Diptera, Syrphidae) in the Elbe Floodplain

Internat. Rev. Hydrobiol. 91 2006 4 341–363 DOI: 10.1002/iroh.200510889 FRANK DZIOCK Technische Universität Berlin, Biodiversity Dynamics of Terrestrial Ecosystems, Rothenburgstr. 12, D-12165 Berlin; e-mail: [email protected] Life-History Data in Bioindication Procedures, Using the Example of Hoverflies (Diptera, Syrphidae) in the Elbe Floodplain key words: life history traits, multivariate statistics Abstract This is the first study to relate syrphid life history traits to environmental variables with a multi-trait approach. We aimed to answer two questions: 1. Do syrphid species respond to small scale changes in environmental variables in seasonally flooded grasslands in a Central European floodplain (Elbe)? 2. Can species response to environmental variables be explained by the biological characteristics of the species expressed by their life history traits? Despite their large mobility, syrphids did respond signifi- cantly to small scale changes in environmental variables (groundwater (GW) depth, cation exchange capacity, amplitude of variation of the GW-depth). On the other hand, the biological traits of the syrphids did not sufficiently explain syrphid occurrence at the sites. Possible explanations are discussed and an outlook for further studies is given. 1. Introduction The first use of organisms as indicators for environmental conditions dates back to the days of Aristotle, who placed freshwater fish in salt water to observe their reactions (CAIRNS and PRATT, 1993). Farmers have used plants as bioindicators for thousands of years (DIEK- MANN, 2003). The medieval King’s wine tasters or the canaries used to indicate air quality in coal mines are other historical examples for bioindicators (BURRELL and SIEBERT, 1916; CAIRNS and PRATT, 1993). Bioindicators can thus be defined as living organisms indicating environmental conditions through their presence or abundance (DZIOCK et al., 2006). The past 40 years have seen a rapid development of ideas, concepts, and application of bioindicators (for reviews see METCALFE, 1989; CAIRNS and PRATT, 1993; MCGEOCH, 1998; NIEMI and MCDONALD, 2004). Currently, there is a strong need for reliable environmental assess- ment procedures because of environmental policies (e.g. the EU Habitat Directive) concen- trating on cost-efficiency and applicability of bioindication systems on a large scale (at least pan-European). One potential way of achieving this would be to use general biological traits of organisms that indicate ecological functions (STATZNER et al., 2001a). These traits are used to reveal functional relationships of the species to habitat selective forces. These forces can be viewed as filters occuring at different spatial scales. To join a local community, species must pos- sess appropriate functional attributes (species traits) to pass through the habitat filter (SOUTH- WOOD, 1977, 1996). Such traits and their relationships to the filter (environmental conditions) are considered to hold on a geographical scale and thus have potentially broad generality (POFF, 1997; STATZNER et al., 2001b). By contrast, applied ecologists often describe © 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 1434-2944/06/408-341 342 F. DZIOCK or predict patterns of distribution and abundance without reference to biological mecha- nisms. These correlative approaches are of uncertain generality. Including biological infor- mation may make their predictions more robust and generalizable (POFF, 1997). This is because in different biogeographical regions or in the same region but in a different ecosys- tem, different species might be involved occupying the same functional niche. This transferability in space is augmented by a potential transferability in time. The problems caused by limited trap exposition time and seasonal differences in species occurrence could also be overcome by using species biological traits instead of species occurrence or abundance alone. Using species traits to characterise community composition in terrestrial invertebrates has been largely univariate in approach, i.e., restricted to analysis of single or a few traits (e.g. HODGSON, 1993; PURTAUF et al., 2005; but compare CASTELLA and SPEIGHT, 1996). However, using many traits simultaneously enhances the understanding of how species composition will change as environmental constraints vary across the landscape (POFF, 1997; STATZNER et al., 2001b). Although this multi-trait approach to understanding the relationship between life history and environment has been followed in numerous studies in stream ecology (e.g. POFF, 1997; STATZNER et al., 1997, 2004; USSEGLIO-POLATERA et al., 2000; GAYRAUD et al., 2003), its potential in terrestrial ecosystems, especially for terrestrial invertebrates remains largely unexplored. The family Syrphidae is among the most diverse Diptera groups as regards larval biolo- gy and habitat preferences (THOMPSON and ROTHERAY, 1998). Hoverflies can be found in almost every terrestrial and many aquatic habitats. The adults are important pollinators and use only pollen, nectar, and occasionally honey dew as food resources. In contrast, the larvae show an amazing variety of life styles. They live on decaying wood, sap from sapruns on trees, fungi, living or rotting plants, dung, muddy water, aphids, ant eggs, larvae and pupae, or other insects (THOMPSON and ROTHERAY, 1998). One species in Central Europe (Volucella inanis) is even a true parasitoid of wasp larvae (RUPP, 1989). Their spectrum of life history strategies in floodplains also shows a high diversity. Most species are dependent on more than one habitat type, because larval and adult habitats differ from one another. Larvae are restricted to their larval substrate, whereas the emerging adults visit flowers and move around between different biotope types (SSYMANK, 2001). Because larvae are much more specialized than the adults in their feeding preferences, they often play a key role in syrphid species distribution. Syrphid flies have not often been used in bioindication processes, despite their large potential in this respect. This is mainly due to some difficulties concerning the determination of the species arising from the fact that there is no determination book available that covers the whole range of species occurring in Europe (ca. 800 species) or even Central Europe (ca. 550 species). However, very recently a determination book has been published (VAN VEEN, 2004) that covers the whole of Northern Europe with large parts of Western and Central Europe, but excludes the mediterranean and mountainous areas (e.g. the Alps). Another problem was the availability of life history traits data, which is scattered in numerous not-easy-to-obtain publications, often in difficult-to-translate languages. A lot of these data have been collated in the publication by BARKEMEYER (1994). A database with a large amount of data on habitat preferences and some data on life history traits has been compiled by SPEIGHT et al. (2004). This study endeavours to take advantage of these data and aims at testing the use of hoverflies for bioindication in floodplain grasslands while incorporating life history traits data in the analysis process. We aim to answer two questions: – Do syrphid species respond to small scale changes in environmental variables (e.g. groundwater depth, cation exchange capacity etc.) in seasonally flooded grasslands in the Elbe floodplain? © 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.revhydro.com Hoverflies as Bioindicators 343 – Can species response to environmental variables be explained by the biological characteristics of the species expressed by their multiple life history traits as coded in the database Syrph the Net (SPEIGHT et al., 1998)? This is the first study to analyse syrphid species response to environmental variables and simultaneously incorporate life history data on the syrphid species into the statistical approach. 2. Methods The 15 study sites are situated in Central Germany in the Elbe floodplain (Land Saxony-Anhalt). The study area is part of the UNESCO biosphere reserve “River Elbe Landscape” (SCHOLZ et al., 2005). All study sites can be characterised as open grassland areas which are seasonally flooded. They had been chosen in the course of the “RIVA”-project (HENLE et al., 2006). We carried out a stratified systematic random sampling design (SNEDECOR and COCHRAN, 1980; WILDI, 1986). For more details on the study area see HENLE et al. (2006). A phyto-sociological characterisation of the study sites is given in Table 1. Table 1. Study sites in the Elbe floodplain, where syrphids were surveyed. Study area Biotope characteristics Site no. Steckby Eleocharietum palustris, Ranunculo repentis-Alopecuretum 4 geniculati, Phalaridetum arundinaceae Steckby Potentillion anserinae, Bidenti-Polygonetum hydropiperis 9 Steckby Agropyretum repentis, Phalaridetum arundinaceae, 10 Rumici crispi-Agrostietum stoloniferae Steckby Galio molluginis-Alopecuretum pratensis 20 Steckby Galio molluginis-Alopecuretum pratensis 21 Steckby Dauco carotae-Arrhenateretum elatioris 26 Steckby Sanguisorbo officinalis-Silaetum silai 29 Steckby Sanguisorbo officinalis-Silaetum silai 30 Steckby Sanguisorbo officinalis-Silaetum silai 34 Wörlitz Glycerietum maximae, Bidention tripartitae 39 Wörlitz Glycerietum maximae, Caricetum gracilis 40 Wörlitz Galio molluginis-Alopecuretum pratensis 42 Sandau Rumici crispi-Agrostietum stoloniferae, Rorippo-Oenanthetum 51 aquaticae, Bidenti-Polygonetum hydropiperis Sandau Phalaridetum

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