Epigeic Spiders Research Articles

Influence of habitat and microhabitat on epigeal spider (Araneae) assemblages in four stand types

Studies based on presence=absence of a species may provide insight into habitat associations, allowing the distribution of species to be predicted across the landscape. Our objective was to characterise the epigeal spider fauna in three mature boreal forest types (conifer, mixedwood and deciduous) and a disturbed habitat (clearcut) to provide baseline data on the spider species inhabiting major forest types of boreal northwestern Ontario, Canada. Only spring-active epigeal spiders were considered for logistical reasons. We further identified the coarse woody debris structure and microhabitat characteristics within these stand types to try to refine our ability to predict the within-stand occurrence of spiders. We found the clearcut habitat strongly dominated by the Lycosidae with 55% of spiders represented by a single species, Pardosa moesta Banks. The forested habitats were more diverse, with web-building families forming a large component of the fauna and many species represented by only a few individuals. The spider com- position of the deciduous stands (aspen and mixedwood) was very similar, and distinct from that of spruce stands. Species such as Agroeca ornata (Emerton) (Liocranidae) and Pirata montanus Emerton (Lyco- sidae) were strongly associated with deciduous leaf litter. Within the spruce stands, Agyneta olivacea (Emerton) (Linyphiidae) and Pardosa uintana Gertsch (Lycosidae) were associated with feathermoss rather than Sphagnum microhabitats. Many of the habitat associations observed at Rinker Lake do not conform well to those described in the taxonomic literature as typical for the species. Few associations with coarse woody debris or microhabitat attributes (other than ground cover type) were found.

Change in the community of epigeal spiders and harvestmen (Araneae, Opiliones) with the age of an apple orchard

Change in the community of epigeal spiders and harvestmen (Araneae, Opiliones) was studied in an experimental apple orchard for six consecutive years. Five plots were surveyed by pitfall traps. Four of the plots were young (1–4 years); one plot was older (15–20 years). The abundance of epigeal arachnids increased with the age on the young plots, while it was constant on the older plot. There were significantly more arachnids on the young plots than on the older one. In turn, the diversity was significantly lower on the young than on the older plots. Lycosidae, Phalangiidae and Tetra-gnathidae dominated the young plots. The older plots were richer in Agelenidae, Clubionidae, Dysderidae, Gnaphosidae, Linyphiidae, Pisauridae and Salticidae. Principal species of the young and older plots were identified using multivariate analysis.

Effects of low-input farming systems on carabids and epigeal spiders – a paired farm approach

We compared the effects of different low-input farming systems on carabids and spiders. The study was performed in a 3-year field survey using a paired-farm approach in six different landscapes units in northwestern Switzerland considering also the nearby semi-natural habitats. Carabids and spiders were sampled in 24 winter cereal crops and 18 semi-natural habitats using five funnel pitfall traps per site. Considering all cereal sites, in low-input ICM fields (= no insecticides, fungicides and growth regulators; ICM: Integrated crop management) 36% less carabids and 8% less spider specimens were found. In several cases, carabid populations of organic fields were significantly richer in species and abundance than in the low-input integrated crop management farmed plots. Endangered, stenoceous carabids (e.g. xero-thermophilous) and top-predators were more abundant in the organic fields. Spider communities differed less in mean number of species and abundance between the two low-input agricultural systems. Multivariate analysis showed that farming method and weed abundance were significant factors altering the carabid fauna and weed diversity influence spider fauna. Wolfspiders such as Pardosa agrestis, P. palustris and Trochosa ruricola seem to be enhanced by organic management. Linyphiids (Erigone atra, Oedothorax apicatus) were more abundant in lowinput ICM fields. Several carabid species and wolfspiders which have their main distribution in semi-natural habitats occurred more abundant in organic fields. This indicates that seminatural habitats in combination with organic farming may be an important factor for the conservation and enhancement of the species rich assemblages on agricultural land. Auswirkungen von zwei extensiven Anbausystemen auf die Laufkafer- und Spinnenfauna wurden unter Berucksichtigung der im Umfeld liegenden naturnahen Habitate untersucht. Sechs vergleichbare Paarbetriebe in sechs Landschaften der Nord-Westschweiz wurden wahrend einer 3-jahrigen Untersuchung dazu ausgewahlt. Die epigaischen Nutzarthropoden wurden mittels 5 Trichterbodenfallen in 24 Wintergetreideflachen und 18 naturnahen Flachen erfasst. Uber alle Ackerstandorte betrachtet wurden in den extensiv, integriert (IP) bewirtschafteten Getreideflachen (keine Anwendung von Fungiziden, Insektiziden und Wachstumsregulatoren) 36% weniger Laufkafer und 8% weniger Spinnentiere gefunden. In einigen Vergleichsfallen waren die durchschnittliche Artenvielfalt und Aktivitatsdichte der Laufkafer in den biologisch bewirtschafteten Wintergetreideflachen signifikant hoher als in den IP-Extenso Flachen. Gefahrdete, stenoke (z.B. xero-thermophile) Laufkaferarten und Top-Pradatoren waren in den biologisch bewirtschafteten Flachen zahlreicher. Bei der Spinnenfauna ergaben sich weniger deutliche Unterschiede betreffend durchschnittlicher Artenzahl und Aktivitatsdichte. Multivariate Analysen zeigten, dass die Anbaumethode und die Dichte der Begleitflora die Laufkafer signifkant beein

The effects of wildfire on ground‐active spiders in deciduous forests on the Swiss southern slope of the Alps

Summary The influence of fire upon biodiversity has been investigated in many ecosystems under a wide range of environmental conditions. However, there is no information on how fire affects faunal biodiversity in deciduous forest ecosystems prone to winter fires, such as those on the southern slopes of the Alps. The main aim of this study was to analyse the effects of single and repeated fires on the structure and species diversity of spider communities in chestnut forests in southern Switzerland. A second objective was to interpret the ecological response of forest‐floor habitats to wildfires, using epigeic spiders as bioindicators. One‐hundred and thirty‐three spider species were found in pitfall trap samples collected between April and September in burnt and control sites in chestnut coppices. Species richness and community composition were influenced by fire frequency and the time elapsed since the last fire. About 19% of the species were trapped exclusively in sites that had been repeatedly burnt, while 11% occurred only in unburnt coppice. Post‐fire development of the spider community was chiefly from individuals that survived in situ. We found no characteristic pioneer species in any of the burnt sites. There were indirect effects of fire on the spider community, through interactions between species arising from the changing environmental conditions following a fire. After a single fire, changes in community composition were only observable during the first 2 years. At sites that had experienced repeated fires, there was a more persistent influence on community composition. These sites were characterized by an increase in species richness and species diversity. The presence of a wide ecological range of species in ‘repeated fire’ sites was probably due to the mosaic structure of the environment and the wide range of microclimate conditions at the soil surface, with a predominance of xeric conditions. The spider communities of chestnut forests were resilient to disturbance by fire. Both the formerly intensive management of these forests (until the 1950s) and a history of frequent fires that goes back to the Neolithic period have played an important part in the development of the spider community in these forests.

Closed mark-recapture models to estimate species richness: An example using data on epigeal spiders

Species richness is a fundamental ecological property. The problem of estimating the number of species is quite similar to that of estimating the population size of a single species. Some authors of mark-recapture statistics have proposed using some of these methods to estimate species richness. This necessitates understanding how the recording probabilities of individuals differ from those of species. In particular, the species of a species pool are likely to exhibit a wide range of recording probabilities. Depending on sampling conditions, temporal or spatial variation in species detection probability may also occur, making model M th estimators particularly useful. Empirical detection probabilities and estimates of species numbers using three coverage, one point, and two jackknife estimators are presented for series of spatial and temporal trapping occasions of epigeal spiders.

The effects of varied grazing management on epigeal spiders, harvestmen and pseudoscorpions of Nardus stricta grassland in upland Scotland

A hypothesis that epigeal arachnid assemblages benefit more from greater vegetation structure than botanical species composition in upland grasslands was tested. The test was carried out within a grazing experiment, initiated in 1991, to investigate vegetation dynamics in response to stocking with mixed livestock at varied rates. The experimental treatments comprised: no livestock, sheep only or sheep with cattle. Livestock treatments were grazed to maintain either 4.5 or 6.5 cm average sward heights between tussocks. Two replicates of each treatment were used and allocated to 10 plots across 22 ha of Nardus stricta-dominated grassland. The effects on epigeal arachnids (excluding acarines) of the botanical and structural differences of the grassland between treatments during April–October 1993 and 1994 were assessed. Epigeal arachnid species composition was estimated using continuous pitfall trapping and the densities of mainly money spiders (Araneae: Linyphiidae) were estimated from monthly suction sampling and visual counts of spider webs in micro-habitats. These data were later compared with stocking rate, botanical species composition and vegetation structure. Forty of the 84 sampled species occurred in all experimental treatments. There was a significant effect of treatment on the number of arachnid species in suction but not in pitfall samples. There was also a significant effect of treatment on the relative abundance of 26% of these arachnid species. For most species of spider, harvestmen and pseudoscorpion, abundance was greater in the ungrazed and taller, grazed swards although a few species were captured in greater numbers in the treatments with shorter swards. Botanical composition, mean vegetation height and grazing intensity accounted for 48.5–53.2% of the variability in the species composition/relative abundance of these arachnids, calculated by direct gradient analysis. Almost half of the species were randomly distributed across the experimental treatments and are recorded as widespread in upland heathland or grassland habitats and lowland grassland. More spider webs were counted during July–September 1993–1994, with greater numbers (dominated by the linyphiid species, Lepthyphantes mengii) counted in tall, ungrazed swards compared with taller grazed swards created by sheep alone or sheep with cattle. In the treatments with fewer webs, these were occupied by more linyphiid species. Suction sampling detected greater diversity of arachnids in the ungrazed N. stricta. This was related to increased plant litter below the leaf stratum where webs were counted. Vegetation structure and not botanical species composition within the N. stricta plant community determined arachnid species composition and abundance. Furthermore, no single grazing treatment supported the total number of arachnid species represented across the entire grazing experiment. It is concluded that varied grazing management, including some temporary ungrazed areas, is necessary to maintain the structural variability of grassland patches so as to maintain a spatial mosaic that favours the optimum arachnid fauna of upland grasslands.

Evaluation of population densities of the common wolf spider Pardosa agrestis (Araneae: Lycosidae) in Hungarian alfalfa fields using mark-recapture

The absolute population density of adult Pardosa agrestis (Westring, 1862), the dominant epigeic spider species in many arable lands in Central Europe, was quantified in two alfalfa fields using a multiple mark-recapture method. The resulting density estimates are presented together with catch data from simultaneously performed suction sampling and pitfall trapping. Two week long mark-recapture surveys were conducted in August 1995 and 1996 using grids of 11 × 11 live-catching pitfall traps covering a square area of 400 m2 in the first, and 900 m2 in the second survey. The trap checking and marking procedure, using individual codes, was done daily. Over 5,000 spiders were marked in the two surveys. The number of spiders caught varied greatly between days. The recapture rate was also variable, ranging between 5-19%. Recaptured animals moved considerable daily distances, marked animals left the area of the trapping grid within a few days. Population sizes were estimated for 3 day time windows during which period the population could be considered closed. Spider densities were calculated from the estimated abundances and the capture area, which consisted of the grid area plus a boundary strip calculated from the estimated movement ranges of spiders. The resulting densities were close to 2 males and 1 female per m2 in the first, and 4.5 males and 4.5 females per m2 in the second experimental site. Suction sampling caught very few adult individuals and gave unsatisfactory data for statistical comparison. Live catching pitfall trap catches did not correlate with the derived mark-recapture density estimates across the short time windows, but for the entire trapping sessions the catches were consistent with the density estimates.

Epigeic spiders of the pastures of northern Wielkopolska

Epigeic spiders of the pastures of northern Wielkopolska

A TWENTY-YEAR COMPARISON OF EPIGEIC SPIDER COMMUNITIES (ARANEAE) OF DANISH COASTAL HEATH HABITATS

Abstract The same epigeic spider communities of North-west Jutland coastal heath habitats (Denmark, region Thy) initially surveyed by pitfall traps from 1977–79 were examined 20 years later (1997–98). The heath plots were open sandy areas growing into Calluna heath, and the more stable Erica, Calluna/Empetrum, Molinia vegetation types. They have changed vegetatively only a little in those 20 years from natural succession. Though the spider communities of all areas showed only minor changes from the passage of time, these were larger than the differences attributable to the different habitat types despite large differences in soil humidity and vegetation structure.

Side‐effect of integrated pest management and conventional spraying on the composition of epigeic spiders and harvestmen in an apple orchard (Araneae, Opiliones)

The effect of two different integrated pest management (IPM) practices and conventional spraying (CHEM) on the composition of epigeic spiders and harvestmen in an apple orchard was investigated over 4 years. Conventional spraying included more frequent and nonselective pesticide applications, whilst IPM plots were treated with selective pesticides and less frequently. One of the IPM plots was undersown with various plantings, the other with grass, and the plot under conventional spraying was covered with weeds. In total, eight species of harvestmen and 65 species of spiders were recorded whose abundance peaked in spring and autumn. Arachnids were on average over the 4 years less abundant on both IPM plots than on CHEM which seems to be due to lower plant density of weed cover. Seasonal oscillations were only slightly different in particular seasons between plots, in particular during spraying. In 1992 the arachnids were a little more abundant on the conventional spraying plot, in 1993 on IPM plots and during subsequent 2 years the difference diminished. The seasonal abundance appeared to be influenced by herbicide applications. Species diversity of all plots were higher than in crop fields, but did not reveal disagreement between plots. The numerical hierarchical classification (TWINSPAN) detected that the composition of arachnids was influenced in particular by annual variation. The arachnid assemblages of the studied plots were not found to be markedly different during the whole study. The effect of IPM practices and conventional spraying on the composition of epigeic arachnids was far less apparent than it was in arboreal species. However, nearly 20% of spiders were found common with crown stratum. Some of them occupied both strata, a few occurred in epigeon only accidently, while others moved vertically during the season. Thus the epigeic fauna seems to support arboreal spiders.

Effect of pest management systems on ground-dwelling spider assemblages in an apple orchard in Hungary

Ground-dwelling spider assemblages in differently treated plots of a Hungarian apple orchard were investigated by pitfall trapping. The samples were taken weekly from April to November over three years as part of a study to compare the effects of integrated pest management based on selective insecticides, with conventional control utilising broad-spectrum compounds. Attention was also paid to the effects of boundaries and of different weed patterns on the spider assemblages. No significant differences were found between the conventional and IPM plots in species richness and composition, density and diversity of epigeic spider communities. The density in the IPM plots was moderately higher in only one year. Greater spider densities were observed in the tree rows where the weed coverage was higher than in the alleys where mechanical weed control was applied. However, community structures did not differ significantly. Near the edge of the orchard, the density and species richness of epigeic spiders were higher and the community structure differed slightly from that of the orchard habitats. The spiders showed one population peak in springtime in all habitats, but this was more extended in the edge. The collections included 1147 individuals representing 37 species, with Xysticus kochi, Pardosa agrestis and Titanoeca schineri being the most dominant species. Their population dynamics, sex ratio and habitat preferences are also discussed.

The Impact of Different Agricultural Land-uses on Epigeal Spider Diversity in Scotland

Detailed knowledge of the biodiversity of spider communities on agricultural land is important both in terms of enhancing pest control and understanding the driving forces influencing nature conservation value. Pitfall traps were used to assess spider species diversity at 71 Scottish agricultural sites between May and September during 1996 and 1997. Land-use varied from intensive arable fields, grasslands and extensive heather (Calluna vulgaris) moorland. Spider species richness (S) was found to decrease significantly as farm management intensity increased. Several linear regression models based on the 1996 data (50 sites) and a selection of plant, soil and landscape variables explained up to 88% of the variation in species richness. Four of these models were used to estimate 1997 species richness (36 sites: 15 repeat and 21 new) and up to 58% of sites were correctly predicted to within ± four species of the actual number caught. As only 60% of the repeat 1997 sites had values of S within four units of their 1996 score, this suggested a relatively high level of model accuracy. Model accuracy increased to 64% when all four models were used for each site, suggesting the individual models should be targeted at specific land-use types. We discuss the relevance of these models for predicting the consequences of changes in agricultural land-use for spider diversity.

The epigeic spider fauna (Arachnida: Araneae) of some fens in north-eastern Iceland - a comparison of areas differing in ground moisture and vegetation

The investigation dealt with the epigeic spider fauna of a fen area in north-eastern Iceland. The mires in question consisted of a mosaic of subparts differing in ground moisture and vegetation. The aim of the study was to determine whether the spider communities differed correspondingly. Pitfall trapping, vegetation mapping and ground moisture estimation were carried out at 11 different sites. 7958 adult spider individuals belonging to 41 species collected. The study sites varied more in abundance of the spiders than in species composition. Grouping of spider species according to their main occurrences along the two gradients of ground moisture and shrub cover is decribed.

Changes in epigeic spider community in primary succession on a brown-coal dump

Changes in epigeic spider community in primary succession on a brown­ coal dump. A descriptive model of primary succession of spiders on a brown-coal dump is presented. Multivariate methods (cluster analysis and detrended correspondence analysis), and community indexes were applied to evaluate changes in community composition of epigeic spiders. Two different rehabilitation age stages were investigated. The cluster analysis helped to determine a case of horizontal asynchronous succession. The DCA was able to distinguish divergent trends of succession from the initial stage. Successional trends in species replacements were observed. In all aspects of succession there was found to be directional towards a ruderal steppe subclimax.

Water balance, respiration and immobilisation in relation to deltamethrin poisoning and physical conditions in the epigeal spider Oedothorax apicatus

AbstractThe effect of a pyrethroid insecticide, deltamethrin, on water loss, metabolic rate and immobilisation was studied, using the epigeal spider Oedothorax apicatus (Blackwall) (Linyphiidae) as a test species. Water loss was measured gravimetrically at different temperatures, air humidities, and doses of deltamethrin. Metabolic rate and immobilisation were measured at different temperatures and doses. Immobilisation was measured at different relative humidities and temperatures. Water loss due to evaporation increased linearly with vapour pressure deficit. The slope of the latter relationship increased with temperature, indicating an increase in cuticle permeability with temperature. In addition to water loss by evaporation, deltamethrin treatment induced water excretion. This was positively related to dose and temperature, but independent of air humidity. Metabolic rate increased with temperature and dose. Immobilisation was highest at low temperatures in combination with low air humidity. The consequences of pesticide‐induced water excretion are discussed with respect to field‐ and laboratory‐based dose‐effect relationships for pyrethroids presented in the literature. The present results seem to offer an explanation for hitherto unexplained minima in temperature‐response curves in pyrethroid toxicity in some arthropod species. It is concluded that simultaneous measurements of metabolic rate, water‐loss rate and pesticide effects are a prerequisite for an understanding of the effects of pesticides on arthropods.

Epigeic spiders, their potential prey and competitors: Relationship between size and frequency.

In an analysis of 67 pitfall trap studies in different environments a positive correlation is found between the abundance of spiders and their potential prey, individual main prey groups and individual predator groups. The body-size of spiders and potential prey is significantly correlated both during the day in one locality and between five different localities. Spiders match the size spectrum of their potential prey by an almost equally broad spectrum, whilst the size spectrum of other predator groups is narrower. Therefore, in all size classes spiders exercise optimal predator pressure upon their potential prey. It is suggested that there may be a significant role for spiders as a multi-predator complex in reducing a multi-prey complex.