Ground-dwelling Arthropods Research Articles

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.

A Preliminary Assessment of the Ground-Dwelling Arthropod Community Composition in Six Common Dune Cover Types at Cape Cod National Seashore

We provide a preliminary assessment of the ground-dwelling arthropod com- munity composition in six common coastal dune ecosystem land cover-types at Cape Cod National Seashore. We captured 6815 individual arthropods representing 16 arthropod orders from 1008 terrestrial pitfall trap-nights. The most abundant orders were Hyme- noptera, Diptera, Araneae, and Isopoda (76.1%, 8.5%, 5.5%, and 3.3% of total captures, respectively). There were differences in ground-dwelling arthropod community compo- sition among the three early-successional and the three later-successional cover types, with the latter having a greater overall arthropod diversity and higher capture rates for a number of the major arthropod taxa captured. Our report is among the first community- wide analyses of arthropod community composition in coastal dune ecosystems of the northeastern US. The results from this study should be viewed as a preliminary assess- ment given that: 1) we employed a single trapping method (i.e., pitfall traps); 2) traps were only open during the late-afternoon to early morning hours, and only during the summer months; and 3) captured arthropods were classified only to order. We hope our report will inspire additional research of coastal dune arthropod communities.

Differential responses of ground dwelling arthropods to ski-piste restoration by hydroseeding

The construction of ski-pistes can cause serious damage to all the components of an ecosystem and may therefore be considered as one of the main causes of human-driven environmental changes in mountain habitats. This study was aimed at assessing the responses of different ground dwelling arthropod assemblages (i.e. ground beetles, spiders and grasshoppers) to ski-piste restoration through hydroseeding with commercial seed mixtures. The soil, vegetation and arthropods of restored and un-restored ski-pistes and the adjacent grassland have been sampled at two high altitude sites in the north-western Italian Alps. The ski-piste soil was characterized by a higher skeletal content and, consequently, a lower amount of fine earth and organic matter than that of the undisturbed adjacent grassland. The plant cover of the restored ski-pistes was very low above 2,500 m a.s.l.; the vegetation cover below this threshold was higher in the study area, mainly due to the seeded species. The unrestored ski-pistes showed very large proportions of bare ground. The responses of the three ground-dwelling arthropod groups to vegetation conditions were different. GLMMs and IndVal analyses showed that all three groups avoided the unrestored ski-pistes plots, which were characterized by a very scarce vegetation cover, irrespective of the altitude. The low altitude plots of the restored ski-pistes, which were characterized by a high vegetation cover, had a significantly larger number of grasshoppers on the ski-pistes than on the adjacent grassland plots. Moreover, these restored ski-piste plots were used in equal proportion to the adjacent grassland plots by ground beetles but avoided by spiders. When ski-pistes become sufficiently revegetated by hydroseeded plants, they are colonized by grasshoppers and, to a lesser extent, by ground-beetles. Spiders, instead, do not colonize the pistes, thus demonstrating that they are the most sensitive arthropods and may therefore represent the best indicators of human-driven environmental changes in high altitude alpine habitats.

The habitat-specific effects of highway proximity on ground-dwelling arthropods: Implications for biodiversity conservation

The total length of highways worldwide has increased continuously over recent decades. Highways and their roadside verges may substantially affect species dispersal, and the ecological effects of highways often extend to neighbouring areas. This study investigated the effects of highways on assemblages of ground-dwelling arthropods in neighbouring forest and open habitats. In total, 24 sites within five highway segments situated in the Czech Republic were sampled using transects of pitfall traps placed at increasing distances (0, 50 and 100m) from the edge of highway verges. The total catch size and species richness of ground-dwelling spiders and beetles varied more strongly with distance from the highway edge in forest habitats than in open habitats. Species composition of both spiders and beetles was significantly affected by distance from the highway edge in open habitats as well as in forest habitats. In general, the species richness of forest specialist beetles (but not of spiders) was negatively affected by highway proximity in forested sites, whereas habitat generalists and open habitat specialists (both spiders and beetles) benefited from proximity to a highway in both forest and open habitats. Our results indicate that highway verges may potentially enhance local assemblages of ground dwelling spiders and beetles because they provide suitable sites (in intensively managed open landscapes) or dispersal corridors (in forested landscapes) for habitat generalists and open habitat specialist species. However, negative effects on forest specialists must also be considered, especially in landscapes with little forest. The landscape context should be given substantial consideration in future decisions about highway location because possible threats to forest specialists and benefits for other species must be recognised and balanced.

Assessment of the potential impact of a Bt maize hybrid expressing Cry3Bb1 on ground beetles (Carabidae)

The potential impact of a Bt maize hybrid expressing the coleopteran specific Cry3Bb1 on non-target organisms was assessed in a field release experiment. The study examined the relative abundance of ground beetles (Carabidae) in four maize varieties including the genetically engineered DKC 5143-Bt (event MON 88017), its near-isogenic line DKC 5143 and the two conventional varieties DK 315 and Benicia. Pitfall traps were used to collect the ground dwelling arthropods, which were analyzed to species level. Statistical comparisons showed no significant differences of ground beetle activity densities and diversity patterns between the Bt maize and the near isoline. The internal contents of the Bt protein Cry3Bb1 in ground beetles collected from the field were measured with ELISA. The Bt protein was found in 47% of the ground beetles sampled in Bt plots before the anthesis and in 66% of the individuals sampled after the beginning of maize anthesis.

Roadside habitats: effects on diversity and composition of plant, arthropod, and small mammal communities

Road edge effects cover extensive areas and exert a wide range of ecological influences on nearby plants and animals. Most studies have focused on individual and population level effects of the road edge; less is known about how communities and their functionality are altered in proximity to roads. Here, we studied the effect of road edges on species richness, rarity, endemism, composition, and functional (trophic) classification of communities of plants, ground-dwelling arthropods (beetles, spiders, scorpions, diplopods), and small mammals. The study, conducted in a Mediterranean ecosystem in central Israel, included sampling of these taxa in 10 plots adjacent to a regional road, and in 12 nearby control plots located in a typical shrubland habitat. We found a variety of community level road edge effects on the structure, composition, and function of the studied communities. The extent of effects varied among taxa, but they were generally positive or neutral. For the species-rich taxa (plants, beetles, and spiders), distinct road edge communities characterized by higher richness and altered species composition were found. Rarity and endemism were lower, and the proportion of disturbance-associated plant species was higher at the road edge. Among the species-poor taxa, scorpions and small mammals were more abundant along road edges than in control plots, while diplopods, the only negatively affected taxon, showed decreased abundance along the road. No ecologically meaningful changes in richness or composition were detected for the species-poor taxa along the road edge. Road edges profoundly affect floral and faunal communities, with possible implications for biodiversity conservation.

Loss of a foundation forest species due to an exotic invader impacts terrestrial arthropod communities

The hemlock woolly adelgid (Adelges tsugae) is an invasive insect native to Asia that feeds on all species of hemlock (Tsuga spp.), and is rapidly spreading throughout the range of eastern hemlock (T. canadensis). Eastern hemlock is an essential component of forested communities, is particularly susceptible to the adelgid, and has already suffered extensive mortality throughout much of its range. Hemlock dominated forests in the central Appalachians are expected to shift to deciduous species following adelgid-induced hemlock mortality, leading to shifts in epigeic macroinvertebrates. In a 2-year study using pitfall traps, we compared abundance, diversity, and composition of ground dwelling arthropod taxa and feeding guilds associated with riparian zones dominated by eastern hemlock to those associated with deciduous trees in the southern Appalachians. Differences were detected for the Diplopoda (millipedes) and Isopoda (pillbugs and wood lice), and for Formicidae (ants) and Staphylinidae (rove beetles). Each was more abundant beneath deciduous canopies than eastern hemlock canopies. Our comparative evaluation of eastern hemlock and deciduous riparian zone arthropod communities depicts the potential end point of a likely successional trajectory of eastern North American forests invaded by hemlock woolly adelgid. Our results indicate probable shifts in arthropod communities as the hemlock woolly adelgid invasion progresses through the Central Appalachian region.

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.

Habitat structure and food resources for wildlife across successional stages in a tropical forest

Tropical forests are experiencing an increase in the proportion of secondary forests as a result of the balance between the widespread harvesting of old-growth forests and the regeneration in abandoned areas. The impacts of such a process on biodiversity are poorly known and intensely debated. Recent reviews and multi-taxa studies indicate that species replacement in wildlife assemblages is a consistent pattern, sometimes stronger than changes in diversity, with a replacement from habitat generalists to old-growth specialists being commonly observed during tropical forest regeneration. However, the ecological drivers of such compositional changes are rarely investigated, despite its importance in assessing the conservation value of secondary forests, and to support and guide management techniques for restoration. By sampling 28 sites in a continuous Atlantic forest area in Southeastern Brazil, we assessed how important aspects of habitat structure and food resources for wildlife change across successional stages, and point out hypotheses on the implications of these changes for wildlife recovery. Old-growth areas presented a more complex structure at ground level (deeper leaf litter, and higher woody debris volume) and higher fruit availability from an understorey palm, whereas vegetation connectivity, ground-dwelling arthropod biomass, and total fruit availability were higher in earlier successional stages. From these results we hypothetize that generalist species adapted to fast population growth in resource-rich environments should proliferate and dominate earlier successional stages, while species with higher competitive ability in resource-limited environments, or those that depend on resources such as palm fruits, on higher complexity at the ground level, or on open space for flying, should dominate older-growth forests. Since the identification of the drivers of wildlife recovery is crucial for restoration strategies, it is important that future work test and further develop the proposed hypotheses. We also found structural and functional differences between old-growth forests and secondary forests with more than 80years of regeneration, suggesting that restoration strategies may be crucial to recover structural and functional aspects expected to be important for wildlife in much altered ecosystems, such as the Brazilian Atlantic forest.

Food Availability, Foraging Behavior, and Diet of Autumn Migrant Landbirds in the Boise Foothills of Southwestern Idaho

Abstract. Food availability and acquisition are critical components of a stopover site's suitability, but we know relatively little about how changes in food availability affect the stopover ecology of migrating landbirds. We examined fruit and arthropod availability in three habitats, studied foraging behavior and diet, and investigated use versus availability for passerines migrating through southwestern Idaho in autumn. Hemiptera dominated foliage-dwelling arthropod communities in all three habitats, whereas Hymenoptera were most numerous among ground-dwelling arthropods. Mountain shrubland had relatively high biomass of both ground-dwelling and foliage-dwelling arthropods, whereas conifer forest had high biomass of foliage-dwelling arthropods only and shrubsteppe had high biomass of ground-dwelling arthropods only. Species' foraging behavior varied, but most species foraged in mountain shrubland more often than expected by chance. Diets of most species included a high proportion of certain Hemiptera a...

Shrubs and species identity effects on the distribution and diversity of ground-dwelling arthropods in a Gobi desert

Disentangling the relationship between shrub vegetation and ground-dwelling arthropods at multiple levels of taxonomic resolution is essential to developing a suitable management strategy for the conservation of shrub-associated arthropod biodiversity in shrubland ecosystems. Using Gobi desert (dominated by shrub species Nitraria sphaerocarpa and Reaumuria soongorica) occurring widely in inland arid areas of northwest China as a model system, we sampled ground-dwelling arthropods by pitfall trapping method under canopies of both shrubs and in intershrub bare areas during spring, summer and autumn. Our aim was to determine whether the presence and species identity of shrubs influence the distribution of ground-dwelling arthropods and whether the influence of shrub presence and species identity differs among trophic and taxonomic groups. At the community level, total arthropod abundance and species richness were significantly greater under shrubs than in intershrub bare habitats, whereas more arthropods were captured under N. sphaerocarpa than under R. soongorica. At the trophic group level, the abundance of predator and decomposer arthropods was significantly greater under shrubs than in intershrub bare habitats, whereas herbivore and decomposer arthropods were more abundant under N. sphaerocarpa than under R. soongorica. At the family level, the abundance of Carabidae, Gnaphosidae, Karschiidae, Tenebrionidae and Thomisidae was consistently much greater under shrubs than in intershrub bare habitats, whereas that of Formicidae, Philodromidae and Tettigoniidae did not differ between the shrub microhabitats and the intershrub bare habitats. However, the abundance of Curculionidae under R. soongorica and the abundance of Geotrupidae under N. sphaerocarpa were significantly lower than that in intershrub bare habitats. N. sphaerocarpa was commonly preferred by arthropods in the families of Curculionidae and Tenebrionidae, whereas R. soongorica was commonly preferred by arthropods in the family Geotrupidae, but shrub species identity did not affect the abundance of the remaining families. Our results suggest that shrubs and species identity play important roles in structuring ground-dwelling arthropod communities, but the response of arthropods differed among trophic or taxonomic groups. This study may have important implications for the conservation of invertebrate biodiversity in Gobi desert ecosystems.

Stand type is more important than red wood ant abundance for the structure of ground-dwelling arthropod assemblages in managed boreal forests

1 The relationships between red wood ants (Formica rufa group) and other ground-dwelling arthropods were studied in young managed forests stands in Eastern Finland. The main objectives were: (i) to test the influence of stand type (dominant tree species; age: sapling versus pole stage) and numbers of red wood ants on the occurrence of other ground-dwelling arthropods and (ii) to study the occurrence of red wood ants versus other arthropods on a distance gradient from ant mounds. We used pitfall traps set in 5–14-year-old sapling stands and 30–45-year-old pole-stage stands of Scots pine (Pinus sylvestris L.) and birch (Betula spp.) forests. 2 Pitfall trap catches of red wood ants did not vary significantly between the forest stand types, although some groups of other arthropods showed clear responses to stand type (e.g. catches of other Formicinae and Gnaphosidae were higher in sapling stands than in pole-stage stands). The number of red wood ants clearly explained less of the variation in assemblages of other ground-dwelling arthropods than the forest stand type. 3 Red wood ant numbers decreased significantly with distance from the mounds, but the other ground-dwelling arthropods were insensitive to this gradient or even showed a preference for proximity to ant mounds and high ant activity. 4 The results obtained in the present study suggest that wood ants do not have strong effects on several other ground-dwelling arthropod groups in young managed forests other than in the immediate vicinity of their mounds.

Facilitative Ecological Interactions Between Invasive Species: Arundo donax Stands as Favorable Habitat for Cattle Ticks (Acari: Ixodidae) Along the U.S.-Mexico Border

The cattle tick, Rhipicephalus (Boophilus) spp. is a key vector of protozoa that cause bovine babesiosis. Largely eradicated from most of the United States, the cattle tick continues to infest south Texas, and recent outbreaks in this area may signal a resurgence of cattle tick populations despite current management efforts. An improved understanding of the dynamic ecology of cattle fever ticks along the U.S.-Mexico border is required to devise strategies for sustainable eradication efforts. Management areas of the cattle tick overlap considerably with dense, wide infestations of the non-native, invasive grass known as giant reed (Arundo donax L.). Here we show that stands of giant reed are associated with abiotic and biotic conditions that are favorable to tick survival, especially when compared with other nearby habitats (open pastures of buffelgrass (Pennisetum ciliare) and closed canopy native forests). Overhead canopies in giant reed stands and native riparian forests reduce daily high temperature, which was the best abiotic predictor of oviposition by engorged females. In sites where temperatures were extreme, specifically open grasslands, fewer females laid eggs and the resulting egg masses were smaller. Pitfall trap collections of ground dwelling arthropods suggest a low potential for natural suppression of tick populations in giant reed stands. The finding that A. donax infestations present environmental conditions that facilitate the survival and persistence of cattle ticks, as well or better than native riparian habitats and open grasslands, represents an alarming complication for cattle fever tick management in the United States.

Arthropod Communities Associated with Habitats Occupied by Breeding Swainson's Warblers

Abstract. The Swainson's Warbler (Limnothlypis swainsonii) is an insectivorous songbird and a species of conservation concern in the southeastern U.S. Because it is specialized for foraging in the litter of the forest floor, it is dependent on a well-developed leaf-litter layer. However, this reliance on the litter layer likely reflects selection of habitats with abundant arthropods for food. To investigate this possibility, we examined relationships between Swainson's Warbler presence and both abundance and diversity of ground-dwelling and litter arthropods. In 2004 and 2005, using song playbacks, we surveyed 1453 sites and collected arthropods in litter samples and pitfall traps at 45 randomly selected occupied and unoccupied sites. In litter samples, total mean arthropod abundance, abundance of arthropods ≥5 mm in length, total abundance of adults, and taxonomic richness were significantly greater at sites occupied by Swainson's Warblers than at unoccupied sites. In pitfall data, however, we detected n...

Large-scale experimental landscapes reveal distinctive effects of patch shape and connectivity on arthropod communities

The size, shape, and isolation of habitat patches can affect organism behavior and population dynamics, but little is known about the relative role of shape and connectivity in affecting ecological communities at large spatial scales. Using six sampling sessions from July 2001 until August 2002, we collected 33,685 arthropods throughout seven 12-ha experimental landscapes consisting of clear-cut patches surrounded by a matrix of mature pine forest. Patches were explicitly designed to manipulate connectivity (via habitat corridors) independently of area and edge effects. We found that patch shape, rather than connectivity, affected ground-dwelling arthropod richness and beta diversity (i.e. turnover of genera among patches). Arthropod communities contained fewer genera and exhibited less turnover in high-edge connected and high-edge unconnected patches relative to low-edge unconnected patches of similar area. Connectivity, rather than patch shape, affected the evenness of ground-dwelling arthropod communities; regardless of patch shape, high-edge connected patches had lower evenness than low- or high-edge unconnected patches. Among the most abundant arthropod orders, increased richness in low-edge unconnected patches was largely due to increased richness of Coleoptera, whereas Hymenoptera played an important role in the lower evenness in connected patches and patterns of turnover. These findings suggest that anthropogenic habitat alteration can have distinct effects on ground-dwelling arthropod communities that arise due to changes in shape and connectivity. Moreover, this work suggests that corridors, which are common conservation tools that change both patch shape and connectivity, can have multiple effects on arthropod communities via different mechanisms, and each effect may alter components of community structure.

Ground-Dwelling Arthropod Distribution and Movement Across a Fragmented Riparian Forest

Abstract The ability to predict patterns of species dispersal across habitat edges takes on increasing conservation relevance as land-scapes become more fragmented. We assessed edge responses for four ground-dwelling arthropod taxa by measuring their distribution and movement patterns across a forest edge associated with a forested riparian buffer and an adjacent upslope clearcut at a single site. We used Spatial Analysis by Distance Indices to describe the spatial distribution of arthropods, habitat variables, and the associations between them across a 49 × 63 m pitfall trapping grid with 80 trapping stations. We used mark-release-recapture techniques to measure the distance, rate, and direction of arthropod movement within and between habitat types. Scaphinotus angusticollis (Coleoptera; Carabidae) was restricted to the cool, moist portion of the riparian buffer and was not observed to cross the forest edge. The carabids Pterostichus lattini and Scaphinotus marginatus had more eurytopic distributions ac...

Does the decline of red wood ants after clear-cutting favour epigeic arthropods?

In forest ecosystems in the temperate and boreal zones in Europe, red wood ants (RWA, Formica rufa group) have a significant affect as predators and competitors in communities of ground-dwelling arthropods. Therefore, the spatiotemporal distribution and abundance of RWA affect the distribution of many other species. The hypothesis that a reduction in the abundance of RWA in clear-cut areas enables other arthropods to increase in abundance was tested. The study was conducted in NW Poland in 2007 and 2008. A total of 276 1×1 m plots were sampled and 1,696 individuals recorded. The probability of the occurrence of RWA decreased significantly towards the center of clear-cut areas and increased with increasing plant cover. The frequency of Lasius platythorax, Formica fusca and spiders in the plots significantly increased towards the edge of a clear-cut area. Moreover, the occurrence of L. platythorax was negatively associated with the presence of RWA, while that of the Myrmica species was positively associated. The effect of the distance to the edge of a clear-cut area seems to be much more pronounced than the effect of RWA. This suggests that the arthropods studied prefer habitats close to the edge that are utilized by RWA than RWA-free sites located in the centre of clear-cut areas.

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).

Weed management practices determine plant and arthropod diversity and seed predation in vineyards

Sanguankeo PP & León RG (2011). Weed management practices determine plant and arthropod diversity and seed predation in vineyards. Weed Research51, 404–412.SummaryIn the Central Coast of California, USA, wine grape growers are making efforts to identify weed control practices that preserve biodiversity in their vineyards while maintaining yields. A field study was conducted in Paso Robles, California in 2006 and 2007 evaluating the effect on plant and ground dwelling arthropod communities of five weed control practices conducted under the vines within the row (berm): (i) flumioxazin, (ii) simazine, (iii) cultivation, (iv) cover crop and (v) untreated control. The cover crop, cultivation and untreated control had 4–50 times higher plant density and more than 15 times higher plant diversity compared with the herbicide treatments. The arthropod activity‐density differed among treatments only in 2007, being higher in the cover crop and untreated control. There was a positive relationship between plant and arthropod diversity (r2 = 0.42, P = 0.02 in 2006; r2 = 0.64, P < 0.001 in 2007). Laboratory seed predation tests of the two most frequently captured carabid beetles, Calathus ruficollis and Tanystoma maculicolle, indicated they predated more of the common weed species Brassica nigra and Capsella bursa‐pastoris, than other weed species tested. Under field conditions, treatments with higher plant diversity and density favoured arthropod seed predation of these weeds. Predation rates were 20–40% in the cover crop and untreated control, double that observed in the herbicide treatments. The cultivation treatment balanced the benefits of promoting diversity while minimising yield reductions caused by weed competition. The results indicate that weed management practices that promote higher plant diversity and density have the potential to yield ecological benefits within vineyards, for example, enhancing the activity of beneficial organisms.

Ground-dwelling arthropod assemblages of partially improved heathlands according to the species of grazer and grazing regime

The creation of improved areas is one way of increasing the productivity of livestock on Cantabrian heathland (NW Spain), a habitat that is frequently located in less favourable mountainous areas where the development of sustainable husbandry is limited. The effect of this on the biodiversity of heathland is unclear and likely to depend on several factors, such as the grazing regime. In order to clarify this situation, the effects of type of vegetation, species of grazer and grazing regime on the composition of the ground-dwelling arthropod fauna of partially improved heathland were determined. The effects of grazing by cattle or sheep and two grazing regimes (cattle or sheep, or both of them together with goats) were studied in eight plots (two replicates per treatment). Each plot included two types of vegetation, gorse (Ulex gallii)-dominated shrubland and improved grassland (Lolium perenne-Trifolium repens). Arthropods were surveyed using pitfall traps. Overall, the composition of the arthropod fauna did not differ between plots grazed by different species of grazer or using different grazing regimes but was significantly associated with the type of vegetation. Most of the opilionids and several carabids clearly preferred shrubland, while lycosids and various carabids were mainly associated with grassland. While the species of grazer affected the faunal composition of grassland, grazing regime was more important in shrubland. Arthropod responses to the grazing treatments were determined by the grazing behaviour of the large herbivores and the habitat requirements of each arthropod taxon. The great structural heterogeneity of the vegetation and the more microhabitats in shrubland grazed by mixed flocks was mainly a result of the goats preferring to browse on the woody vegetation in these areas. The grazing by either sheep or cattle had less of an affect on the fauna of shrubland than grassland.