Cross-Taxon Congruence of Species Diversity and Community Similarity Among Three Insect Taxa in a Mosaic Landscape

BIOLOGICAL CONSERVATION Biological Conservation 126 (2005) 195–205 www.elsevier.com/locate/biocon Cross-taxon congruence of species diversity and community similarity among three insect taxa in a mosaic landscape Sabine Oertli, Andreas Mu¨ller *, Dominik Steiner, Alexandra Breitenstein, Silvia Dorn Institute of Plant Sciences/Applied Entomology, Swiss Federal Institute of Technology (ETH), Clausiusstr. 25, CH-8092 Zurich, Switzerland Received 9 November 2004; received in revised form 19 April 2005; accepted 8 May 2005 Abstract Surrogate taxa as indicators for biodiversity are widely used in conservation biology and ecology. However, available studies on the congruence of species diversity patterns in different taxa yielded inconsistent results, and correlations between taxa were few. To conserve or restore biodiversity in agricultural landscapes, knowledge on the response of different taxa to management regimes is crucial. In the present study we evaluated the congruence of diversity and similarity patterns among three insect taxa, i.e., bees, grasshoppers, and aculeate wasps, in a mosaic landscape in the Swiss Alps comprising extensively used grassland under different management regimes. In addition, we studied the influence of land use on the diversity and species composition of the three taxa. While species numbers were not significantly correlated between any pair of taxa, community similarities were positively correlated between bees and grasshoppers. The number of red-listed species was not correlated with the total number of species in bees and in grasshoppers. None of the investigated taxa reflected the species numbers or community similarities of the other taxa well enough to qualify as a general indicator for biodiversity. Remarkably, land use clearly influenced species composition, while its effect on species numbers was not significant. All management regimes of the grassland in the study area contribute substantially to the overall diversity of the three insect taxa. Conserving the variety of agricultural land uses will be the most promising step towards the conservation of biodiversity in the study area. Ó 2005 Elsevier Ltd. All rights reserved. Keywords: Biodiversity indicators; Insects; Community similarity; Species richness; Mosaic landscape 1. Introduction uated the congruence of species diversity among poten- tial taxa, however, with inconsistent results (Prendergast Measuring and monitoring biodiversity is an essential et al., 1993; Weaver, 1995; Baur et al., 1996; Prender- tool for the selection of nature reserves and the evalua- gast, 1997; Duelli and Obrist, 1998; Howard, 1998; Pa¨rt tion of management regimes aiming at the conservation and So¨derstro¨m, 1999; Negi and Gadgil, 2002; Ricketts or restoration of biodiversity. As assessing the complete et al., 2002; Schwab et al., 2002; Vessby et al., 2002; Car- biodiversity is impossible, the use of surrogate measures doso et al., 2004; Kati et al., 2004; Sauberer et al., 2004; has become widespread. Groups of organisms defined at Su et al., 2004; Summerville et al., 2004; Heilmann-Clau- different taxonomic levels are suggested as indicators for sen and Christensen, 2005; Saetersdal et al., 2005). biodiversity (Noss, 1990; McGeoch, 1998). However, Mere species numbers can easily be communicated to their use is only valid if their species numbers are corre- non-specialists such as decision makers. However, they lated with the diversity of other taxa. A growing number do not provide sufficient information for conservation of studies from various habitats and spatial scales eval- purposes where habitat requirements, phylogenetic position or conservation status of organisms are of * Corresponding author. Tel.: +41 1 632 3908; fax: +41 1 632 1171. major interest (Huston, 1994). Only few investigations E-mail address: [email protected] (A. Mu¨ller). into the congruence of different indicator taxa analysed 0006-3207/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.biocon.2005.05.014 196 S. Oertli et al. / Biological Conservation 126 (2005) 195–205 species composition, and the results do not clarify and landscape diversity on bees revealed land use as the whether the use of indicator taxa is more successful at most important factor for bee community structure the level of species composition than of species numbers (Oertli et al., unpublished). As land use is of outmost sig- (Howard, 1998; Negi and Gadgil, 2002; Vessby et al., nificance for conservation measures in agricultural land- 2002; Su et al., 2004). scapes, the current study is focused on the effects of land Mechanization and intensification of agriculture have use on diversity and community composition. Results lead to a decrease in biodiversity in most agricultural are discussed regarding the use of bees, grasshoppers landscapes during the past decades (Chamberlain and aculeate wasps as indicators for overall species diver- et al., 2000; Benton et al., 2002). Therefore, conservation sity, and regarding the significance of the present man- biology in such areas is focused mainly on the elabora- agement regimes for the species diversity in the area. tion and evaluation of management regimes which reduce the loss of biodiversity or restore it on agricultural land. However, some of these agri-environmental 2. Methods schemes did not enhance biodiversity to the expected de- gree (Kleijn et al., 2001; Kleijn and Sutherland, 2003; 2.1. Study area and investigated taxa Kleijn et al., 2004). Hence, a prerequisite for the preven- tion of biodiversity loss is to understand the effect of The study was carried out on the southern slope of management on different taxa and to anticipate the ef- the Valais (Switzerland) in an area of approximately fects of land use changes in agroecosystems with a high 2km2 around the village of Erschmatt (46°1901800N/ biodiversity. Effective conservation of biodiversity re- 7°4103000E) at an altitude of 1150–1550 m above sea le- quires consideration of the ecological demands of differ- vel. The climate is characterized by low precipitation, ent taxa in management strategies (WallisDeVries et al., especially during the growing season, and by high evap- 2002). To date, focus in agricultural landscapes has of- oration. Inclination of the study area ranges between ten been set on plant diversity, which, however, does south and south-west. The underlying rocks of lime- not always reflect the diversity of other organisms (Pa¨rt stone are covered by glacial sediments deficient in lime and So¨derstro¨m, 1999; Kruess and Tscharntke, 2002a). and with a varying content of sand and clay. The area Furthermore, different groups of animals may react dif- consists of a mosaic of different grassland types with ferently to management or disturbance (Lawton et al., interspersed rocky areas, forests and groves (Fig. 1). 1998; Wettstein and Schmid, 1999; Perfecto et al., The main vegetation types are Arrhenatherion, Mesob- 2003; Kleijn et al., 2004). romion, Stipo-Poion, Sedo-Scleranthion, and Onon- In the montane areas of Switzerland, land use has ido-Pinion (Delarze et al., 1999). The study area until recently been relatively extensive. Due to the heter- harbours an exceptionally high biodiversity, and the ogeneous topography and a variety of different manage- bee fauna was shown to be one of the richest in Central ment regimes, montane landscapes often consist of a Europe (Oertli et al., 2005). Within the study area, seven mosaic of different habitats which are rich in species categories of land use were defined. Two different types compared to the intensively used agroecosystems in of hay meadows of two cuts were distinguished. They the lowlands. The open grassland habitats, except for differed in landscape context with one lying in a mosaic the steppic grassland which is very nutrient poor, were of different land use types, and the other forming part of all created by human land use. However, agricultural a large hay meadow of two cuts. The third category in- landscapes in the Alps are under growing economic cluded hay meadows of one cut. Two types of pastures pressure with two possible consequences: areas which were included, one which was grazed by sheep in spring are not easily accessible are abandoned and are over- and autumn, and another which was grazed by Scottish grown by bushes and trees, while land use is intensified Highland cattle for a few weeks, once or twice between in other areas by increasing application of fertilizers, May and September. Finally, two categories of non- more frequent cutting or increased numbers of livestock agriculturally used grassland were included. One was (MacDonald et al., 2000). Both directions of change will dry grassland abandoned for several decades following lead to a decrease in biodiversity in the long term. its previous use as grain fields. The other was steppic The present study was performed in a montane grass- grassland with open rock surfaces. For each of the seven land ecosystem comprising a variety of management re- land use categories four permanent study plots of gimes to: (1) test the congruence of species numbers 1600 m2 each were marked out in the field resulting in and species composition among three insect taxa, bees, 28 study plots (Fig. 1). grasshoppers, and aculeate wasps, at a local scale, and The three insect taxa investigated in this study repre- (2) to compare the influence of land use on the patterns sent different biological characteristics: Bees have high of species numbers and species composition of all three and species-dependent requirements for flowering plants taxa. In the same study area, a detailed investigation into as a nutritional source for adults and their progeny, and the relative importance of land use, resource abundance, for nesting sites (Westrich, 1990; Mu¨ller, 1996; Wcislo S. Oertli et al. / Biological Conservation 126 (2005) 195–205 197 Fig. 1. Study area on a south-exposed slope with habitat types and location of the study plots. and Cane, 1996; Mu¨ller and Kuhlmann, 2003). Bees are duration was one hour per period and plot.

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