Life in harsh environments: carabid and spider trait types and functional diversity on a debris‐covered glacier and along its foreland

1. Patterns of species richness and species assemblage composition of ground‐dwelling arthropods in primary successions along glacier forelands are traditionally described using a taxonomic approach. On the other hand, the functional trait approach could ensure a better characterisation of their colonisation strategies in these types of habitat. 2. The functional trait approach was applied to investigate patterns of functional diversity and life‐history traits of ground beetles and spiders on an alpine debris‐covered glacier and along its forefield in order to describe their colonisation strategies. 3. Ground beetles and spiders were sampled at different successional stages, representing five stages of deglaciation. 4. The results show that the studied glacier hosts ground beetle and spider assemblages that are mainly characterised by the following traits: walking colonisers, ground hunters and small‐sized species. These traits are typical of species living in cold, wet, and gravelly habitats. The diversity of functional traits in spiders increased along the succession, and in both carabids and spiders, life‐history traits follow the ‘addition and persistence model’. Accordingly, there is no turnover but there is an addition of new traits and a variation in their proportion within each species assemblage along the succession. The distribution of ground beetles and spiders along the glacier foreland and on the glacier seems to be driven by dispersal ability and foraging strategy. 5. The proposed functional approach improves knowledge of the adaptive strategies of ground‐dwelling arthropods colonising glacier surfaces and recently deglaciated terrains, which represent landforms quickly changing due to global warming.     

Invasive moss alters patterns in life-history traits and functional diversity of spiders and carabids

Invasive plants can modify terrestrial habitats and affect the natural faunal composition. In acidic coastal dunes the invasive moss Campylopus introflexus can form dense carpets that largely replace native vegetation. As shown in a previous study, moss invasion affects habitat structure and ground-dwelling arthropod diversity. We suggested that including the functional diversity concept in the analysis of moss invasion impacts may offer further insights. We used pitfall trap data to compare trait composition and functional diversity of spiders and carabids in (a) invaded, moss-rich (C. introflexus) and (b) native, lichen-rich (Cladonia spp.) acidic coastal dunes. Moss invasion induced shifts in the trait values body size and feeding preference (carabids) and hunting mode (spiders): Species were smaller in native sites, and the percentages of web-building spiders and phytophagous beetles were reduced in invaded sites. Furthermore, moss invasion led to a more heterogeneous trait composition for spiders, and changed functional diversity of both arthropod groups, although with the opposite effects: While spiders were functionally more diverse in invaded sites, moss invasion reduced carabid beetles’ functional diversity. We also observed changes in the relationship between species richness and functional diversity that indicate a high functional similarity for spiders but a lower one for carabid beetles in native grey dunes. C. introflexus invasion not only alters the arthropod diversity and assemblage structure of endangered acidic coastal dunes but also interferes at a functional level. These results provide further insight into the way plant invasions might alter the structure and function of ecosystems.     

Even the Smallest Non-Crop Habitat Islands Could Be Beneficial: Distribution of Carabid Beetles and Spiders in Agricultural Landscape

Carabid beetles and ground-dwelling spiders inhabiting agroecosystems are beneficial organisms with a potential to control pest species. Intensification of agricultural management and reduction of areas covered by non-crop vegetation during recent decades in some areas has led to many potentially serious environmental problems including a decline in the diversity and abundance of beneficial arthropods in agricultural landscapes. This study investigated carabid beetle and spider assemblages in non-crop habitat islands of various sizes (50 to 18,000 square metres) within one large field, as well as the arable land within the field, using pitfall traps in two consecutive sampling periods (spring to early summer and peak summer). The non-crop habitat islands situated inside arable land hosted many unique ground-dwelling arthropod species that were not present within the surrounding arable land. Even the smallest non-crop habitat islands with areas of tens of square metres were inhabited by assemblages substantially different from these inhabiting arable land and thus enhanced the biodiversity of agricultural landscapes. The non-crop habitat area substantially affected the activity density, recorded species richness and recorded species composition of carabid and ground-dwelling spider assemblages; however, the effects were weakened when species specialised to non-crop habitats species were analysed separately. Interestingly, recorded species richness of spiders increased with non-crop habitat area, whereas recorded species richness of carabid beetles exhibited an opposite trend. There was substantial temporal variation in the spatial distribution of ground-dwelling arthropods, and contrasting patterns were observed for particular taxa (carabid beetles and spiders). In general, local environmental conditions (i.e., non-crop habitat island tree cover, shrub cover, grass cover and litter depth) were better determinants of arthropod assemblages than non-crop habitat island size, indicating that the creation of quite small but diversified (e.g., differing in vegetation cover) non-crop habitat islands could be the most efficient tool for the maintenance and enhancement of diversity of ground-dwelling carabids and spiders in agricultural landscapes.     

The importance of small-scale heterogeneity in boreal forests: variation in diversity in forest-floor invertebrates across the succession gradient

Heterogeneity in species assemblages of forest-floor arthropods — carabid beetles, ants and spiders — within and between different forest age classes was studied in the southern Finnish taiga. The importance of processes operating on the local scale (within the movement radius of the species) vs on the regional scale (among forest stands) in determining the observed variation was assessed. Four data sets with different spatial resolutions in mesic forests in the same general study area were used. The material consists of 18 283 carabids of 51 species, 48 769 spiders of 212 species, and 126 718 worker ants of 23 species. Analyses of abundance variation and species complementarity among successional stages revealed that in all the three taxa species occurring in the mature forest were prevalent in the younger successional stages as well, constituting more than half of the catch in any age class. A great majority of carabid and spider species were widely distributed across the forest age classes, whereas ants include a higher proportion of species with a narrower amplitude across the succession gradient. Comparisons of similarity between samples at increasing distance from one another on the local scale within forest stands (a few tens of meters to a few hundreds of meters) showed a quite consistent pattern in carabids and spiders: there was more variation between sampling sites in young successional forests than in the mature forest. Furthermore, only in the mature forest a slight, albeit statistically not significant, negative relationship between similarity of samples and distance between sampling sites was detected. In carabids and spiders, comparisons between samples located at a distance of 10–15 m from each other showed considerable heterogeneity, the mean percentage similarity being c. 0.6 (in ants c. 0.8). On the regional scale, systematic variation between young and mature forest stands is a major element increasing the total diversity (species turnover c. 50% in carabids and spiders; compositional similarity c. 0.3–0.4 in carabids, 0.2–0.3 in spiders), but variation within forest stands on a spatial scale of 10–15 meters is another important component in the total heterogeneity. The results suggest that regional abundance variation is a primary factor influencing the composition of local assemblages; a set of hypotheses elaborating this conclusion is formulated. The result implies that maintenance of habitat heterogeneity on a small scale (10–15 m) is needed to preserve biodiversity in managed forests.     

Belowground carabid beetle diversity in the western Palaearctic - effects of history and climate on range-restricted taxa (Coleoptera, Carabidae)

Broad-scale patterns of subterranean diversity are a fascinating but neglected part of biodiversity research. Carabid beetles adapted to belowground habitats form a particularly species-rich part of the subterranean fauna. We studied large-scale diversity patterns of these belowground carabids across the western Palaearctic and evaluated potential impacts of historical and contemporary environmental conditions on the distribution of these taxa, using available species richness and environmental data at country level. Regression modelling and variation partitioning showed a strong relationship between species richness and range in elevation. Potential effects of climatic variables, mainly those related to ambient energy input, were much weaker. We discuss the implications of this combination of effects, which suggests, concordant with the absence of subterranean carabids in northern and highest richness in southern Europe, a strong prevailing influence of historical processes on current richness distributions of these taxa. Previous studies did not provide clear indications for such an influence. In contrast to more mobile and widespread carabid beetles, dispersal limitation due to high adaptation of belowground carabids to subterranean habitats has probably hindered their re-colonization of former permafrost and glaciated regions. Hotspots of highest belowground diversity are located in regions with an assumed long-term stability of environmental conditions, correlating with patterns of other dispersal-limited taxa such as many endemic plants. Our study provides important new information in the discussion of potential determinants of the distinct geographic patterns of belowground diversity. Moreover, it contributes to a better understanding of range size related differences previously found in the distribution of diversity and environmental dependencies of widespread and range-restricted species within the highly diverse carabid beetles.     

Differentiation of spring carabid beetle assemblages between semi‐natural habitats and adjoining winter wheat

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Useful model organisms,indicators, or both? Ground beetles (Coleoptera,Carabidae) reflecting environmental conditions

Classic studies have successfully linked single-species abundances, life-history traits, assemblage structures and biomass of carabid beetles to past and present, human-caused environmental impacts and variation in ‘natural’ conditions. This evidence has led many to suggest carabids to function as ‘indicators’ − a term that bears multiple meanings. Here, a conservation-oriented definition for an indicator is used, carabid indicator potential from seven views is evaluated, and ways to proceed in indicator research are discussed. (1) Carabid species richness poorly indicates the richness and abundance of other taxa, which underlines the importance of using multiple taxa in environmental assessments. The ability of assemblage indices and specialist or functional-group abundances to reflect rare species and habitats should be examined in detail. (2) Experimental evidence suggests that carabids may potentially serve as keystone indicators. (3) Carabids are sensitive to human-altered abiotic conditions, such as pesticide use in agro-ecosystems and heavy metal contamination of soils. Carabids might thus reflect ecological sustainability and ‘ecosystem health’. (4) Carabid assemblages host abundant species characteristic of particular habitat types or successional stages, which makes them promising dominance indicators. (5) Carabids reflect variation in ‘natural’ conditions, but vegetation and structural features are more commonly adopted as condition indicators. Carabids nevertheless provide yet another, equally accurate, view on the structure of the environment. (6) Carabids may function as early-warning signalers, as suggested by recent studies linking climate and carabid distributions. (7) Carabids reflect natural and human-caused disturbances and management, but the usefulness of these responses for conservation purposes requires further research. In summary, European carabids appear useful model organisms and possibly indicators because they are diverse, taxonomically and ecologically well-known, efficiently reflect biotic and abiotic conditions, are relevant at multiple spatial scales, and are easy to collect in sufficiently large numbers to allow statistical analyses. The assumption that carabid responses would reflect rare environmental conditions or the responses of rare and threatened species ‒ crucial information for conservationists and managers ‒ has not yet been critically evaluated. Even if it holds, the usefulness will be context dependent: species and their populations vary, conditions vary, questions put forward vary, and assessment goals vary.     

Ground beetle (Coleoptera: Carabidae) assemblages in conventional and diversified crop rotation systems

Ground beetles (Coleoptera: Carabidae) are important in agro-ecosystems as generalist predators of invertebrate pests and weed seeds and as prey for larger animals. However, it is not well understood how cropping systems affect ground beetles. Over a 2-yr period, carabids were monitored two times per month using pitfall traps in a conventional chemical input, 2-yr, corn/soybean rotation system and a low input, 4-yr, corn/soybean/triticale-alfalfa/alfalfa rotation system. Carabid assemblages were largely dominated by a few species across all cropping treatments with Poecilus chalcites Say comprising >70% of pitfall catches in both years of study. Overall carabid activity density and species richness were higher in the low input, 4-yr rotation compared with the conventionally managed, 2-yr rotation. There were greater differences in the temporal activity density and species richness of carabids among crops than within corn and soybean treatments managed with different agrichemical inputs and soil disturbance regimes. Detrended correspondence analysis showed strong yearly variation in carabid assemblages in all cropping treatments. The increase in carabid activity density and species richness observed in the 4-yr crop rotation highlights the potential benefits of diverse crop habitats for carabids and the possibility for managing natural enemies by manipulating crop rotations.     

Effects of urbanization on ground beetle assemblages (Coleoptera, Carabidae) of grassland habitats in western Canada

We pitfall-trapped carabid beetles across an urban-rural gradient in central Alberta, Canada to assess the relative contributions of landscape structure and habitat quality in explaining variation in composition of assemblages. The gradient ranged from the "urban" zone in the city of Edmonton, through a "suburban" zone just outside the city, into a "rural" zone 25–60 km east of the city. We trapped beetles at three replicated sites for each of two habitats (unmanaged grasslands and highly managed graveyards) in each of the three zones. Most of the 24 species (3162 individuals) captured were commonly associated with open habitats. Pterostichus melanarius , an introduced species, made up 80% of the total catch. Carabid assemblages of grasslands and graveyards were distinct, with lower species richness and lower catch rates of native, introduced and brachypterous carabids in graveyards. Graveyard assemblages also had proportionally fewer brachypterous carabid individuals (32 vs 52%) and species (20 vs 36%), suggesting that populations recruit locally from elsewhere after disturbances. Native carabids were least abundant in the urban areas. Brachypterous carabids were similarly abundant across the gradient, but more occurred in the urban zone than elsewhere (32 vs 5–10%). Samples from graveyards were characterized by lower beta diversity (variation among samples) than those from grasslands, but beta diversity was more-or-less equally variable across the gradient within habitats. The amount of unmanaged grassland habitat and the degree of urbanization significantly influence carabid assemblages, and therefore are relevant to management and conservation of urban grassland areas.     

Impact of the invasive moss Campylopus introflexus on carabid beetles (Coleoptera: Carabidae) and spiders (Araneae) in acidic coastal dunes at the southern Baltic Sea

Campylopus introflexus is an invasive moss in Europe and North America that is adapted to acidic and nutrient-poor sandy soils with sparse vegetation. In habitats like acidic coastal dunes (grey dunes) it can reach high densities, build dense carpets and modify habitat conditions. While the impact of the moss invasion on the vegetation is well analyzed, there is a lack of knowledge regarding possible effects on arthropods. In the present study we analyzed the impact of Campylopus introflexus on the ground-dwelling arthropods carabid beetles and spiders, as both taxa are known to be useful indicator taxa even on a small-scale level. In 2009 we compared species composition in a) invaded, moss-rich (C. introflexus) and b) native, lichen-rich (Cladonia spp.) acidic coastal dunes by using pitfall traps. A total of 1,846 carabid beetles (39 species) and 2,682 spiders (66 species) were caught. Species richness of both taxa and activity densities of spiders were lower in invaded sites. Species assemblages of carabids and spiders differed clearly between the two habitat types and single species were displaced by the moss encroachment. Phytophagous carabid beetles, web-building spiders and wolf spiders were more abundant in native, lichen-rich sites. Shifts in species composition can be explained by differences in the vegetation structure, microclimate conditions and most likely a reduced food supply in invaded sites. By forming dense carpets and covering large areas, the moss invasion strongly alters typical arthropod assemblages of endangered and protected (EU-directive) acidic coastal dunes.     

Organic versus conventional management in an apple orchard: effects of fertilization and tree-row management on ground-dwelling predaceous arthropods

1 Organic and conventional management of apple orchards may have a different effect on arthropod communities.
2 We conducted a 3-year study to assess the effect of two strategies of fertilizer treatment (organic versus chemical) and three tree-row management systems (straw mulching, tillage and herbicide) on activity-density and biodiversity of epigeic predators. Ground beetles (Carabidae), rove beetles (Staphylinidae), ants (Formicidae) and spiders (Araneae) were sampled monthly with pitfall traps in the same apple orchard during 2003, 2004 and 2005.
3 A total of 4978 individuals were collected. Carabids (56.8% of the total catches) were the most abundant taxonomic group, followed by spiders (20.7%), ants (14.8%) and rove beetles (7.7%). Tree-row management had a greater influence on predator catches than fertilizer treatment. Total predator catches were lower under the mulch. Mulching also reduced carabid abundance, but increased staphylinid catches.
4 Tree row management also had a significant effect on biodiversity parameters. Species richness did not significantly differ among treatments for ants, spiders or the total catches, but was higher on herbicide-treated plots for carabids and on mulched plots for staphylinids. Shannon–Wiener's diversity index was significantly greater in the mulched and herbicide treated plots for total predators and carabids. For staphylinids, this index was significantly greater on the mulched plots. Fertilizer application strategy only influenced the species richness of rove beetles, which was greater in the chemically-treated plots.
5 The results showed that a change from conventional to organic fertilizer treatment of apple trees may be performed without differential effects on predator activity-density or biodiversity. However, a change from herbicide treatment to mulching or mechanical weed control may be significant, depending on the taxonomic group.     

A field experiment on the effectiveness of spiders and carabid beetles as biocontrol agents in soybean

1 Spiders and carabid beetles are abundant generalist predators that prey upon insect pests of soybean. A field experiment was conducted to determine the impact of spiders and carabids on soybean yield. Prior to planting, three 7 × 7 m plots were fenced in order to reduce spider and carabid immigration. Carabids that emerged within the plots were not removed, but spiders that ballooned into these predator‐reduction plots or that entered by climbing the fence were removed by pitfall trapping and searching the vegetation. Three unmanipulated, unfenced plots served as the control treatment. 2 Densities of spiders on soybean vegetation, and activity‐densities of spiders and carabids determined by pitfall trapping, were c. 75% lower in the spider‐carabid reduction treatment than in control plots. Despite clear differences between treatments in numbers and activity of these major generalist predators, the weight of soybeans harvested did not differ between control and spider‐carabid reduction plots. 3 Paralleling the absence of an effect of predator reduction on soybean yield was the absence of any significant difference between treatments in densities of whiteflies (Aleyrodidae), leafhoppers (Cicadellidae), thrips (Thysanoptera), Lepidoptera larvae and herbivorous Coleoptera. 4 Our experiment provides no evidence that spiders and carabid beetles at ambient densities affect soybean yield. Low populations of pest species or low predation pressure on soybean pests by spiders and carabids at the ambient densities of this experiment could be responsible for this result.     

Understanding the impact of flooding on trait-displacements and shifts in assemblage structure of predatory arthropods on river banks

1. Species assemblages of naturally disturbed habitats are governed by the prevailing disturbance regime. Consequently, stochastic flood events affect river banks and the inhabiting biota. Predatory arthropods occupy predominantly river banks in relation to specific habitat conditions. Therefore, species sorting and stochastic processes as induced by flooding are supposed to play important roles in structuring riparian arthropod assemblages in relation to their habitat preference and dispersal ability. 2. To ascertain whether assemblages of spiders and carabid beetles from disturbed river banks are structured by stochastic or sorting mechanisms, diversity patterns and assemblage-wide trait-displacements were assessed based on pitfall sampling data. We tested if flooding disturbance within a lowland river reach affects diversity patterns and trait distribution in both groups. 3. Whereas the number of riparian spider species decreased considerably with increased flooding, carabid beetle diversity benefited from intermediate degrees of flooding. Moreover, regression analyses revealed trait-displacements, reflecting sorting mechanisms particularly for spiders. Increased flooding disturbance was associated with assemblage-wide increases of niche breadth, shading and hygrophilic preference and ballooning propensity for spider (sub)families. Trait patterns were comparable for Bembidiini carabids, but were less univocal for Pterostichini species. Body size decreased for lycosid spiders and Bembidiini carabids with increased flooding, but increased in linyphiid spiders and Pterostichini carabids. 4. Our results indicate that mainly riparian species are disfavoured by either too high or too low degrees of disturbance, whereas eurytopic species benefit from increased flooding. Anthropogenic alterations of flooding disturbance constrain the distribution of common hygrophilous species and/or species with high dispersal ability, inducing shifts towards less specialized arthropod assemblages. River banks with divergent degrees of flooding impact should be maintained throughout dynamic lowland river reaches in order to preserve typical riparian arthropod assemblages.     

The impact of forest ski-pistes on diversity of ground-dwelling arthropods and small mammals in the Alps

Forest clearing for winter sport activities is the major force driving loss and fragmentation of the alpine forests. The establishment of ski-pistes involves impacts on every ecosystem component. To assess the extent of this threat we studied ground-dwelling arthropods (namely ground beetles and spiders) and small mammals (shrews and voles) at two ski resorts in north-western Italian Alps by pitfall trapping. Diversity parameters (mean abundance, species richness and Shannon index) of spiders and macropterous carabids increased from forest interior to open habitats (i.e., ski-piste or pasture), whereas parameters of brachypterous carabids significantly decreased from forest interior to open habitats. Diversity parameters of macropterous ground beetles were higher on pastures than on ski-pistes. Small mammals were virtually absent from ski-pistes. Observed frequencies in the three adjacent habitats were significantly different from expected ones for the bank vole Myodes glareolus and the pygmy shrew Sorex minutus. Generalized linear models showed that abundance, species richness and diversity of spiders and macropterous carabids of ski-pistes were best modelled by combination of factors, including grass cover and width of the ski-piste. Indicator Species Analysis showed that species that significantly preferred ski-pistes were less than those preferring pastures, and species which were exclusive of ski-pistes were very few. To retain arthropod ground-dwelling fauna of open habitats environmentally friendly ways of constructing pistes should be developed. After tree clearing, only the roughest ground surfaces should be levelled, in order to preserve as much natural vegetation as possible. Where necessary, ski-pistes should be restored through the recovery of local vegetation.     

The impact of hedge-forest connectivity and microhabitat conditions on spider and carabid beetle assemblages in agricultural landscapes

Agricultural intensification in terms of decreasing landscape complexity and connectivity has negatively affected biodiversity. Linear landscape elements composed of woody vegetation like hedges may counteract this negative trend by providing habitats and enhancing habitat connectivity for different organisms. Here, we tested the impacts of habitat type (forest edges vs. hedges) and hedges’ isolation (connected vs. isolated hedges) from forests as well as microhabitat conditions (percentage of bare ground and width) on trait-specific occurrence of ground-dwelling arthropods, namely spiders and carabids. Arthropods were grouped by habitat specialisation (forest vs. open-habitat species vs. generalists), hunting strategy (web-building or hunting spiders) and dispersal ability (wing morphology of carabids). Spider and carabid assemblage composition was strongly influenced by habitat type and isolation, but not by microhabitat conditions. Activity density of forest species and brachypterous carabids was higher in forest edges compared to hedges, whereas open-habitat species and macropterous carabids showed reverse patterns, with no effects of isolation. Occurrence of generalist carabids, but not spiders, was higher in hedges compared to forest edges. Habitat type and isolation did not affect spiders with different hunting strategy. Microhabitat conditions were less important for spider and carabid occurrence. Our study concludes that on a landscape scale, type of linear woody habitat is more important for arthropod occurrence than isolation effects and microhabitat conditions, depending on traits. Hedges provide refuges for species specialised to open habitats and species with high dispersal ability, such as macropterous carabids. Forest edges enhance persistence of species specialised to forests and species with low dispersal ability, such as brachypterous carabids.     

Functional diversity and habitat preferences of native grassland plants and ground‐dwelling invertebrates in private gardens along an urbanization gradient

Urbanization is occurring around the globe, changing environmental conditions and influencing biodiversity and ecosystem functions. Urban domestic gardens represent a small‐grained mosaic of diverse habitats for numerous species. The challenging conditions in urban gardens support species possessing certain traits, and exclude other species. Functional diversity is therefore often altered in urban gardens. By using a multi‐taxa approach focused on native grassland plants and ground‐dwelling invertebrates with overall low mobility (snails, slugs, spiders, millipedes, woodlice, ants, rove beetles), we examined the effects of urbanization (distance to city center, percentage of sealed area) and garden characteristics on functional dispersion, functional evenness, habitat preferences and body size. We conducted a field survey in 35 domestic gardens along a rural–urban gradient in Basel, Switzerland. The various groups showed different responses to urbanization. Functional dispersion of native grassland plants decreased with increasing distance to the city center, while functional dispersion of ants decreased with increasing percentage of sealed area. Functional evenness of ants increased with increasing distance to the city center and that of rove beetles decreased with increasing percentage of sealed area. Contrary to our expectation, in rove beetles, the proportion of generalists decreased with increasing percentage of sealed area in the surroundings, and the proportion of species preferring dry conditions increased with increasing distance to the city center. Body size of species increased with distance to city center for slugs, spiders, millipedes, ants, and rove beetles. Local garden characteristics had few effects on functional diversity and habitat preferences of the groups examined. Our study supports the importance of using multi‐taxa approaches when examining effects of environmental change on biodiversity. Considering only a single group may result in misleading findings for overall biodiversity. The ground‐dwelling invertebrates investigated may be affected in different ways from the more often‐studied flying pollinators or birds.     

Carabid beetles as indicators for shrub encroachment in dry grasslands

Semi-natural grasslands are key habitats for biodiversity conservation in Central Europe. Shrub encroachment is one of the most threatening drivers of grassland degradation and affects soil properties, microclimate, and vegetation with possible impacts on higher trophic levels. We aimed to analyse the impact of shrub encroachment with broom (Cytisus scoparius) on carabid beetle diversity, species composition, and functional traits. In a field study on dry grasslands on the island of Hiddensee (Germany) we studied 15 sites along a gradient of increasing broom encroachment and classified them into three dry grassland types with low, medium, and high shrub cover. Our results provide evidence that shrub encroachment initially has positive effects on species richness and activity densities of dry grassland carabids. Carabid species composition differed among differently shrub-covered dry grassland types, and sites with low and high shrub cover were each characterised by unique carabid assemblages. The species composition of sites with a medium shrub biomass had a transitional character and contained species which are typical for open dry grassland, but also shared species with sites with a high shrub cover. Among functional trait parameters investigated, especially the body size of carabid beetles was related to environmental parameters associated with shrub encroachment. Body size was positively correlated to shrub biomass and soil humidity, but negatively to temperature. Eurytopy values of carabids were related to high litter cover, i.e. habitat generalist (eurytopic) species mainly occurred in densely shrub-encroached sites. In order to preserve unique carabid assemblages of open dry grasslands with stenotopic and smaller species, it is most important to prevent a shrub encroachment higher than about 60% cover. For management we suggest extensive grazing (by cattle, sheep or horses) to prevent shrub encroachment on dry grasslands. In areas with high shrub cover additionally the use of goats or mechanical removal of shrubs might be necessary.     

Distribution of carabid beetles (Coleoptera: Carabidae) across a forest-grassland ecotone in southwestern China

This paper studied the occurrence of carabid beetles (Coleoptera: Carabidae) in the forest edge, the adjacent forest interior, and the surrounding grassland in southwestern China. Beetles were collected with pitfall traps along five replicated transects. Forest species rarely penetrated into the grassland from the forest interior, and the grassland specialists were not found in the forest interior. The forest edge hosted additional species from the adjacent grassland that increased its overall species richness. Nearly all forest species (23 of 24 species) and grassland species (13 of 15 species) can be found in the forest edge. Carabids of the forest edge were more similar to those of the forest interior than to those of the grassland by ordination and cluster analysis. Based on the specificity and fidelity, carabids can be distinguished into five species groups: habitat generalists, grassland-associated species, forest generalists, forest specialists, and edge-associated species. Multiple linear regression analysis showed that canopy cover and/or shrub cover were the most important factors in determining the richness, abundance, and diversity of carabids. The forest edge may serve as a transition zone for dispersal and re-colonization of carabid beetles from adjacent habitats and therefore is important for natural conservation.     

Response of carabid beetles (Coleoptera: Carabidae) and spiders (Araneae) to coastal heathland succession

We analyzed the impacts of succession and grass encroachment on carabid beetle and spider assemblages in a coastal heathland. Further, indicator species for different successional stages (grey dunes, dwarf-shrub heath, grassy heath, heath with shrubs, birch forest) were identified, and their relations to habitat parameters were analyzed. The study was conducted on the Baltic island of Hiddensee, Germany. Ground-dwelling arthropods were sampled using pitfall traps along a successional gradient containing five stages. Ordination by nonmetric multidimensional scaling (NMDS) and analysis of similarities (ANOSIM) revealed a clear separation of species composition among the successional stages. Both in carabid beetles and spiders, most indicator species were obtained in the youngest stage (grey dunes) and fewest in the intermediate stages (grassy heath, heath with shrubs). Also the proportion of endangered species was highest in grey dunes. Based on our results, conservation management of coastal heathlands should preserve a mosaic of different successional stages with a clear preference on younger stages (grey dunes and dwarf-shrub heath).     

Progressively excluding mammals of different body size affects community and trait structure of ground beetles

Mammalian grazing induces changes in vegetation properties in grasslands, which can affect a wide variety of other animals including many arthropods. However, the impacts may depend on the type and body size of these mammals. Furthermore, how mammals influence functional trait syndromes of arthropod communities is not well known. We progressively excluded large (e.g. red deer, chamois), medium (e.g. alpine marmot, mountain hare), and small (e.g. mice) mammals using size‐selective fences in two vegetation types (short‐ and tall‐grass vegetation) of subalpine grasslands. We then assessed how these exclusions affected the community composition and functional traits of ground beetles (Coleoptera, Carabidae), and which vegetation characteristic mediated the observed effects. Total carabid biomass, the activity densities of carabids with specific traits (i.e. small eyes, short wings), the richness of small‐eyed species and the richness of herbivorous species were significantly higher when certain mammals were excluded compared to when all mammals had access, regardless of vegetation type. Excluding large and medium mammals increased the activity density of herbivorous carabid species, but only in short‐grass vegetation. Similarly, excluding large mammals (ungulates) altered carabid species composition in the short‐, but not in the tall‐grass vegetation. All these responses were related to aboveground plant biomass, but not to plant Shannon diversity or vegetation structural heterogeneity. Our results indicate that changes in aboveground plant biomass are key drivers of mammalian grazers’ influence on carabids, suggesting that bottom–up forces are important in subalpine grassland systems. The exclusion of ungulates provoked the strongest carabid response. Our results, however, also highlight the ecological significance of smaller herbivorous mammals. Our study furthermore shows that mammalian grazing not only altered carabid community composition, but also caused community‐wide functional trait shifts, which could potentially have a wider impact on species interactions and ecosystem functioning.