Erigone Atra Research Articles

Spiders (Araneae) from three human-influenced habitats in the Golsfjellet mountain area, central southern Norway

Three sites at 900 m a.s.l. in the sub-alpine mountain birch forest region and under different levels of human-influence were investigated. Site 1: An open birch forest with some scattered spruces, a rich bush and field layer and a rich moss cover; very little grazed. Site 2: Tree and bush layer removed, a rich field layer invaded by open area species and some ’culture indicators’; there was a rich moss cover. Site 3: Grazed; tree layer, bush layer and moss cover absent. Pitfall trapping (18 May – 18 Aug. 2000) in site 1 - 3 resulted in 48, 48 and 22 spider species (in total 64 species). In site 1 and 2 Pardosa riparia (C.L.Koch, 1833) and Alopecosa pulverulenta (Clerck, 1757) were dominating. P. sphagnicola (Dahl, 1908) was also fairly common in site 1, P. palustris and P. hyperborea (Thorell, 1872) in site 2. Site 3 was almost completely dominated by Pardosa palustris (73.2 %) and Erigone atra Blackwall, 1841 (18.2 %); present (absent elsewhere) were also some specimens of Oedothorax retusus (Westring, 1851) (4.6 %).

Applying a biocomplexity approach to modelling farmer decision‐making and land use impacts on wildlife

Abstract The biocomplexity approach refers to a fully integrated social‐ecological systems (SES) simulation that represents bidirectional feedbacks between social and ecological components. This method is essential to accurately assess impacts of economy and policy on SES such as agroecosystems, where feedbacks between the drivers and impacts of cropping changes need to be simulated. Here we exemplify the biocomplexity approach using energy maize, which is becoming an important source of bioenergy in Europe, and thus, might cause a significant change in land use with knock on‐effects for wildlife. The integrated simulation tool consisted of a farmer decision‐making agent‐based model fully coupled to the Animal Landscape and Man Simulatin System (ALMaSS), an agent‐based simulation system for predicting impacts of land use on a range of Danish wildlife species: the brown hare (Lepus europaeus), the grey partridge (Perdix perdix), the skylark (Alauda arvensis), a carabid beetle (Bembidion lampros), a linyphiid spider (Erigone atra) and the field vole (Microtus agrestis). This was used to assess the impacts of increasing demand on energy maize on the six animal species. Two types of experimental scenarios were evaluated, with and without feedback between the social and ecological system. The assessment of species responses was based on changes in population size, abundance and occupancy. The response to the cultivation of energy maize was negative for three vertebrate species (skylark, hare and field vole) and positive for partridge and the two invertebrate species. The feedback scenarios showed that the incorporation of information from ecological system to the farmer decision‐making affected both a trend in area cultivated with energy maize as well as the animal responses. Synthesis and applications. Fully coupling agent‐based decision‐making and environmental simulation allows a detailed representation and integration of both social and ecological components of agricultural systems at proper spatial and temporal scales as well as of dynamic feedbacks between the two systems. By employing easy to interpret measures of changes in abundance and spatial occupancy of animal species, the simulation results could inform and simplify decision‐making on expected impacts of economy and policy regulations on wildlife.

Aerial dispersal activity of spiders sampled from farmland in southern England

Spiders can suppress populations of some important crop pests. Although dispersal is essential to their survival in the disturbed farmland environment, accounts of their dispersal activity over several seasons are few. Spiders dispersing across a landscape of mixed farmland were sampled over an 18-month period using Stick, Net and Bottle traps (SNB traps). Traps were located in a two year old grass ley where ground densities of spiders and wind speed data were also recorded. SNB traps were effective at sampling large numbers of dispersers; Linyphiidae were the most abundant family sampled (93%). Numbers of adult linyphiids dispersing were found to increase in autumn and winter with dispersal activity occurring frequently throughout the study period. Dispersal patterns were similar for congeners (Erigone spp., Oedothorax spp.) although differences were evident between common agrobiont species. Weather conditions associated with stable high-pressure systems appeared important for stimulating mass dispersal in Oedothorax Bertkau, 1883 species. Erigone atra Blackwall, 1833 dispersed more frequently and under more variable conditions. Winter and spring dispersal was low for adult Tenuiphantes tenuis (Blackwall, 1852) and Bathyphantes gracilis (Blackwall, 1841) compared to common erigonids. Ground populations correlated positively with dispersing spiders for some species indicating that dispersal activity was in part a function of population size. For Oedothorax fuscus (Blackwall, 1834) it is suggested that life history traits and weather conditions may interact to influence the sex ratio of dispersers over time.

Dispersal behavior in agrobiont spiders (Linyphiidae) — differential response to a wind chamber

Two species of common, farmland-inhabiting money/dwarf spider, Erigone atra Blackwall, 1833 and Oedothorax fuscus (Blackwall, 1834), were exposed to light wind conditions within a wind chamber to determine their propensity to exhibit dispersal behaviors over a nine-month period. A novel design of wind chamber, incorporating two tangential fans, produced a wide outflow thereby allowing behaviors to be expressed over a relatively large test area (1 m × 0.65 m). Sticks placed at 3 cm intervals in an undulating foam surface structurally mimicked a natural field setting. Whereas the majority of E. atra expressed dispersal and related behaviors (tiptoe and drop posture and ballooning) in every month testing occurred, corresponding behaviors were rarely recorded in O. fuscus. Results are discussed in relation to knowledge of the dispersal activity of O. fuscus in the field and factors which may influence dispersal frequency and initiation.

Parasitism of Trombidium brevimanum larvae on agrobiont linyphiid spiders from Germany

An experiment on three differently-managed agricultural fields in Ahlum, Germany, which aimed at establishing the impact of different management systems on the biodiversity of predators and decomposers, yielded a significant number of spiders parasitized by larvae of Trombidium brevimanum (Actinotrichida, Parasitengona, Trombidiidae). Spider data from the whole sampling period (September 2010-July 2012), indicated that ectoparasitic larvae were recorded only on spiders in pitfall traps in the period of June-July 2011. In this period, only eight species of Linyphiidae--out of 42 species assigned to nine spider families recorded from the study area--were parasitized by mites; considerable levels of parasitism were recorded on Erigone atra, E. dentipalpis, and Oedothorax apicatus. The highest prevalence of parasitism was recorded on the organic field for E. atra (29%), while on the integrated and conventional fields significantly fewer parasitized spiders were observed. The preferred attachment sites on the spider host were regions with softer cuticle, especially regions on the carapace and on the abdomen, adjacent to the pedicel.

Abundance and diversity of spiders (Araneae) in barley and young leys

The fauna of surface-active spiders was studied in 12 cereal fields, with two types of subcrop, and in four young (17 months old) perennial leys (grass/clover). The fields were located in the southeastern (A), central (B) and western (C) parts of Norway. In total, 3945 spiders were caught from May to September 2004, using pitfall traps. Linyphidae was the most numerous family, with Erigone atra Blackwall 1833 representing 56% of all trapped individuals. The total numbers of spider species and individuals were significantly higher in leys than in barley at sites where both crops were present (sites A and B), with on average 11 species and 93 specimens in barley, and 20 species and 393 specimens in leys. Thus, young perennial leys appeared to provide a better habitat for spiders than did cereal fields, as has previously been documented for older perennial leys. The use of multi-species crops instead of a single crop species undersown in cereals, tended to result in higher spider species diversity, but it did not influence the total number of specimens. An ordination (DCA) showed a clustering of the spider fauna from the same site, but no clear separation between main crop types (ley vs. barley) was apparent. The main crops, subcrops, and the surrounding environs of the cropped field seem to affect the diversity and abundance of spiders.

Novel management to enhance spider biodiversity in existing grass buffer strips

Grass buffer strips have been widely sown to mitigate against intensive agricultural management practices that have negatively impacted on invertebrate and plant biodiversity in arable farming systems. Typically, such strips are floristically species poor and are dominated by grasses. In the present study, we developed management practices to enhance the floristic and structural diversity of these existing strips for the benefit of spiders, a key provider of natural pest control in crops. Across three UK arable farms, we investigated the benefits of: (i) scarification to create germination niches into which wildflower seeds were sown and (ii) the effect of graminicide applications to suppress grass dominance. Spiders were sampled twice per year (July and September) during 2008 and 2009. The combination of scarification with wildflower seeds, as well as graminicide, resulted in the greatest wildflower cover and lowest grass cover, with a general trend of increased abundance of adult and juvenile spiders. The abundance of Pachygnatha degeeri, Bathyphantes gracilis and juvenile wolf spiders of the genus Pardosa was positively correlated with wildflower cover, probably reflecting increased prey availability. Sward structure was negatively correlated with Erigone atra, Oedothorax fuscus and juvenile Pardosa abundance. Management that utilizes existing commonly adopted agri-environment options, such as grass buffer strips, represents a potentially important conservation tool for increasing the quantity and quality of invertebrate habitats. This can maximize opportunities for the provision of multiple ecosystem services, including pest regulation by predators such as spiders. These management practices have the potential to be incorporated into existing U.K. and European agri-environment schemes.

애접시거미아과(거미목: 접시거미과)의 거미 1 신종과 4 한국미기록종의 기재

Five erigonine spider species are described with illustrations: a new species, Saitonia pilosus n. sp., and four records new to the Korean spider fauna, Ceratinella brevis (Wider, 1834), Erigone atra Blackwall, 1833, Maso sundevalli (Westring, 1851), and Parasisis amurensis Eskov, 1984. The occurrences of four spider genera, Ceratinella Emerton, 1882, Maso Simon, 1884, Parasisis Eskov, 1984, and Saitonia Eskov, 1992, are also new to Korea.

Biodiversity and the mitigation of climate change through bioenergy: impacts of increased maize cultivation on farmland wildlife

The public promotion of renewable energies is expected to increase the number of biogas plants and stimulate energy crops cultivation (e.g. maize) in Germany. In order to assess the indirect effects of the resulting land-use changes on biodiversity, we developed six land-use scenarios and simulated the responses of six farmland wildlife species with the spatially explicit agent-based model system ALMaSS. The scenarios differed in composition and spatial configuration of arable crops. We implemented scenarios where maize for energy production replaced 15% and 30% of the area covered by other cash crops. Biogas maize farms were either randomly distributed or located within small or large aggregation clusters. The animal species investigated were skylark (Alauda arvensis), grey partridge (Perdix perdix), European brown hare (Lepus europaeus), field vole (Microtus agrestis), a linyphiid spider (Erigone atra) and a carabid beetle (Bembidion lampros). The changes in crop composition had a negative effect on the population sizes of skylark, partridge and hare and a positive effect on the population sizes of spider and beetle and no effect on the population size of vole. An aggregated cultivation of maize amplified these effects for skylark. Species responses to changes in the crop composition were consistent across three differently structured landscapes. Our work suggests that with the compliance to some recommendations, negative effects of biogas-related land-use change on the populations of the six representative farmland species can largely be avoided.

Selective integration advantages when transience is costly: immigration behaviour in an agrobiont spider

Dispersal, and especially movement between the natal and the new environment, is a costly process. Costs are incurred not only during the preparation or transfer phase but also on arrival in a new environment. Such costs comprise, for instance, time costs because of the need to search for a suitable microhabitat or integration costs when immigration occurs in already densely populated habitat. The failure to settle or to integrate may consequently inflate the costs already incurred during emigration and transfer. Therefore, we expect emigrating individuals to have evolved enhanced integration capacities. In our laboratory experiments, dispersive phenotypes of the agrobiont spider Erigone atra were characterized by (1) faster settlement in empty habitat and (2) increased willingness to compete for ownership of already occupied sites. These correlated behaviours point to dispersive phenotypes (1) being likely to experience a selective advantage at settlement and (2) not being a random subsample from the population. These correlated behaviours are predicted to have a strong impact on spatial population dynamics and gene flow.

The Effects of Landscape Modifications on the Long-Term Persistence of Animal Populations

BackgroundThe effects of landscape modifications on the long-term persistence of wild animal populations is of crucial importance to wildlife managers and conservation biologists, but obtaining experimental evidence using real landscapes is usually impossible. To circumvent this problem we used individual-based models (IBMs) of interacting animals in experimental modifications of a real Danish landscape. The models incorporate as much as possible of the behaviour and ecology of four species with contrasting life-history characteristics: skylark (Alauda arvensis), vole (Microtus agrestis), a ground beetle (Bembidion lampros) and a linyphiid spider (Erigone atra). This allows us to quantify the population implications of experimental modifications of landscape configuration and composition.Methodology/Principal FindingsStarting with a real agricultural landscape, we progressively reduced landscape complexity by (i) homogenizing habitat patch shapes, (ii) randomizing the locations of the patches, and (iii) randomizing the size of the patches. The first two steps increased landscape fragmentation. We assessed the effects of these manipulations on the long-term persistence of animal populations by measuring equilibrium population sizes and time to recovery after disturbance. Patch rearrangement and the presence of corridors had a large effect on the population dynamics of species whose local success depends on the surrounding terrain. Landscape modifications that reduced population sizes increased recovery times in the short-dispersing species, making small populations vulnerable to increasing disturbance. The species that were most strongly affected by large disturbances fluctuated little in population sizes in years when no perturbations took place.SignificanceTraditional approaches to the management and conservation of populations use either classical methods of population analysis, which fail to adequately account for the spatial configurations of landscapes, or landscape ecology, which accounts for landscape structure but has difficulty predicting the dynamics of populations living in them. Here we show how realistic and replicable individual-based models can bridge the gap between non-spatial population theory and non-dynamic landscape ecology. A major strength of the approach is its ability to identify population vulnerabilities not detected by standard population viability analyses.

Information use and density-dependent emigration in an agrobiont spider

Density of conspecifics is considered as one of the main conditions affecting dispersal behavior and leading to a stabilization of population dynamics. Density-dependent dispersal can be induced by local competition at different phases during development and/or by density-related sources of social information. Here, we assessed the importance of population density on emigration rates and the degree to which the presence of silk threads at dispersal takeoff locations affects immediate dispersal decision making in the spider Erigone atra. By quantifying behaviors in wind tunnels under standardized laboratory conditions, silk-assisted long- and short-distance dispersal is quantified before the actual onset of the dispersal event. Increased densities during juvenile development only affected short-distance dispersal behavior. In females, short-distance dispersal increased with the female density experienced during development, whereas responses in males increased under combined high male/low female-experienced densities. Elevated densities at the onset of dispersal led to a general increase of predispersal behaviors. The presence of silk threads at takeoff platforms similarly induced an increase of dispersal displays, with specifically an increase in long-distance dispersal in both sexes. Our results demonstrate that the spider E. atra uses information related to density during development, most probably to avoid competition by performing short-distance dispersal. In contrast, density-related cues at the time of dispersal (i.e., increased densities and the presence of silk threads) increase general dispersal activities and long-distance ballooning events. Short- and long-distance dispersal strategies are consequently guided by differential density-related information use. Key words: araneae, density, dispersal, information, silk. [Behav Ecol]

Invertebrate biodiversity affects predator fitness and hence potential to control pests in crops

Natural enemies that control pests usually allow farmers to avoid, or reduce, the use of pesticides. However, modern farming practices, that maximize yields, are resulting in loss of biodiversity, particularly prey diversity. Does this matter? Pests continue to thrive, and without alternative prey the predators should, perforce, concentrate their attentions upon the pests.We showed that a diverse diet significantly enhances predator fecundity and survival. Experiments were conducted using common generalist predators found in arable fields in Europe, the carabid beetle Pterostichus melanarius (Coleoptera: Carabidae) and the linyphiid spider Erigone atra (Araneae: Linyphiidae). We tested the hypothesis that mixed species diets were optimal, compared with restricted diets, with respect to parameters such as predator weights, egg weights, numbers of eggs laid, egg development times, egg hatching rates and predator survival. In carabids, an exclusive earthworm diet was as good as mixed diets containing earthworms for egg production and hatching, but less good than such mixed diets for increase in beetle mass and sustained egg laying. For spiders, aphids alone (Sitobion avenae) or with the Collembola Folsomia candida, drastically reduced survival. Aphids plus the Collembola Isotoma anglicana improved survival but only aphids with a mixed Collembola diet maximized numbers of hatching eggs.Predators offered only pests (slugs or aphids) had lowest growth rates and fecundity. We therefore demonstrated that conservation of a diversity of prey species within farmland, allowing predators to exploit a diverse diet, is essential if predators are to continue to thrive in crops and regulate agricultural pests.

Microbial modification of host long-distance dispersal capacity

BackgroundDispersal plays a key role in shaping biological and ecological processes such as the distribution of spatially-structured populations or the pace and scale of invasion. Here we have studied the relationship between long-distance dispersal behaviour of a pest-controlling money spider, Erigone atra, and the distribution of maternally acquired endosymbionts within the wider meta-population. This spider persists in heterogeneous environments because of its ability to recolonise areas through active long-distance airborne dispersal using silk as a sail, in a process termed 'ballooning'.ResultsWe show that there is spatial heterogeneity in the prevalence of two maternally acquired endosymbiont infections within the wider E. atra meta-population and we demonstrate through several independent approaches a link between the presence of one of these endosymbionts, Rickettsia, and the tendency for long-distance movement.ConclusionThis novel finding that particular endosymbionts can influence host dispersal is of broad importance given the extremely widespread occurrence of similar bacteria within arthropod communities. A bacterial phenotype that limits dispersal has the potential not only to reduce gene flow and thus contribute to degrees of reproductive isolation within species, but also to influence species distribution and thus overall community composition.

Ballooning of spiders (Araneae) in Switzerland: General Results from an Eleven-Year Survey

A survey of ballooning spiders was carried out over a period of eleven years between 1994 and 2004. Altogether, 15,398 ballooning spiders, representing 103 species and 16 families, were caught with a 12.2 m high suction trap in an agricultural landscape of Switzerland. The families Linyphiidae, Araneidae, Philodromidae and Theridiidae were numerically dominant. Linyphiids represented 60% of the total, and were the most diverse family. Of the total captures, 31% were adults, and 52% of the adults were females. The diversity of species caught as males (78) was higher than that of females (68).We observed 11 species frequently ballooning: Meioneta rurestris, by far the most frequent, Araeoncus humilis, Erigone dentipalpis, Porrhomma microphthalmum, Erigone atra, Tenuiphantes tenuis, Nuctenea umbratica, Bathyphantes gracilis, Eperigone trilobata, Mangora acalypha and Oedothorax apicatus. Of the 103 species recorded, 28 species (27%) and two genera had not previously been recorded in ballooning studies, and 22 species are rare in Switzerland. Although the proportions of species from open areas and from areas with bushes and trees were almost identical, the proportion of individuals of species from open areas was much higher; 46% were ground-living species and the others were from higher vegetation layers.Dispersal by ballooning showed two main peaks: the first between the end of May and mid-August and the second from the beginning of October until the beginning of November. The maximal diversity was found in June (34 species). The percentage of adults varied between 12 and 65% during the year. The percentage of adult females varied between 32 and 100%. Phenological patterns for the main families are presented.

The effects of spatial and temporal heterogeneity on the population dynamics of four animal species in a Danish landscape

BackgroundVariation in carrying capacity and population return rates is generally ignored in traditional studies of population dynamics. Variation is hard to study in the field because of difficulties controlling the environment in order to obtain statistical replicates, and because of the scale and expense of experimenting on populations. There may also be ethical issues. To circumvent these problems we used detailed simulations of the simultaneous behaviours of interacting animals in an accurate facsimile of a real Danish landscape. The models incorporate as much as possible of the behaviour and ecology of skylarks Alauda arvensis, voles Microtus agrestis, a ground beetle Bembidion lampros and a linyphiid spider Erigone atra. This allows us to quantify and evaluate the importance of spatial and temporal heterogeneity on the population dynamics of the four species.ResultsBoth spatial and temporal heterogeneity affected the relationship between population growth rate and population density in all four species. Spatial heterogeneity accounted for 23–30% of the variance in population growth rate after accounting for the effects of density, reflecting big differences in local carrying capacity associated with the landscape features important to individual species. Temporal heterogeneity accounted for 3–13% of the variance in vole, skylark and spider, but 43% in beetles. The associated temporal variation in carrying capacity would be problematic in traditional analyses of density dependence. Return rates were less than one in all species and essentially invariant in skylarks, spiders and beetles. Return rates varied over the landscape in voles, being slower where there were larger fluctuations in local population sizes.ConclusionOur analyses estimated the traditional parameters of carrying capacities and return rates, but these are now seen as varying continuously over the landscape depending on habitat quality and the mechanisms of density dependence. The importance of our results lies in our demonstration that the effects of spatial and temporal heterogeneity must be accounted for if we are to have accurate predictive models for use in management and conservation. This is an area which until now has lacked an adequate theoretical framework and methodology.

Dominant insectivorous polyphagous predators in winter wheat: High colonization power, spatial dispersion patterns, and probable importance of the soil surface spiders (Araneae)

Spiders inhabiting the soil surface of a winter wheat field were examined using pitfall traps near Zurich, central Europe. The soil surface spider community was dominated by two species of wolf spiders Pardosa agrestis (Westring) and Pardosa palustris (L.) (Lycosidae) and three species of sheet-web weavers Erigone atra (Blackwall), Erigone dentipalpis (Wider) and Oedothorax apicatus (Blackwall) (Linyphiidae). The identity and average number of spiders collected in the traps over time between field border and center were compared revealing that the number of wolf spiders on the border did not differ significantly from the center. However, the sheet-web weavers expressed a consistent trend of slightly greater numbers in the field's center compared to the border. Computation of the dispersion index (after Morisita) indicates aggregated patterns throughout the field for both Lycosidae and Linyphiidae caught in the pitfall traps. The combined number of spider individuals showed an overall increase as the season progressed. Over 12000 spiders were collected from the 2 ha winter wheat field by means of 45 (7 cm diam.) pitfall traps in less than 3 months, whereby this high number is providing additional evidence for previous work reported in the literature of winter wheat field colonization by large numbers of spiders. The capacity of soil surface spiders to build up these high numbers, potentially consuming field crop insect pests at elevated rates suggests that they may play a significant role as natural control agents. The effectiveness of these spiders as natural enemies may be limited only by their apparently low feeding frequency reflecting a low rate of metabolism.

Microcosm studies on control of aphids by generalist arthropod predators: Effects of alternative prey

Generalist predators are potential controlagents of aphids in cereal fields. Becauseaphids are low-quality prey for most generalistpredators, the availability of alternativehigh-quality prey may influence theinteractions between aphids and their predatorsby reducing the predation rate due to loweredpreference for aphids. We analysed this bytesting the ability of six generalist predators(the spiders Erigone atra (Bl.), Clubiona lutescens (Westr.)/reclusaO.P.-C., Pachygnatha degeeri Sundevall,Pardosa prativaga (L.Koch), the carabidbeetle Bembidion lampros (Herbst), andthe harvestman Oligolophus tridens (C.L.Koch)) to suppress Rhopalosiphum padi(Linne) populations in the presence orabsence of alternative prey types (fruit fliesDrosophila melanogaster (Meigen) or thecollembolan Tomocerus bidentatus(Folsom)). Experiments of 10 days duration werecarried out in a microcosm set-up. Withoutalternative prey all predators except B.lampros were able to reduce aphid populationdevelopment significantly relative topredator-free controls. The harvest spider O. tridens was the most efficient predator(<90% reduction). Presence of alternativeprey (fruit flies) had a significant negativeeffect on aphid limitation by P. prativagaand a weak positive effect in B. lampros, but did not influence the ability to reduce aphids in E. atra, Clubiona, P. degeeri and O. tridens. In addition, 24-hours' consumption experiments with adult P. degeeri and subadult C. lutescens/reclusa, using R. padi and D. melanogaster as prey types, showed markedly lower consumption rates of aphid than of fruit fly prey. The microcosm arrangement is a simple way to partly simulate the habitat complexity of an agricultural field under laboratory conditions and proved to be a useful tool for investigating complex predator-prey interactions.

Prey to predator transfer of enriched 15N‐contents: basic laboratory data for predation studies using 15N as marker

AbstractAs an alternative to methods currently used to study predation under field conditions, we propose to mark prey with 15N, and to subsequently trace this label in the food chain. Preliminary laboratory work to develop this method is presented. The 15N‐content of polyphagous predators that have ingested 15N‐marked aphids was analysed with respect to: time after ingestion, the number of ingested 15N‐aphids, ingestion of additional non‐marked prey, and predator size. Increased 15N‐contents were detected in solid feeders [Platynus dorsalis (Pontopiddan), Coleoptera: Carabidae], as well as in fluid feeders [Erigone atra (Blackwall), Araneae: Linyphiidae] up to 11 days after ingestion. The increased 15N‐levels were constant over time from a few days after 15N‐ingestion onwards, and correlated with the number of ingested 15N‐aphids. The ingestion of additional non‐marked prey had no statistically significant influence on the predators’15N‐contents. The 15N‐contents of carabid species with varying biomasses could be compared directly. Our results are compared with literature data of other methods (e.g., ELISA).

The role of perennial habitats for Central European farmland spiders

Abstract Spiders are important predators of insect pests. Some species invariably dominate spider communities in crop fields over large parts of Europe, and are therefore considered as “agrobionts”. It is however not clear if these species generally prefer arable habitats, or to what degree they utilize other habitats during times when crops are inhospitable. Here, spider abundances in 26 crop fields and 16 perennial habitats in Germany were compared during spring. Overall spider abundance in winter wheat was 75% lower than in perennial habitats, and species richness was reduced by 46%. Out of a total of 91 species, 73 had higher densities in perennial habitats, including the most dominant crop spiders Erigone atra and Tenuiphantes tenuis. Only one species (Oedothorax apicatus) was significantly more abundant in crops than in perennial habitats. Hence, the high dominance of most “agrobiont” species in crops was due to low densities of other species, and not to their own higher abundances. Therefore, perennial habitats adjacent to crop-fields could enhance spider populations and their potential for biological control in arable fields on a landscape level.