced microclimatical situation of the high sward. Comparison of the two assemblages with 207 other meadow spider assemblages of Central Europe shows a separated position, especially of the grazed site assemblage. High similarities with assemblages of meadows with a similar vegetation structure indicate a high importance of management. Considering the high proportion of rare species on both sites, the best management of the salt meadow and pan shores of the Seewinkel should combine areas of light grazing with ungrazed areas. However, the proportion of these parts and the intensity of grazing still remains to be determined by quantitative experiments. Keywords: grazing; pasture; halophily; conservation; similarity index. Introduction The loss of biological diversity due to human impact is a ubiquitous phenomenon in the 20th century (e.g. Ehrlich and Ehrlich, 1981). However, not all biotopes are equally af- fected by this decline, and not all kinds of biotopes are equally important for the main- tenance of biodiversity. Inland salt sites are probably among the most sensitive and the most signi®cant sites in this respect. They usually house a specialized fauna and ¯ora of tolerant species (or locally adapted populations). Salt sites are often very small, isolated and patchily distributed, which implies all problems of extinction probability analysed by island ecology (Sim- berlo, 1988; Saunders et al., 1991). They are often surrounded by highly managed or polluted agricultural land. A small change in management practice or hydrology, e.g. lowering of the groundwater table, can lead to a complete disappearance of the typical *To whom correspondence should be addressed. 0960-3115 Ó 1997 Chapman & Hall 76 Zulka et al. fauna and ¯ora; even if they are left physically intact (e.g. MuÈller-Motzfeld et al., 1993). Consequently many species lists in Red Data Books consist, to a large extent, of halotopobiontic species (e.g. MuÈller-Motzfeld, 1987; JaÈch, 1994). The `Seewinkel', the area between Neusiedler See and the Hungarian border (Eastern Austria), is probably the most important region of inland salt sites in Central Europe. About 6% part of the soils of the Seewinkel contain high amounts of soda (Nelhiebel, 1980). However, since the turn of century the number of alkaline pans has declined dramatically from 116 (LoÈer, 1982) to about 40 today. Even the remaining ones are often in a poor condition. When, in 1994, the National Park `Neusiedler See-Seewinkel' was established, large parts of the alkaline pan areas became included. Clearly, not all conservation problems can be solved simply by declaring a national park (Herzig, 1991). One threat for the typical landscape is the spread of reed vegetation, overgrowing the alkaline pans and the Puccinellia peisonis meadows around them. Fes- tetics (1970) described the negative eects of too low grazing rates, leading to a trans- formation of the original and typical salt pan shores into the swampland of much lower conservation value, especially for birds. Thus, in 1988 a grazing programme was established at the `Illmitzer Zicksee' to reduce the negative in¯uence of the growing reed cover (Rauer and Kohler, 1990) and to enlarge the breeding area for birds. However, grazing might have a negative in¯uence on epigean arthropods. Many animal groups reach much higher population densities in ungrazed meadows (Morris, 1968). The spider fauna of an intensively grazed pasture was shown to be impoverished compared to the margin and consisted mainly of widespread pioneer species (Maelfait and de Keer, 1990). All spider species requiring more complex vegetation structures (e.g. web-formers) are signi®cantly reduced by grazing (Gibson et al., 1992). Thus, the main aim of this study was the assessment of the faunal potential of a short- grass versus an ungrazed salt meadow. Previous work on the terrestrial invertebrate fauna of the Seewinkel area is very limited, but earlier studies have already indicated that these salt habitats house highly speci®c arthropod communities (Machura, 1935; Franz et al., 1937; KuÈhnelt, 1955; Kritscher, 1958; Nemenz, 1958). Materials and methods Study area The study area comprises two meadows situated about 10 km North-West of Illmitz (47ë46¢N, 16ë46¢E) near the `Illmitzer Zicksee' salt pan. The unmanaged meadow covers an area of about 110 ´ 50 m and lies at 117 m above sea level. It is sharply bordered by vineyards on two sides and indistinctly by invading reed vegetation on the other two sides. Both pitfall trapping and vegetation analysis (Table 1) were performed in the centre of the meadow. The managed meadow lies about 1100 m apart (height 116 m, area 0.2 ha). It is surrounded by introgressing reed vegetation on one side, vineyards on two sides and a road. Grazing started in 1989 with ¯uctuating intensity (0.1±0.5 cows ha)1). In 1990, the year of study, the meadow was extensively grazed from May to October by about 0.8 cows ha)1 (Aberdeen-Angus) (cf. Rauer and Kohler, 1990; Lethmayer, 1992). Soil conditions and vegetation composition of the two sites are fairly similar: both lie on solonchak soda soils and both meadows are dominated by Puccinellia peisonis (Table 1), being a part of the endemic Atropidetum peisonis (Franz et al., 1937) plant association Spider biodiversity and management 77 Table 1. Vegetation at the two sites Ungrazed Grazed Area of vegetation sample (m2)2520 Vegetation cover (%) 100 75 Maximal vegetation height (cm) 70 20 Average vegetation height (cm) 50 20 Species Covera Puccinellia peisonis 54 Suaeda maritima 1 Odontites rubra 1 Achillea millefolium + Aster tripolium ssp. pannonicus 2+ Atemisia santonicum ssp. patens + Lepidium cartilagineum ++ aAccording to Braun-Blanquet (1964). (Mucina et al., 1993). However, the structure of the vegetation is completely dierent. The vegetation cover in the grazed meadow is incomplete due to trampling, which allows additional plant species to enter the habitat (e.g. a small patch of Lepidium cartilagineum, Table 1). The sward is uniformly short, leading to high insolation, evaporation and salt incrustations on the soil surface. Thus, microclimatical conditions are much more extreme than within the homogeneous sward of the ungrazed meadow (cf. Lethmayer, 1992) Sampling methods Spiders were sampled using ®ve pitfall traps at each site (plastic cups with a diameter of 7 cm and a height of 10 cm, covered with a tin roof, half-®lled with 5% formalin and containing a small amount of detergent). The traps were arranged in a quadrate with one trap in the centre (cf. Lethmayer, 1992). Pitfall trapping was conducted from 9 April to 26 October 1990. The traps were emptied at exact 10-day intervals. The contents of all ®ve traps were pooled and stored in 70% ethanol. Analysis The two spider assemblages obtained were compared to a set of 207 other Central Eur- opean assemblages from the literature. Most assemblages came from grassland, but some came from agricultural land and wetland formations. All assemblages had been sampled by pitfall trapping during at least one complete vegetation period. Two similarity indices were used: Sùrensen's quotient, comparing only presences and absences, and Renkonen's coecient of similarity, taking also dominance (percentage of total individuals) into ac- count (MuÈhlenberg, 1989, p. 287). However, for the comparison by Renkonen's index 13 assemblages had to be excluded from the analysis because no exact individual numbers were given in the publications. 78 Zulka et al. Results Species composition A total of 4742 adult individuals was caught, about two thirds of them in the grazed meadow (Table 2). The species number was slightly higher on the grazed plot, the a-diversity value (as measured with the Brillouin index, Magurran, 1988) slightly lower. Of 85 species, 31 occurred on both sites, resulting in a Sùrensen quotient of similarity of 0.53 (Table 4). Only four species (Ozyptila simplex, Pardosa prativaga, Alopecosa pulverulenta and Trochosa ruricola) occurred on both sites with dominances >1% (Table 2). Thus, even Table 2. Dominant species of both sites and assemblage parameters of the full data set Species Site Number of Dip Signi®cance a Ungrazed Grazed peaks of intensity male activity Pardosa prativaga (L. Koch) 37.51% 2.23% 1 Pirata latitans (Blackwall) 9.71% ± 1 Pocadicnemis juncea Locket & 8.24% 0.09% 1 Millidge Syedra apetlonensis Wunderlich 6.71% 0.13% 2 1.68 p >0.5 Drassyllus lutetianus (L. Koch) 5.11% 0.38% 1 Trochosa ruricola (De Geer) 4.73% 1.70% 1 Trichopterna thorelli (Westring) 2.49% ± 1 Pardosa maisa Hippa & Mannila 1.67% ± 1 Clubiona subtilis L. Koch 1.53% 0.28% ? Zelotes latreillei (Simon) 1.47% 0.09% ? Micrargus subaequalis (Westring) 1.15% ± 1 Pardosa agrestis (Westring) 0.26% 46.64% 2 3.00 p > 0.01 Ozyptila simplex (O. P.-Cambridge) 8.56% 17.66% 1 Silometopus reussi (Thorell) ± 8.15% 2 4.59 p > 0.01 Zelotes mundus (Kulczynski) ± 5.35% 1 Alopecosa pulverulenta (Clerck) 1.02% 2.08% 1 Pardosa cribrata Simon ± 1.64% 1 Xerolycosa miniata (C.

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