Abundant Spider Species Research Articles

Spider diversity (Arachnida: Araneae) at Saurashtra University Campus, Rajkot, Gujarat during the monsoon

The present work deals with the diversity of spiders during the monsoon within the Saurashtra University Campus, Rajkot, Gujarat. A total of 38 species of spiders belonging to 32 genera and 14 families were recorded. Araneidae (25.81%) was found to be the most dominant family, with nine species from five genera. Guild structure analysis revealed seven feeding guilds, among all 31% most dominant feeding guilds represented by orb-web builders and stalkers, followed by ground runners (13%), irregular webs (10%), ambushers (7%), foliage hunters (6%), and space-web builders (2%). Ecological indices reveal high species richness (Margalef’s d = 8.97) and diversity (Shannon Index H’ = 3.526, Fisher alpha diversity α = 41.73). It concludes that the abundance of spider species at this study site was high and the evenness index was also high (e >0, e = 0.8944). These findings suggest the absence of stress elements in the study area.

Standardised inventories of spiders (Arachnida, Araneae) on touristic trails of the native forests of the Azores (Portugal).

BackgroundThe sharp increase in tourist visitation of the Azores Archipelago from 2015 onwards raised concerns about the impacts of recreational tourism on native habitats. In response, a project was financed by the Azorean Government to investigate the drivers of biodiversity erosion associated with recreational tourism. Here, we present the data on spider biodiversity found on trails located within the native Azorean forests as they are home to several endemic species of great conservation value. We applied an optimised and standardised sampling protocol (COBRA) in twenty-three plots located in five trails on Terceira and São Miguel Islands and assessed diversity and abundance of spider species at different distances from the trail head and the trail itself.New informationOf the 45 species (12435 specimens) collected, 13 were endemic to the Azores (9690 specimens), 10 native non-endemic (2047 specimens) and 22 introduced (698 specimens). This database will be the baseline of a long-term monitoring project for the assessment of touristic impacts on native forest trails. This methodology can also be used on other habitats and biogeograhical regions.

Tussock Circumference, Land Use Type and Drought Variably Influence Spider Assemblages Associated with Hyparrhenia hirta Grass Tussocks

Many human activities have an impact on the fauna and flora of the South African Grassland Biome, including agriculture, fire and urbanisation. Disturbances in grassland habitats often result in Hyparrhenia hirta, a native pioneer grass species, establishing dense stands. Here the assemblage composition, species richness and abundance of spiders associated with H. hirta tussocks was investigated at three grassland sites (annually burnt, suburban local road traffic and undisturbed control) in the central Free State Province of South Africa during winter 2015 and 2016. Further, inter-annual differences during a period of intense drought were evaluated. An increase in spider species richness, abundance and different assemblage composition with increased tussock height and basal circumference was expected, and we predicted these effects would differ between land use types. Overall, Tibellus spp. immatures (Philodromidae) and Poachelas striatus Haddad & Lyle, 2008 (Trachelidae) were the most abundant spider species, while Philodromidae and Gnaphosidae were the most abundant spider families at all three sites during both years. The most species-rich families were Gnaphosidae, Salticidae and Thomisidae. Over the two-year sampling period there was a significant decline in overall spider abundance (58.09 %) and species richness (28.17 %), which could be explained by the cumulative effects of a severe drought experienced in central South Africa during 2015 and 2016. Species richness and assemblage composition were influenced by tussock basal circumference and disturbance effects, but not by tussock height. Several species were associated with the control site, while certain diversity metrics of the burnt and road verge sites were more stable, pointing to the importance of primary productivity in the former and water in the latter, for spider diversity. Trade-offs related to disturbance need to be carefully considered when developing management strategies for biodiversity.

Variation in web-building spider communities among three tropical tree species in a young experimental plantation

Abstract We documented the presence and abundance of spider species (Arachnida: Araneae) on young trees of Swietenia macrophylla, Ceiba pentandra and Cordia dodecandra found in an experimental plantation. Surveys of spider abundance and species identity conducted twice during the growing season indicated marked differences in web-building spider assemblages associated with each tree species. Swietenia exhibited the lowest spider abundance, whereas Cordia and Ceiba had similarly higher abundances. Leucauge venusta (Walckenaer, 1841) was the dominant spider on all tree species, but different spider species were co-dominant on Cordia and Ceiba (Araneus pegnia (Walckenaer, 1841) and Argiope argentata (Fabricius, 1775) respectively), and several spider species were exclusive to each tree species. These results highlight the influence of tree species identity on community structure at higher trophic levels, particularly in the case of web-building spiders inhabiting tropical tree communities.

A cost‐efficient and simple protocol to enrich prey DNA from extractions of predatory arthropods for large‐scale gut content analysis by Illumina sequencing

Summary Molecular analysis of predator gut content is a popular tool to uncover food web structure and has greatly profited from the emergence of next‐generation sequencing technology. However, the molecular recovery of prey spectra comes with many challenges, particularly the overabundance of predator DNA in extractions. When predator and prey are distantly related, predator‐specific blocking primers can be used to preferentially amplify prey DNA. But this is difficult in the case of arthropods, where prey and predator are often closely related. Here, we present a simple and cost‐efficient protocol for high‐throughput analysis of the gut content of predatory arthropods without the need for blocking primers. We test several factors for their potential to enrich prey DNA from extractions of predators, including size selection of DNA, selection of different body parts for extraction, and variation in extraction lysis time and PCR fragment length. Using a locally abundant spider species (Hololena adnexa, Agelenidae), we show that prey DNA can be significantly enriched from predator extracts by selectively removing high molecular weight DNA and by extracting from the midgut and hindgut only. A comparison of our results with observational data from other agelenid spider species indicates a high efficiency of our approach. Our enrichment protocol allows for the parallel analysis of several hundred predators in a single MiSeq run, reducing the cost per specimen to only a few dollars and requiring a simple and minimal work flow. This will enable large‐scale and ecosystem‐wide analyses of niche differentiation and food web structure.

Diversity of grass-dwelling spiders (Arachnida: Araneae) in calcareous fens of the Coastal Lowland, Latvia

Calcareous fens have a high conservation priority in the European Union. They are very unique, very sensitive and very rare habitats in Latvia as well as in many other European countries. Because of their rarity, many organisms living in calcareous fens are nowadays considered threatened. The same is applied to spiders. Spiders have been suggested as good biodiversity indicators because they have numerous direct and indirect relationships with other organisms. Only few investigations have been carried out on fen inhabiting spiders. The knowledge of grass-dwelling spiders is especially lacking. Thus the aim of this study was to evaluate grass-dwelling spider diversity in several calcareous fens of Latvia, compare these fens and to find out the habitat features that might affect grass-layer inhabiting spiders. The research was carried out in eight calcareous fens located in the Coastal Lowland of Latvia. A total of 760 spiders from nine families and 20 species were collected with a sweep net. Two of the most abundant spider species were Dolomedes fimbriatus (Clerck, 1757) and Tibellus maritimus (Menge, 1875). Diversity indices suggested that the grass-dwelling spider community consists of few abundant species and numerous rare species. Correlation analysis as well as DCA showed that plant species diversity did not significantly affect spider species richness and diversity, although at the same time there were a lot of significant associations between spiders and individual plant species. It was shown that various spider species responded very differently to the presence of particular plant species, and thus habitat structural heterogeneity emerges to be an important factor influencing the grass-dwelling spider diversity and community structure. Correlation analysis also revealed that spider abundance was negatively affected by the vegetation height and wind speed.

Prediction of abundance of forest spiders according to climate warming in South Korea

Distribution of spiders will be changed as climate warms. Abundance of spider species was predicted nationwide in South Korea. Abundance of spiders was projected using temperature species distribution model based on a nationwide data (366 forest sites) according to climate change scenario RCP 4.5 and 8.5. The model predicts that 9 out of 17 species will increase in abundance while 8 species will decrease. Based on this finding, a qualitative prediction (increase or decrease) was conducted on the species with more than 1% occurrence: 68 species are expected to decrease, 9 to increase, and 8 to change a little. In pooled estimation, 76 species (75%) are expected to decrease, 18 species (18%) to increase, and by 8 species (8%) to have little change. The projection indicates that majority of spider species will decrease, but minority of species will increase as climate warms, suggesting great increase of remained species in lowlands.

Resident spiders as predators of the recently introduced light brown apple moth,Epiphyas postvittana

AbstractThe invasive light brown apple moth,Epiphyas postvittana(Walker) (Lepidoptera:Tortricidae), has not reached damaging levels on crops inCalifornia (USA), suggesting that its populations and impact are limited by generalist natural enemies. In a series of laboratory experiments, we examined resident spiders as predators ofE. postvittanalarvae on two host plants, the ornamentalAustralian tea tree,Leptospermum laevigatum(Gaertn.)F.Muell (Myrtaceae), and the weedFrench broom,Genista monspessulana(L.) L.A.S.Johnson (Fabaceae). Of three abundant spider species inAustralian tea tree, two hunting spiders measurably reduced the numbers ofE. postvittanalarvae and plant damage, whereas a web‐weaving spider had no detectable impact. The adult stage of the dominant hunting spiderAnyphaena apertaBanks (Anyphaenidae) consumedE. postvittanalarvae, but neither large nor small juveniles had statistically detectable effects on numbers of larvae. However, plant damage was reduced in the presence of large juvenileA. aperta, suggesting thatA. apertamay also have non‐consumptive effects on the feeding behavior ofE. postvittanalarvae.Anyphaena apertaconsumed larvae only when larval densities exceeded a low threshold in a functional response experiment, leading to a typeIIIfunctional response. AdultA. apertashowed no preference for differentE. postvittanainstars, whereasCheiracanthium mildeiL.Koch (Miturgidae), an abundant hunting spider onFrench broom, showed a partial preference for late‐instar larvae. The generalist feeding habits of the spiders may have precluded strong prey preferences. Results show that hunting spiders may help limitE. postvittanapopulations inCalifornia, and that they may in turn reduce the impact ofE. postvittanaon its host plants.

Short and long-term effects of three neurotoxic insecticides on biological and behavioural attributes of the orb-web spider Alpaida veniliae (Araneae, Araneidae): implications for IPM programs

Soybean pest control in Argentina is done just by chemical control using broad-spectrum pesticides. Alpaida veniliae (Araneae, Araneidae) is one of the most abundant spider species of the orb web weaver guild in soybean, and it is considered a very important polyphagous predator, attacking different insects' families. The objective of this study was to determine if neurotoxic insecticides commonly used in soybean crops and a new active ingredient registered in Argentina (spinosad) adversely affected survival, prey consumption, mating behaviour, web building and reproductive capacity of A. veniliae females, under standard laboratory conditions. Spinosad was the most harmful insecticide due to high acute toxicity, even at lower concentrations than those registered for its field use and for its sublethal effects also. Cypermethrin caused several sublethal effects although its acute toxicity on spider was lower than other insecticides. It reduced prey consumption, affected web building, caused abnormalities in eggs sacs and decreased drastically the fecundity and fertility at sublethal concentrations. Endosulfan did not reduce prey consumption but it affected web building, caused abnormalities in eggs sacs and egg masses, and decreased the fecundity and fertility. Spinosad was also the compound with the most drastic effect on web building, it did not reduce prey consumption and fecundity, but fertility was reduced and abnormalities in egg sacs and egg masses were observed. The use of these insecticides in IPM programs according to their potential toxicity on spider communities is discussed.

Sika deer browsing differentially affects web-building spider densities in high and low productivity forest understories

The effects of sika deer (Cervus nippon) browsing and understory productivity on web-building spiders' density were experimentally examined. We particularly focused on the nonlinear effects of these 2 factors and their underlying mechanisms. Our field experiments controlling deer density and understory productivity revealed that the deer affected the densities of 2 abundant spider species nonlinearly: the deer effect was unimodal or constant in lower productivity plots and negative in higher productivity plots. The nonlinear effects seemed to occur because the response trend of the spiders' limiting factors to deer impact differed between lower and higher productivity plots. In lower productivity plots, the density of the most abundant spider species, Prolinyphia longipedella, was limited by dicot cover, and both spider density and dicot cover had unimodal-shaped responses to deer density. This spider species was limited by the availability of twigs in higher productivity plots and responded negatively to deer density. Deer seemed to affect web-building spider density in understory vegetation by changing the number of available sites for webs through browsing. However, the precise limiting factors differed with understory productivity. Since forest understory productivity is expected to show large variation at various spatial scales due to differences in canopy tree density, the availability of nutrients, and other environmental factors, considering nonlinear effects is important when predicting the impact of large herbivores on invertebrates in forest understories.

Abundância de três espécies de aranhas (Araneae) em ecossistemas nativos e manejados no Rio Grande do Sul, Brasil

We assessed the abundance patterns of three theridiid species: Hetschkia gracilis (Keyserling 1886); Phycosoma altum (Keyserling 1886); and Thwaitesia affinis O.P.-Cambridge, 1882 in four habitats: Araucaria Forest (native forest) and plantations of A. angustifolia, Pinus spp., and Eucalyptus spp. in Floresta Nacional de Sao Francisco de Paula Reserve, southern Brazil. The plantation stands in the study system are managed by the selective cutting of adult trees, allowing longer rotation intervals. We collected spiders in 2003 and 2004 by beating the vegetation inside three replicates of each forest type. We performed a permanova to test whether there were differences on species abundances between habitats. We tested the influence of the stand sizes, distance between stands, and vegetation cover composition on each spider species abundance. Stands with higher vegetation cover of bushes and vines presented higher abundances of Hetschkia gracilis and Thwaitesia affinis . Phycosoma altum abundance did not respond to any explanatory variables. Results highlighted the importance of alternative management of plantation stands to enhance and maintain the understory vegetation diversity, which in turn support the spider populations. Key words: Araucaria Forest, Habitat structure, Pinus plantation, Eucalyptus plantation, Forest management.

Spatial distribution of spiders and epedaphic Collembola in an environmentally heterogeneous forest floor habitat

Describing the biotic and abiotic processes that are responsible for the formation of spatial patterns in predators and their prey is crucial for improving our understanding of food-web interactions. We studied the spatial distribution of four abundant spider species and three common groups of epedaphic Collembola prey in a beech-dominated (Fagus sylvatica) forest floor habitat and related the observed patterns to environmental heterogeneity, overall predator activity (all ground beetles and spiders) and prey availability (all Collembola) at the local scale. Spiders and epedaphic Collembola were sampled over 392 days in a spatially explicit design based on a regular grid of 25 pitfall traps (inter-trap distance 100 m). Environmental heterogeneity was characterized by cover of moss and litter as well as the amount of dead wood at each trap location. We first used the index of dispersion to characterize the spatial distribution of spider species and Collembola and then related the observed patterns to environmental heterogeneity, predator and prey availability while testing for spatial autocorrelation within the same models. All taxa were significantly more aggregated than expected from the assumption of random distribution. The distribution of spider species was positively (Coelotes terrestris) or negatively (Tenuiphantes zimmermanni and Tapinocyba insecta) related to the cover of moss and negatively related to litter cover (C. terrestris) or the local availability of prey (T. insecta). The distribution of Collembola was negatively related to local litter cover (Lepidocyrtus spp.) and positively related to the amount of medium deadwood pieces (all other Entomobryidae). Our study suggests that none of the spider species preferred areas of low overall predator activity density. Moreover, it does not indicate association of spider species to prey-rich areas at the analyzed scale of WO m. It further highlights the importance of environmental heterogeneity, as different habitat properties differentially affected the local activity density of spiders and Collembola and thus considerably contributed to the understanding of distribution patterns. (c) 2012 Elsevier GmbH. All rights reserved. (Less)

Short-Term Response of Soil Spiders to Cover-Crop Removal in an Organic Olive Orchard in a Mediterranean Setting

This study shows that disturbance caused by cover-crop removal (CCR) in an organic olive orchard affects ground-spider populations. The effect of CCR on various organic olive-orchard plots was assessed by monitoring the abundance and diversity of ground-dwelling spiders. Covered plots in the organic olive orchard were compared with uncovered plots where the covers had been removed mechanically. CCR positively affected the most abundant spider species Zodarion styliferum (Simon) (Araneae: Zodariidae) as well as other species of running spiders belonging to the families Gnaphosidae and Lycosidae. Over time, the two types of plots did not significantly differ in diversity or dominance. Similarly, no differences were detected between the study plots in terms of the distribution of individuals when a cluster-similarity analysis was performed. This lack of difference in diversity might be due to the spatial scale used in the study or climatology. Because of their general effects, CCR profoundly changed the abundance of spiders in the olive orchard, but with no clear impact on spider diversity.

Diversity of canopy and understorey spiders in north‐temperate hardwood forests

Abstract1 We characterized and compared diversity patterns of canopy and understorey spiders (Arachnida: Araneae) on sugar maple (Acer saccharum Marsh.) and American beech (Fagus grandifolia Ehrh.) in hardwood forests of southern Québec, Canada.2 We sampled canopies of 45 sugar maple and 45 American beech trees and associated understorey saplings in mature protected forests near Montréal. Samples were obtained by beating the crown foliage at various heights and by beating saplings around each tree.3 Eighty‐two species were identified from 13 669 individuals. Forty‐eight species and 3860 individuals and 72 species and 9809 individuals were collected from the canopy and the understorey, respectively.4 Multivariate analyses (NMDS ordination and NPMANOVA) showed the composition of canopy and understorey assemblages differed significantly, and canopy assemblages differed between tree species. Rank‐abundance distribution models fitted to the canopy and understorey data indicated that different mechanisms structure the assemblages in both habitats. Three abundant spider species were significantly more common in the canopy; ten species were collected significantly more often in the understorey.5 The forest canopy was shown to be an important reservoir for spider diversity in north‐temperate forests.

Habitat Islands, Forest Edge and Spring-active Invertebrate Assemblages

Forest management results in forest patches of varying sizes within a clearcut matrix. The result is a large amount of edge habitat and many small patches across the landscape. Here we describe the spring-active epigeal spider and carabid fauna found at the forest-clearcut edge of spruce forest in northern Ontario, Canada. We include two types of edge: the forest-clearcut interface and the small habitat patches formed by forest residuals within the clearcut. Spring-active forest spiders and carabids appear little affected by adjacent clearcutting activity, and some forest species, such as Agyneta olivacea (Emetron), Diplocentria bidentata (Emetron) and Microneta viaria (Blackwall), are more prevalent at the forested edge. Common and abundant spider species were equally recorded in forest interior and forest edge. Generally, no invasion of open-habitat species was observed within the forest, although smaller forest patches may be at higher risk.

Brown recluse spiders: A review of biology, life history and pest management

Members of the spider genus Loxosceles (Araneae: Sicariidae) are found throughout the world. Their venom can cause severe open necrotic lesions in humans that can take several months to heal. Bite victims may also develop systemic reactions that can be life-threatening if medical attention is delayed or unavailable. Many Loxosceles species establish large populations in human habitats, creating a threat to human health and safety. Loxosceles reclusa, the brown recluse spider, is by far the most abundant spider species in many homes throughout the south-central United States. There has been an increase in awareness of brown recluse spiders, primarily due to negative media coverage of disfiguring bites and immense, slow-healing wounds. Although the bite of L. reclusa has been identified as a cause of necrotic lesions for nearly five decades, surprisingly few studies examine the biology of these spiders, and none have examined their association with humans. Few data have been published on the killing efficacy of pesticides on L. reclusa. Although millions of dollars are spent each year to control populations of L. reclusa in homes, no studies have been conducted to test newly developed chemicals or examine the benefits of integrated pest management practices. Here, we review historical accounts of pest management for L. reclusa populations and previous laboratory studies of biology and behavior. We then discuss how current studies of urban ecology, biological control, and urban pest management contribute to the management of L. reclusa populations in human habitats.

DAY VS. NIGHT SAMPLING FOR SPIDERS IN GRAPE VINEYARDS

We compared day sampling (between 0700 and 1100) and night sampling (between 1900 and 2300) of spiders on grapevines in a California vineyard in 1993 and 1994, shaking spiders from the vines onto a drop cloth and vacuuming them up. Pooled density of the seven most abundant spider species did not differ significantly between day and night sampling, nor did density of Cheiracanthium inclusum (Miturgidae), Trachelas pacificus (Corrinidae), Oxyopes spp. (Oxyopidae) or Neoscona oaxacensis (Araneidae). Under day sampling Metaphidippus vitis (Salticidae) was 60% more abundant and Hololena nedra (Agelenidae) more than 2.5 fold more abundant than under night sampling. Daytime sampling generally resulted in a higher percentage of capture for each spider taxa analyzed, but neither of the diversity indices (Shannon-Wiener, Simpson or Bray-Curtis) showed any difference between day and night sampling. Parameters generated by Taylor's power law indicate a uniform distribution for most spider taxa, which was not affected by sampling time with the exception of H. nedra. We suggest that at vineyard sites in California with a similar spider community, sampling can be limited to daylight hours if a sampling method is used which is sufficiently vigorous to dislodge spiders from their resting places.

Changes in wolf spider (Araneae) assemblages across woodland–pasture boundaries in the central wheat‐belt of New South Wales, Australia

AbstractThe abundance of wolf spiders (Lycosidae) was measured across woodland–pasture boundaries in the wheat‐belt of New South Wales, Australia, to determine the nature and magnitude of any edge effect. Spiders were collected by spotlighting along sample plots in woodlands located at distances of 5, 20, 35 and 200 m from the edge, and along sample plots in paddocks located at distances of 5 and 20 m from the edge. The wolf spider assemblage changed significantly across the edge, but the difference could be accounted for only by a change between the woodland and the paddock and not by any changes within the woodland at different distances from the edge. Ground cover (wolf spider microhabitat) changed significantly between the paddock and the woodland, but there were no consistent differences in microhabitat with distance from edge within either paddocks or woodlands. There was a significant correlation between an ordination of sites based on spider species abundance and an ordination based on microhabitat variables, suggesting that the wolf spider assemblage was responding to differences in microhabitat. Fine‐scale selection of microhabitat by most wolf spider species was non‐random, with most species preferring locations with grass cover, rather than more open locations. The present study indicates that wolf spiders are mostly unaffected by edge conditions at the woodland–paddock boundary. Accordingly, small and/or linear remnants with high edge‐to‐area ratios may constitute suitable faunal habitat for wolf spiders and perhaps other terrestrial arthropod species, despite the fact that this configuration is unsuitable for many vertebrate species.

Comparison of Sampling Methods Used to Estimate Spider (Araneae) Species Abundance and Composition in Grape Vineyards

The effectiveness of 3 methods for sampling spiders in grape vineyards was tested. The sampling methods were as follows: (1) a drop-cloth method in which spiders were dislodged from a 5.1-m2 area of grapevine onto a drop cloth, (2) a funnel method in which spiders were dislodged into a 0.74-m2 funnel, and (3) a D-vac method in which 50 sections of grapevine (3D-em sections, total area of 5.4 m2 ) were suctioned with a gasoline-powered vacuum. Data from all sampling methods were adjusted for area sampled and compared with an absolute control, in which foliage from an entire vine was removed and searched for spiders. Analyses were made on the follOwing 8 most abundant spider species: Allyphaella pacifica Banks, Metaphidippus vitis (Cockerell), Theridion dilutum Levi and Theridion melanumm Hahn (grouped as Theridion spp.l, Cheiracanthiuminclusum (Hentz), Hololena nedra Cham­ berlin & Ivie, Trachelas pacificus (Chamberlin & Ivie), and Erigone dentosa (O.P.-Cambridge). Mean spider abundance from each sampling method differed Significantly from the absolute control in (::=1) speCies. The funnel method often overestimated spider abundance·while the drop-cloth and D-vac methods often underestimated spider abundance. Estimates of spider species composition were most accurately measured by the drop-cloth method and were sig­ nificantly altered by the D-vac method. We tested 3 data transformations (In(x + 1), V (x + 0.5), and x lbl2 ) to stabilize the variance and satisfY the requirements of analysis of variance (ANOVA). No single transformation uncoupled the mean and variance for all spider species over the 3 sampling methods. Using mean and variance of mean spider abundance, sample size and disperSion parameters were created by way of the Taylor power law. Sample sizes were determined for each sampling method; estimates of sample size and sampling costs varied considerably among spider species and sampling methods. All but 1 spider species collected with the drop-cloth method had a clumped distribution, the funnel method produced variable dispersion indexes, and all spider species collected with the D-vac method had a random distribution pattern. Whereas no Single sampling method was best for all spider species, the funnel method is favored because of its efficiency in estimating spider densities and its reduced cost. ABSTRACT The effectiveness of 3 methods for sampling spiders in grape vineyards was tested. The sampling methods were as follows: (1) a drop-cloth method in which spiders were dislodged from a 5.1-m2 area of grapevine onto a drop cloth, (2) a funnel method in which spiders were dislodged into a 0.74-m2 funnel, and (3) a D-vac method in which 50 sections of grapevine (30-cm sections, total area of 5.4 m2) were suctioned with a gasoline-powered vacuum. Data from all sampling methods were adjusted for area sampled and compared with an absolute control, in which foliage from an entire vine was removed and searched for spiders. Analyses were made on the following 8 most abundant spider species: Allyphaella pacifica Banks, Metaphidippus vitis (Cockerell), Theridion dilutum Levi and Theridion melanurum Hahn (grouped as Theridion spp.), Cheiracanthium inclusum (Hentz), Hololena nedra Cham- berlin & Ivie, Trachelas pacificus (Chamberlin & Ivie), and Erigone dentosa (O.P.-Cambridge). Mean spider abundance from each sampling method differed significantly from the absolute control in (2=1) species. The funnel method often overestimated spider abundance· while the drop-cloth and D-vac methods often underestimated spider abundance. Estimates of spider species composition were most accurately measured by the drop-cloth method and were sig- nificantly altered by the D-vac method. We tested 3 data transformations (In(x + 1), V (x + 0.5), and x1-bl2) to stabilize the variance and satisfY the requirements of analysis of variance (ANOVA). No single transformation uncoupled the mean and variance for all spider species over the 3 sampling methods. Using mean and variance of mean spider abundance, sample size and dispersion parameters were created by way of the Taylor power law. Sample sizes were determined for each sampling method; estimates of sample size and sampling costs varied considerably among spider species and sampling methods. All but 1 spider species collected with the drop-cloth method had a clumped distribution, the funnel method produced variable dispersion indexes, and all spider species collected with the D-vac method had a random distribution pattern. Whereas no single sampling method was best for all spider species, the funnel method is favored because of its efficiency in estimating spider densities and its reduced cost.

A spider population in flux: selection and abandonment of artificial web-sites and the importance of intraspecific interactions in Lephthyphantes tenuis (Araneae: Linyphiidae) in wheat.

Lepthyphantes tenuis, a small sheet-webbuilding linyphiid spider is one of the most abundant spider species of cereal fields in Europe. In the present study we examined the process of web-site selection and web-site tenacity by adult females of this species in a winter wheat field. Spiders were selective in their choice of web-site. Different immigration rates into various manipulated web-sites, in field and laboratory, suggested that structural support and suitable micro-climate (high humidity) are the most important factors in the selection. Small holes dug in the ground were the most favoured web-sites. Web-site occupation was influenced by the presence of other conspecific spiders. Territorial contests occurred between spiders attempting to occupy the same web, these almost invariably led to the take-over of the web when the intruder was heavier. Interference, but also a certain level of tolerance, between spiders within the same web-site but in different webs was suggested by direct and indirect evidence. Many holes supported two or even three spiders in vertically stratified webs. Leaving probability of marked spiders was significantly higher in multiply occupied holes than in holes with a single web. Comparison with the results of a no-interference stochastic model showed that multiple occupancy in nature is less frequent than predicted by the model. There was further evidence for weak extra-web-interference between spiders in that multiple occupancy was even less frequent and overall occupancy was lower in web-sites which were packed close to each other. However, a level of tolerance for crowding is shown by the fact that closely packed hole colonies supported a spider density 13 times higher than in natural web-sites in the field. A marking experiment was carried out to gain information on web-site tenacity (i.e. the length of time a spider spends in a web-site) and abandonment. The average duration of tenacity was less than 2 days. A random loss function gave a good fit to the tenacity distribution and suggested that spiders abandoned web-sites randomly with a fixed leaving probability of c. 0.5. Individual webs were often used consecutively by more than one spider, and some spiders built more than one web in the same web-site. Calculations showed that abandonment is the most frequent leaving mode, while take-over by contest between spiders and disappearance due to destruction were some-what less frequent and equally likely modes of ending tenacity. It is suggested that the apparent contradiction between the selectiveness and competitiveness of spiders for web-sites and the relatively short tenacity observed can be resolved by hypothesising that spiders leave websites soon because they apply the strategy of spreading risk: spiders by frequently moving from one web-site to another distribute their reproductive efforts across several localities. This hypothesis is further supported by changes in web-site preference and ballooning behaviour at the onset of the reproductive stage in L. tenuis.