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. The bees considered as highly mobile, switching between different were killed and determined to the species level. partial habitats. Grasshoppers are relatively unspecial- Grasshoppers were assessed along a transect of ized herbivores or herbi-/carnivores which are rather 100 m, which was laid through each plot, crossing sedentary (Detzel, 1998). Vegetation structure, microcli- all major structures present on the plot. The transects mate, and soil characteristics are factors which influence were walked during one hour per plot, twice between the distribution of grasshopper species. Aculeate wasps mid-July and mid-September 2002. Singing grasshop- resemble bees regarding requirements for nesting sites per species were recorded based on the species-specific (Witt, 1998) but differ regarding nutrition. While adults songs of the males. Non-singing species and those rely on nectar sources, larvae are carnivorous, hence, the using ultrasound were visually assessed. All grasshop- distribution of prey is an important aspect for aculeate per individuals were recorded in front of the investiga- wasps. tor, one metre to the left and to the right of the transect. As only males sing (Detzel, 1998), counts 2.2. Sampling methods of mute species were divided by two to correct for the sex-ratio, which was shown to be close to one in All insects were only sampled on warm and sunny preliminary investigations. After each transect walk, days with little or no wind. the whole plot was searched for undetected species Bees were collected by means of direct netting during during 10 min. These additional species were given five sampling periods per year from April to August the value one, and all counts from the transect were 2001 and from May to September 2002. Sampling enlarged by one. 198 S. Oertli et al. / Biological Conservation 126 (2005) 195–205

The wasp families Sphecidae, Chrysididae, Pompili- three matrices of similarity were analysed by a Mantel dae and Vespidae were sampled by direct netting during test for correlation between pairs of the three indica- a total of three sampling periods in June, July and Au- tor taxa. The species composition was characterized gust 2003. Sampling duration was one hour per plot by means of Correspondence Analysis (CA). and period. All specimens were killed and determined The influence of land use on the species numbers per to the species level. plot was analysed by means of Kruskal–Wallis tests fol- The data sampling for the present study extended lowed by a Nemenyi post hoc test for pairwise compar- over three years. Habitat characteristics of the peren- isons (Zar, 1999). Canonical Correspondence Analysis nial grassland did not change during the course of (CCA) followed by Monte-Carlo permutation with 999 the study (S. Oertli, pers. obs.). The sampling periods randomizations was used to test the influence of land for bees (2001/2002) and grasshoppers (2002) over- use type on species composition. lapped. A detailed analysis of the bee data revealed Multivariate analyses (CA and CCA) were performed that the species numbers per plot and the community on Canoco 4.5 (ter Braak and Smilauer, 2002). Rare and similarities between pairs of plots correlated well very frequent species were excluded to reduce the noise between the two years (detailed under ÔStatistical in the data sets. The decision for the limits of exclusion AnalysisÕ). Aculeate wasps were sampled during the was taken for each taxon separately by performing Cor- subsequent summer (2003) which was warmer and respondence Analyses in which species occurring on a drier than the preceeding two summers, what might certain number of plots were subsequently excluded. have modified the detailed data. However, we believe Based on the results of these analyses, limits were set that the general patterns of species numbers and com- where the relation was optimal between the reduction munity composition documented and discussed in this of total inertia (reflecting noise) and the loss of informa- paper are valid, and that the methods used are suit- tion expressed by the eigenvalue of the first ordination able for the purpose of this study. axis. Thus, bee species occurring on less than three (n = 66) or more than 25 (n = 4) plots were excluded, 2.3. Statistical analyses as well as grasshopper species occurring on only one plot (n = 4), and wasp species occurring on less than The data of all sampling periods were pooled for three plots (n = 68). each plot prior to data analysis. The bee data of The indicator value method (Dufreˆne and Legen- 2001 and 2002 were pooled as species numbers per dre, 1997) was used to identify species which were plot and community similarities between pairs of plots characteristic for one of the seven investigated land were significantly correlated between the two years use types and might thus suffer most through the loss (SpearmanÕs q = 0.502, p = 0.007; Mantel r = 0.640, of a land use type. The indicator value (IndVal) com- p < 0.001). The significance level for all statistical tests bines the specificity of a species and its fidelity. In our was 5%. study, specificity was at its maximum when a species The congruence of species richness between the occurred only in one of the seven land use types, three taxa was tested by pairwise Spearman rank cor- and fidelity was at its maximum when the species oc- relation tests using the mean number of species per curred on all four plots of a land use type. When both plot for each of the seven land use types. Analyses values are at their maximum, the indicator value is at the level of species numbers were performed for 100. the mean number of all species and for the mean number of red-listed species in bees and grasshoppers. Information on the red-listed species was extracted 3. Results from Amiet (1994) for bees, and from Thorens and Nadig (1997) for grasshoppers. In Switzerland, no We collected and identified a total of 5129 bee indi- Red List exists for aculeate wasps to date. As most viduals in 215 species, 5578 grasshopper individuals in species recorded in this study are listed in the category 29 species, and 459 wasp individuals in 98 species during ÔendangeredÕ, no further differentiation of conservation this study. Species recorded with one individual only value was made in the analyses. (singletons) made up 16.3% of all bee species, 6.9% of For the analysis of congruence at the level of spe- all grasshopper species, and 38.8% of all aculeate wasp cies composition, data of the four plots of each land species. use types were pooled, and the Bray–Curtis index of Of the 215 bee species 34.0% are registered in the na- similarities between all possible pairs of land use types tional Red List, and of the 29 grasshopper species was calculated for each taxon. The Bray–Curtis index, 55.2%. presented as ÔSorenson quantitative indexÕ in Magur- The number of species per plot ranged from 36 to 72 ran (1988), includes not only the mere presence of spe- for bees, from 9 to 19 for grasshoppers, and from 1 to 25 cies in the calculation but also their abundance. The for aculeate wasps. S. Oertli et al. / Biological Conservation 126 (2005) 195–205 199

3.1. Cross-taxon congruence of species numbers and a p = 0.001 species composition 1

0. 8 The mean species numbers per land use type were not significantly correlated between any pair of taxa (bees 0. 6 versus grasshoppers: n =7;q = 0.321, p = 0.482; bees versus aculeate wasps: n =7;q = 0.252, p = 0.585; grass- similarity 0. 4 hoppers versus aculeate wasps: n =7; q = 0.468, p = 0.289). The mean number of red-listed species was Grasshopper community 0. 2 correlated with the mean total number of species neither in bees nor in grasshoppers (bees: n =7; q = 0.679; 0 p = 0.094; grasshoppers: n =7;q = 0.393; p = 0.383). 00.20.40.60.81 The numbers of red-listed species of grasshoppers and Bee community similarity bees were not significantly correlated (n =7; q = 0.036; p = 0.939). b 1 p = 0.226 Community similarities obtained from the Bray–Cur- tis index were significantly correlated between bees and 0. 8 grasshoppers (n = 21; Mantel r = 0.900, p = 0.001; Fig. 2(a)). Thus, pairs of plots with similar bee assem- 0. 6 blages also had similar grasshopper assemblages. The community similarities in bees and aculeate wasps were 0. 4 not significantly correlated (n = 21; Mantel r = 0.181, Aculeate wasp community similarity p = 0.226; Fig. 2(b)), nor were the community similari- 0. 2 ties in grasshoppers and aculeate wasps (n = 21; Mantel r = 0.061, p = 0.415; Fig. 2(c)). 0 In bees and grasshoppers, the patterns of species 0 0.2 0. 4 0.6 0. 8 1 composition revealed by Correspondence Analysis Bee community similarity were characterized by a gradual change along the first ordination axis from meadows over pastures and fal- c 1 p = 0.415 low land to steppic grassland (Fig. 3). In aculeate wasps, the plots of none of the land use types were 0.8 clustered together. 0.6 3.2. Influence of land use on diversity and species composition 0.4 Aculeate wasp

The number of species per plot was not significantly community similarity 0.2 different between land use types in any of the three in- 0 sect taxa (Kruskal–Wallis test; bees: H6 = 7.38, 0 0.2 0.4 0.6 0.8 1 p = 0.287; grasshoppers: H6 = 8.90, p = 0.179; aculeate Grasshopper community similarity wasps: H6 = 8.44, p = 0.208). The number of species per plot was highly variable within the land use types Fig. 2. Cross-taxon correlations among community similarity (Bray– in bees and aculeate wasps but less so in grasshoppers Curtis index) in bees, grasshoppers, and aculeate wasps between all 21 (Fig. 4). pair-wise combinations of land use types. Species composition differed significantly between land use types in all three taxa (Canonical Correspon- dence Analysis; bees: p = 0.001; grasshoppers: p = Significant values were observed in 24 bee species 0.001; aculeate wasps: p = 0.011). Land use explained (11.2% of all bee species), 16 grasshopper species 38.6% of the variance in the bee data, 67.4% of the var- (55.2%), and five aculeate wasp species (5.1%) (Table iance in the grasshopper data, and 28.9% of the variance 1). Seven of the 24 bee species (29%) and eight of in the wasp data. Thus, the influence of land use on the the 16 grasshopper species (50%) with a significant species composition was strongest in grasshoppers and indicator value are registered in the national Red List. weakest in aculeate wasps. While red-listed bee species were observed on nearly The average indicator value for all species was all land use types, red-listed grasshopper species were highest in grasshoppers (40.39 ± 3.24), followed by only observed on the pastures, fallow land and steppic bees (28.96 ± 1.06) and aculeate wasps (23.78 ± 1.07). grassland. 200 S. Oertli et al. / Biological Conservation 126 (2005) 195–205

a b CUT2M CUT2M CUT2H CUT2H 3.0 CUT1 3.0 CUT1 SHEEP SHEEP CATTLE CATTLE FALLOW FALLOW STEPPIC STEPPIC

-2.0 2.0 -2.0 2.0

-2.0 -2.0

c CUT2M CUT2H 3.0 CUT1 SHEEP CATTLE FALLOW STEPPIC

-2.0 2.0

-2.0

Fig. 3. Ordination diagrams showing the study plots along the ﬁrst two axes obtained from Correspondence Analysis of (a) bees, (b) grasshoppers, and (c) aculeate wasps. The ﬁrst two axes account for 23.5% of the variance in bees, 53.3% in grasshoppers, and 18.8% in aculeate wasps. CUT2M, meadows of two cuts lying in a mosaic; CUT2H, meadows of two cuts lying in a large meadow; CUT1, meadows of one cut; SHEEP, sheep pastures; CATTLE, cattle pastures; FALLOW, fallow land; STEPPIC, steppic grassland.

4. Discussion numbers among all three taxa were not to be expected at the small spatial scale of our study area, and there 4.1. Cross-taxon congruence are no indications for further gradients that aﬀect species numbers per plot. Species numbers of bees and acu- Patterns of species richness were not congruent be- leate wasps, as representatives of aculeate Hymenoptera, tween the three insect taxa studied, i.e., bees, grasshop- showed no congruence with each other or with grass- pers, and aculeate wasps. These results support further hoppers. In contrast, the species numbers of aculeate studies which revealed poor congruence between species Hymenoptera (including wasps and bees) were shown numbers of diﬀerent taxa (Weaver, 1995; Niemela¨ and to be good indicators for the total number of species Baur, 1998; Oliver et al., 1998; Vessby et al., 2002; Per- recorded in an agricultural landscape (Duelli and Obrist, fecto et al., 2003; Su et al., 2004). Climatic or biogeo- 1998). All aculeate Hymenoptera together might be graphic gradients favouring a congruence of species better indicators for species diversity than taxa at lower S. Oertli et al. / Biological Conservation 126 (2005) 195–205 201

a 80 among plants, birds, and butterflies in mountain mea- 70 dow habitats (Su et al., 2004), and similar biogeo- graphic patterns caused congruent community 60 similarities among woody plants, large moths, butter- 50 flies, and birds in different forest habitats in Uganda 40 (Howard, 1998). In contrast, community similarities 30 of only few taxa were correlated in Swedish grassland 20 habitats (Vessby et al., 2002) due to different re- 10 sponses of the studied taxa to habitat characteristics 0 such as vegetation heterogeneity or percentage of

shrubs. Hence, congruence of community similarities

CUT1 at local or regional scales may only be observed if a CUT2H SHEEP CUT2M

CATTLE strong environmental gradient is present, and if the FALLOW FALLOW STEPPIC studied taxa respond to the gradient in a similar b 20 way. The strong congruence of community similarities between bees and grasshoppers was a surprising out- 15 come of the present study. Land use was identified as the dominant driving force that caused a gradual change of species composition from hay meadows 10 over pastures and fallow land to steppic grassland in the two taxa. However, the mechanisms underlying 5 the common response of bees and grasshoppers must be different. While grasshoppers are known to be 0 strongly influenced by vegetation structure, microclimate and soil characteristics (Detzel, 1998), bee com-

CUT1 munities are structured by the abundance and CUT2H SHEEP SHEEP CUT2M CATTLE

FALLOW distribution of pollen sources and nesting sites (Wes- STEPPIC trich, 1990; Westrich, 1996; Oertli et al., unpublished). c 25 Further investigations will have to evaluate to which extent the environmental factors structuring bee and 20 grasshopper communities are also intercorrelated in 15 other habitats and under different management regimes. Community similarities of aculeate wasps were 10 not significantly correlated with those of bees and grasshoppers. The biological requirements of aculeate 5 wasps are the most complex among the three insect 0 taxa included in this study (Witt, 1998). Hence, a sin- gle environmental factor, such as land use, may not be sufficient to explain the community structure of acule- CUT1 CUT2H SHEEP SHEEP CUT2M ate wasps. CATTLE FALLOW STEPPIC Both, areas of high total species diversity and areas Fig. 4. Highest and lowest number of species observed per plot (boxes) that harbour a high number of threatened species are and mean value (dash) in the seven different land use types for (a) bees, of major interest for conservation, but they often do (b) grasshoppers, and (c) aculeate wasps. Scales of the value axes are not coincide. Our study provides further evidence to this different between the taxa. CUT2M, meadows of two cuts lying in a mosaic; CUT2H, meadows of two cuts lying in a large meadow; differentiated view. Furthermore, the mean number of CUT1, meadows of one cut; SHEEP, sheep pastures; CATTLE, cattle red-listed species were not correlated between bees and pastures; FALLOW, fallow land; STEPPIC, steppic grassland. grasshoppers. Thus, conserving the variety of different land use types in the study area may allow for the conservation of both areas with many threatened species systematic levels, because the higher level integrates a and areas with a high total species richness. variety of ecological guilds including herbivores, preda- tors, and parasitoids. 4.2. Influence of land use In bees and grasshoppers, the community similarities were stronger in contrast to the species numbers. Land use type did not significantly influence the spe- A strong hydrological gradient was identified as the cies numbers of any of the three indicator taxa. The data driving force for congruent community similarities were characterized by a high variation within land use 202 S. Oertli et al. / Biological Conservation 126 (2005) 195–205

Table 1 Bee, grasshopper, and aculeate wasp species with a signiﬁcant indicator value Indicated land use typea IndVal N Bees Andrena thoracica CUT2Mb 75.00 4 Lasioglossum nigripes CUT2M 56.00 10 Melitta haemorrhoidalis CUT2M 55.10 49 Andrena proxima CUT2M 55.06 89 Andrena humilis CUT2M 54.17 24 Lasioglossum zonulum CUT2M 50.00 18 Andrena tibialis CUT2M 50.00 6 Andrena haemorrhoa CUT2M 44.55 101 Halictus simplex CUT2M 30.74 579 Heriades truncorum CUT2Hb 100.00 7 Bombus hortorum CUT2H 57.14 14 Lasioglossum laevigatum CUT2H 51.02 49 Lasioglossum subfasciatum CUT2H 50.00 16 Lasioglossum costulatum CUT1 41.67 9 Panurgus banksianus CUT1 41.32 121 Osmia claviventris SHEEPb 100.00 7 Dufourea minuta SHEEP 64.77 22 Melitta tricincta SHEEP 64.29 28 Bombus lapidarius SHEEP 37.58 149 Sphecodes geofrellus CATTLEb 75.00 8 Megachile analis CATTLE 50.00 22 Anthophora aestivalis CATTLE 36.11 36 Lasioglossum lissonotum STEPPICb 75.00 5 Megachile melanopyga STEPPIC 61.36 11

Grasshoppers Metrioptera roeseli CUT2M 50.00 46 Chorthippus biguttulus CUT2M 39.31 290 Pholidoptera griseoaptera CUT2H 50.00 18 Arcyptera fusca CUT2H 45.96 161 Chorthippus dorsatus CUT2H 45.19 385 Chorthippus parallelus CUT2H 39.26 894 Psophus stridulus SHEEP 89.47 19 Decticus verrucivorus CATTLE 46.43 28 Omocestus haemorrhoidalis CATTLE 35.82 335 Stauroderus scalaris CATTLE 30.22 986 Oecanthus pellucens FALLOW 53.61 97 Calliptamus italicus STEPPIC 89.39 66 Oedipoda germanica STEPPIC 56.76 37 Chorthippus brunneus STEPPIC 56.16 73 Chorthippus vagans STEPPIC 45.31 96 Platycleis albopunctata STEPPIC 42.16 287

Aculeate waspsc Arachnospila trivialis SHEEP 50.00 9 Podalonia affinis CATTLE 50.00 9 Ammophila apicalis CATTLE 43.75 12 Eumenes pomiformis FALLOW 53.57 7 Polistes dominulus FALLOW 46.67 135 For each species, the indicated land use type, indicator value (IndVal) and number of observed individuals (N) are given. Red-listed species are printed in bold. a CUT2M, meadows of two cuts lying in a mosaic; CUT2H, meadows of two cuts lying in a large meadow; CUT1, meadows of one cut; SHEEP, sheep pastures; CATTLE, cattle pastures; FALLOW, fallow land; STEPPIC, steppic grassland. b Species only observed on the indicated land use type. c No Red List available for Switzerland. S. Oertli et al. / Biological Conservation 126 (2005) 195–205 203 types in the bee and wasp data, while species numbers land use influenced bee and grasshopper community were similar between the different land use types in the composition in a similar way, bees were less strongly grasshopper data. The power of the Kruskal–Wallis test associated with certain land use types. When bees have was limited due to the relatively low number of repli- to move between different habitats to find all required cates. However, we suggest that a higher number of rep- resources, their association with particular land use licates would not change the results, as the data within types will be weaker. The same need may prevent a taxa overlap widely between land use types. The species strong association of aculeate wasps with land use types. number of trap-nesting bees was not significantly Hence, the underlying complex biological requirements influenced by different management types in orchard of the two hymenopteran taxa suggest that they may meadows (Steffan-Dewenter and Leschke, 2003). In con- be threatened as seriously as grasshoppers by the loss trast, trap-nesting bees and aculeate wasps had signifi- of a distinct land use type. As the partial habitats re- cantly higher species numbers on grazed than on quired by bees and aculeate wasps usually provide ungrazed grassland (Kruess and Tscharntke, 2002b), non-substitutable resources such as pollen and nesting and species numbers of trap-nesting bees were higher sites, even the loss of one land use type may interrupt on set-aside fields than on crop fields (Gathmann the life cycle of some bee or aculeate wasp species. et al., 1994). Grazed montane wetlands in Switzerland showed significantly higher species numbers of grass- 4.3. Implications for conservation hoppers than mown wetlands (Wettstein and Schmid, 1999), while a weakly negative effect of increased grazing Species numbers and species composition represent intensity on the species numbers was shown for grass- different aspects of biodiversity and should both be ana- hoppers on grasslands in Northern Germany (Kruess lysed in biodiversity studies. The lack of congruence in and Tscharntke, 2002b). Thus, the effect of land use patterns of species richness in the three studied taxa sug- on species diversity depends on the type of management gests that conservation measures have to be elaborated investigated and on the range of the disturbance gradi- individually for each taxon. Similarly, targeting conser- ent included in the study. In the current study, the dis- vation measures merely at the total number of species turbance gradient was limited, ranging from no may not prevent red-listed species from going extinct. disturbance in steppic grassland and fallow to moderate The investigated insect taxa did not prove to be good disturbance in hay meadows cut twice. We suggest that indicators for biodiversity at a local scale in a heteroge- the disturbance gradient in the research area is too small neous landscape. Assessing diversity patterns of a selec- to reveal significant effects of land use on species diver- tion of taxa may allow for the identification of the major sity in all three investigated taxa. driving forces for biodiversity, which then can be used to In contrast to species numbers, community composi- elaborate conservation measures. The small-scale mo- tion was strongly influenced by land use in all three indi- saic of different land use types is a key characteristic cator taxa, an effect which is important for the of the study area and was shown to be responsible for conservation of biodiversity. The fact that a similar the total species diversity observed in all three investi- number of species was found in different land use types gated taxa. Thus, conserving the variety of agricultural does not exclude the possibility that the loss of a type land uses will be the most promising step towards the may have consequences for species diversity. 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