On the Relationships between Ground-dwelling Spider (Araneae) Assemblages and Dead Wood in a Northern Sugar Maple Forest

Downed woody material (fallen logs) offers ground-dwelling spiders (Araneae) ideal sites for nesting and foraging, but little is known about what characteristics of dead wood influence spider assemblages. In a maple forest of Forillon National Park, in eastern Québec (Canada), spider assemblages on, adjacent to, and away from fallen logs were compared. We also tested how log type (coniferous vs. deciduous) and decomposition stage influenced spider assemblages. Sampling was done for an intensive four-week period using both litter samples and pitfall traps. A total of 5613 spiders representing 83 species from 16 families was collected. Spiders were affected by the presence of logs, as both species diversity and total number of individuals collected were significantly higher on the log surface compared to the forest floor. Ordination analysis revealed a distinct compositional difference between the spider fauna found on the wood surface compared to the forest floor. Wood type and decomposition stage had few significant effects on spider assemblages, except that less decayed logs supported higher spider diversity than logs in advanced stages of decay. Dead wood is clearly important for generalist predators such as spiders, further supporting the conservation importance of fallen logs in northern forest ecosystems.     

Communities of ground-living spiders in deciduous forests: Does tree species diversity matter?

The relationships between species diversity and ecosystem functions are in the focus of recent ecological research. However, until now the influence of species diversity on ecosystem processes such as decomposition or mineral cycling is not well understood. In deciduous forests, spiders are an integral part of the forest floor food web. In the present study, patterns of spider diversity and community structure are related to diversity of deciduous forest stands in the Hainich National Park (Thuringia). In 2005, pitfall trapping and quantitative forest floor sampling were conducted in nine plots of forest stands with one (Diversity Level 1), three (DL 2) and five (DL 3) major deciduous tree species. Species richness, measured with both methods, as well as spider abundance in forest floor samples were highest in stands with medium diversity (DL 2) and lowest in pure beech stands (DL 1). The Shannon-Wiener index and spider numbers in pitfall traps decreased from DL 1 to DL 3, while the Shannon-Wiener index in forest floor samples increased in the opposite direction. Spider community composition differed more strongly between single plots than between diversity levels. Altogether, no general relationship between increasing tree species diversity and patterns of diversity and abundance in spider communities was found. It appears that there is a strong influence of single tree species dominating a forest stand and modifying structural habitat characteristics such as litter depth and herb cover which are important for ground-living spiders.     

Contrasting responses of web-building spiders to deer browsing among habitats and feeding guilds

We examined web-building spider species richness and abundance in forests across a deer density gradient to determine the effects of sika deer browsing on spiders among habitats and feeding guilds. Deer decreased the abundance of web-building spiders in understory vegetation but increased their abundance in the litter layer. Deer seemed to affect web-building spiders in the understory vegetation by reducing the number of sites for webs because vegetation complexity was positively correlated with spider density and negatively correlated with deer density. In contrast, the presence of vegetation just above the litter layer decreased the spider density, and deer exerted a negative effect on this vegetation, possibly resulting in an indirect positive effect on spider density. The vegetation just above the litter layer may be unsuitable as a scaffold for building webs if it is too flexible to serve as a reliable web support, and may even hinder spiders from building webs on litter. Alternatively, the negative effect of this vegetation on spiders in the litter may be as a result of reduced local prey availability under the leaves because of the reduced accessibility of aerial insects. The response to deer browsing on web-building spiders that inhabit the understory vegetation varied with feeding guild. Deer tended to affect web-invading spiders, which inhabit the webs of other spiders and steal prey, more heavily than other web-building spiders, probably because of the accumulated effects of habitat fragmentation through the trophic levels. Thus, the treatment of a particular higher-order taxon as a homogeneous group could result in misleading conclusions about the effects of mammalian herbivores.     

Effects of agricultural practices and fine-scale landscape factors on spiders and a pest insect in Japanese rice paddy ecosystems

We examined the effects of environmentally friendly (EF) farming and landscape factors on the abundances of major spider guilds and a rice pest, the small brown planthopper (SBPH), Laodelphax striatellus (Fallén), in a Japanese rice paddy ecosystem. The abundances of all spider guilds increased by EF farming, whereas different spider guilds showed contrasting responses to the size of the forest within 200 m of the fields. The abundances of ground spiders and horizontal web weavers increased with increasing forest area, unlike small ground spiders, whose abundance decreased. The abundances of SBPH nymphs and adults decreased by EF farming but responded differently to landscape: nymphs decreased with increasing forest area, but adults did not. Further analysis indicated a potential negative relationship between web-weaving spiders and SBPH nymphs. Our findings suggest that the size of the forest adjacent to fields is an important determinant of spider guild composition and pest abundance.     

The effects of habitat parameters and forest age on the ground dwelling spiders of lowland poplar forests (Hungary)

Forest management has highly modified the structure of the European forests. Harvesting and post-harvest regeneration leads to a simplified forest structure. Our main objective was to detect the effects of habitat structure and forest age on the ground-dwelling spider diversity and assemblage composition of poplar forests at the Hungarian Great Plain. Our results demonstrate that the rarefaction diversity and the number of forest specialists closely correlated with the structural parameters of the forest floor, however, the age and canopy closure did not influence these parameters. According to redundancy analysis, the composition of spider assemblages was determined solely by habitat structure, with habitat structure having a major effect on the species composition and diversity of spider assemblages. A direct effect of forest age on the spider assemblages was not detected, due to the presence of different habitat types in the surrounding landscape, which may serve as suitable habitats for source-populations of spiders with different habitat requirements. Our results highlight the importance structural complexity of forests for maintaining forest spider diversity and preserving the regional species pool of spiders.     

Effect of an invasive ground cover plant on the abundance and diversity of a forest floor spider assemblage

Ground dwelling spiders are important predators in the detrital food web, which plays important roles in nutrient cycling and energy flow in forest ecosystems. The cursorial spider assemblage in a Beech-Maple forest in southwestern Michigan at sites where and invasive plant, Vinca minor, has invaded was compared to a native site within the same forest and to the forest prior to invasion by the plant. Pitfall traps were used to sample cursorial spiders over the course of a summer. Vinca minor substantially altered the forest floor spider assemblage. The invasive plant reduced the total activity-abundance of spiders by nearly 49% and depressed species diversity and evenness; in contrast, species richness was not affected. We found that V. minor changed the guild and family structure with wolf spiders being common at sites where the plant had invaded. Vinca minor reduced the abundance of vagrant web building and crab spiders. Similarity indices revealed that the spider communities between the two sites were quite dissimilar (Bray-Curtis = 0.506; Jaccard’s = 0.520). Importantly, comparison to a study conducted in the same forest 28 years earlier showed that the cursorial spider assemblage in the forest prior to Vinca invasion was very different than it was after Vinca invaded but was similar to the current native site in species and guild composition. We conclude that invasion by Vinca has caused the striking changes we observed in community organization of this important group of forest floor predators. We suggest that changes in the physical structure of the litter/soil microhabitat with the invasion of V. minor are likely the cause of the substantial impacts of the plant on the spider assemblage.     

Spiders and Other Arthropods as Indicators in Old-Growth Versus Logged Redwood Stands

This study, conducted in the Santa Cruz Mountains of California, provides data on the abundance and diversity of litter spiders and other arthropods in three redwood forest conditions: old growth, second growth, and tree farm. Litter spiders are linked to and reflect habitat structure and prey abundance and can act as indicators for redwood forest restoration and monitoring. There were significant declines in spider and other arthropod diversity and abundance with increased logging and decreased herb cover. The absolute and relative increase in nocturnal spiders and detritivores in unlogged sites suggests that guild structures of spiders and other arthropods can indicate forest recovery from logging disturbance. Furthermore, selectively harvested stands do not retain old‐growth levels of litter arthropod diversity or abundance. This study identifies potential indicator redwood litter spiders that show higher abundances in old‐growth areas, Zelotes sp. (Gnaphosidae), Xysticus sp. (Thomisidae), and Ceratinops inflata (Linyphiidae) and a possible old‐growth specialist, Phrurotimpus sp. (Liocranidae). These findings strengthen the case for including soil arthropods in redwood forest monitoring and assessment and for the preservation of undisturbed forest areas.     

Spiders (Araneae) associated with downed woody material in a deciduous forest in central Alberta, Canada

1 Spiders (Araneae) were collected on and near downed woody material (DWM) in a Populus‐dominated forest to determine if spiders utilize wood surfaces, and to ascertain the importance of DWM habitat and wood elevation for spider assemblages. 2 Over 10 000 spiders representing 100 species were collected. Although more spiders were collected on the forest floor, spider diversity was higher in traps located on wood surfaces than on the forest floor, and 11 species were collected more frequently on wood surfaces. 3 Spiders utilized DWM at different stages in their development. Female Pardosa mackenziana (Keyserling) (Lycosidae) carrying egg sacs were caught most often on the surface of DWM, possibly to sun their egg sacs. Additionally, the proportion of immature spiders was higher on the wood surface than on the forest floor. 4 Spiders collected on logs with and without bark were compared to assemblages collected on telephone poles to assess what features of DWM habitat may be important. Web‐building species were seldom collected on telephone poles, suggesting that they depend on the greater habitat complexity provided by DWM. In contrast, hunting spiders did not distinguish between telephone poles and logs. 5 Fewer spiders and a less diverse fauna utilized elevated compared to ground‐level wood. Additionally, Detrended Correspondence Analysis revealed that the spider community from elevated wood was distinguishable from the spider community from ground‐level wood, and from the forest floor spider community.     

The influence of variation in litter habitats on spider communities

Summary Spider communities were sampled over an artificial gradient of litter depth (created by raking) and compared to those of two other forests exhibiting natural variation in litter depth. More species of spiders were present in areas of greater depth and/or complexity in all sites. Relative abundance of Lycosidae decreased, while relative abundance of Clubionidae, Thomisidae and Gnaphosidae increased over gradients of increasing depth and complexity. Similarity of species composition between areas within a forest was related to site differences in litter depth and structure.As litter depth increased, there were significant changes in prey species richness, litter complexity, and microclimate. Partial correlation analysis of grouped data from early-, mid-, and late season suggests that influential factors change with season. In the early season, prey abundance and temperature variation account for most of the variation in spider species richness. In mid-season, litter complexity and moisture fluctuations appear to influence richness, with complexity relatively more important. In late season, complexity and temperature range were the primary factors, with temperature relatively more influential. The relative importance of these factors in influencing community structure of spiders is discussed.     

Importance of habitat structure to the arthropod food-web in Douglas-fir canopies

This study tested the hypothesis that habitat structure dictates the distribution and community composition of arboreal arthropods. A diverse arthropod assemblage of Douglas-fir canopies, which included Araneae, Psocoptera, Collembola and Homoptera, was chosen as a model system. Habitat structural diversity, defined as needle density and branching complexity of Douglas-fir branches, was manipulated in a four-month experiment by needle removal, thinning and tying of branches. Abundance of canopy spiders declined significantly following needle density reduction and branch thinning, branch tying significantly increased spider abundance. Distinct habitat utilization patterns were found among individual spider guilds. Orb weavers (Araneidae) dominated spider assemblages in structurally simple habitats, whereas tied branches were colonized primarily by sheet-web weavers (Linyphiidae) and nocturnal hunting spiders (Anyphaenidae and Clubionidae). Spider species richness and average body size of several spider species increased in structurally more complex habitats. Arboreal spiders appeared to be limited by strong bottom-up effects in the form of habitat quality and, to a lesser degree, prey availability. Habitat manipulations did not affect densities or biomass of flying arthropod colonists in the branch vicinity. Needle removal and branch thinning led to a significant decline in the abundance of Psocoptera and Collembola. Tying of branches resulted in an eight-fold increase in Collembola numbers, organisms most sensitive to habitat alterations. Canopy habitat structure modified vertical dispersal of Collembola from forest litter, which may have significant implications for arboreal consumers. Our results lend strong support to the importance of habitat structural diversity in explaining general patterns of arthropod abundance and diversity on plants.     

海南天然林与橡胶林蜘蛛多样性比较

为探索天然林和橡胶林蜘蛛多样性现状,于2010年8月在海南黎母山自然保护区选取天然林和橡胶林,采用扫网法、陷阱法和单位面积法收集蜘蛛标本,分析两种林型之间蜘蛛组成、多样性和功能群差异,并以蜘蛛科和数量分布为属性进行主成分分析(PCA),探讨林型中样方之间蜘蛛群落的相似性。共采集蜘蛛标本3609头,用于统计分析的成蛛969头,归属于23科,162种。天然林20科,100种,优势类群为跳蛛科、球蛛科和园蛛科;橡胶林17科,87种,优势类群为肖蛸蛛科、狼蛛科和猫蛛科。从蜘蛛的数量分布看,橡胶林蜘蛛个体密度显著高于天然林;而天然林多样性指数和丰富度指数显著高于橡胶林。橡胶林中结圆网型和游猎型蜘蛛显著高于天然林,结皿网型显著低于天然林,伏击型不存在显著性差异。PCA分析结果表明,24个样方趋于分成天然林和橡胶林2组,并且天然林样方之间相似性极高,而橡胶林样方之间相似性相对较低。以上结果表明:(1)橡胶林替代天然林后蜘蛛群落结构发生变化,多样性降低;(2)增加生境结构的复杂性和减少人为干扰对保护和恢复物种多样性有重要意义。     

Refuge from cannibalism in complex-structured habitats: implications for the accumulation of invertebrate predators

Abstract.  1. Like many invertebrate predators, the wolf spider Pardosa littoralis Banks (Araneae: Lycosidae) accumulates in complex-structured habitats replete with leaf litter (thatch). Here we test the hypothesis that P. littoralis accumulates in complex habitats to gain refuge from cannibalism.
2. A laboratory experiment examined the effects of habitat complexity (thatch present or absent) and size-class pairing of conspecific spiders (large vs. small, small vs. small, and large vs. large) on the incidence of cannibalism. Spider survival was significantly higher (22%) in complex-structured habitats with thatch than in simple-structured habitats lacking thatch. Furthermore, cannibalism occurred more frequently in P. littoralis when the size of conspecifics was asymmetric (large vs. small spiders) than when spiders were of equal size. There was no interactive effect of habitat complexity and size-class pairing on spider survival.
3. A field experiment examined the effects of habitat complexity, conspecific density, and access to alternative prey on the prevalence of cannibalism in P. littoralis . Access to alternative prey significantly increased the number of spiders recovered from field enclosures, as did the presence of leaf litter thatch. That fewer spiders were recovered when thatch and alternative prey were absent suggests that cannibalism was most prevalent under these conditions.
4. Overall, results suggest that habitat complexity reduces agonistic interactions and cannibalism among wolf spiders, providing encouragement to pest managers that the structure of agricultural habitats can be managed to maximise densities of generalist predators for enhanced pest suppression.     

A functional relationship between species richness of spiders and lichens in spruce

Modern forestry has created stands with even age distribution of trees and fragmentation of the habitat. In boreal forests, the effects on biodiversity within many taxa need to be examined. We tested the hypothesis that species richness of foliose and fruticose lichens and spiders is positively related in the lower canopy of spruce (Picea abies) in forests with, or without, management in central Sweden. High species richness of lichens may increase the structural complexity of the microhabitat on spruce branches, and bring a higher species richness also in the spider community. In six areas, spruce branches were sampled in old-growth and managed boreal forest stands, respectively. Forest management did not affect the species richness of spiders or lichens, but an effect due to sampling area was found in the latter taxon. There was a significant covariation between species richness of lichens and spiders, and the hypothesised positive correlation was confirmed by separate analyses for each area and combining the probabilities. Moreover, regression analysis on mean values from each site revealed a positive relationship. We conclude that species richness of lichens and spiders covary on spruce branches for functional reasons, i.e. more lichen species promotes a more diverse spider community by increasing the structural heterogeneity. Our results might provide a shortcut for assessing biodiversity in boreal forests.     

The effect of a single colony of the red wood ant,Formica polyctena,on the spider fauna (Araneae) of a beech forest floor

Summary The predation on spiders in a forest ecosystem by a colony of red wood ants, Formica polyctena, was estimated using a barrier to isolate the colony. Of the ants' total prey, 4.6% were spiders. In order to estimate the effect of F. polyctena within their hunting area on the spider population, the spiders' population density was studied inside and outside the hunting area. Samples of the forest floor were taken, spider webs were counted and pitfall traps were used. No significant difference was found in density or composition of the spider fauna inside and outside the hunting area.     

Tree Species Richness Strengthens Relationships between Ants and the Functional Composition of Spider Assemblages in a Highly Diverse Forest

In species‐rich ecosystems, such as subtropical and tropical forests, higher trophic level interactions are key mediators of ecosystem functioning. Plant species loss may alter these interactions, but the effects of plant diversity might be modified by intraguild interactions, particularly among predators. We analyzed the relationships between spiders and ants, two dominant predatory arthropod taxa, on tree saplings across a gradient from medium to high woody plant species richness in a subtropical forest in Southeast China. Neither ant nor spider total biomass was significantly related to plant species richness. By contrast, the biomass distribution of web‐building and hunting spiders changed and spider family richness increased in the presence of ants, resulting in more web builder‐dominated assemblages. However, these relationships depended on the plant communities, and were stronger in plots with higher plant species richness. Our results indicate that in addition to potential effects of ants on hunting spiders in particular, ants could indirectly influence intraguild interactions within spider assemblages. The observed shifts in the spider assemblages with increasing ant presence and plant species richness may have functional consequences, as web‐building and hunting spiders have distinct prey spectra. The relationships among ants, spiders, and plant species richness might contribute to explaining the non‐significant relationship between the overall effects of predators and plant diversity previously observed in the same forest plots. Our findings thus give insight into the complexity of biotic interactions in such species‐rich ecosystems.     

The impact of altered precipitation on spatial stratification and activity-densities of springtails (Collembola) and spiders (Araneae)

Abstract.  1. A field experiment was conducted to determine how short-term changes in moisture can alter activity-densities of spiders and springtails.
2. In a Kentucky forest 10 unfenced 4-m² plots were divided into two rainfall treatments. A clear roof over five plots excluded rainfall to simulate severe drought conditions ( drought treatment). Water was sprayed on the five uncovered plots at a rate equal to two times the long-term mean in order to establish the high-rainfall treatment. Activity-densities of Collembola and spiders were measured using pitfall traps designed to sample the top, middle, and bottom layers of leaf litter. The experiment ran from 20 July to 23 September 2001.
3. Overall (i.e. litter layers pooled) activity-density (mean number trapped each sampling date) of Collembola was ≈ 60% lower in drought plots than in plots receiving increased precipitation. Surprisingly, overall spider activity-density was ≈ 1.6 times greater in the drought plots.
4. Differences in rainfall affected the spatial stratification of Collembola and spiders in strikingly different ways. Activity-densities of neither group differed between drought and high-rainfall treatments in the bottom litter layer. Collembola activity-density was three times greater in the top and middle litter layers in high-rainfall plots than in drought plots. In contrast, spider activity-density did not differ between treatments in the top layer, but activity-density was decreased by 50% in the middle layer of high-rainfall plots compared with drought plots.
5. Three Collembola families (Sminthuridae, Tomoceridae, and Entomobryidae) accounted for most of the Collembola pattern. The spider response was due to altered activity-density of one family of wandering spider, the Gnaphosidae.     

Spider diversity responds strongly to edge effects but weakly to vegetation structure in riparian forests of Southern Brazil

Riparian forests bordering open terrestrial environments may have three microhabitats differing in structure and conditions: a grassland/pasture-forest edge (GE), a forest interior (FI) and a river–forest edge. The influence of such edge effects and vegetation characteristics on spider diversity of riparian forests was evaluated in Southern Brazil. Four different rivers were sampled on the tree–shrub strata with a beating tray, twice per season for 2 years. There were six transects per river, two per microhabitat. We compared spider abundance, species richness and composition. Vegetation variables sampled were vertical structure and (horizontal) density, canopy height and cover. Overall 42,057 spiders were sampled, 28 spider families and 440 species. The FI had higher spider abundance than the edges. Average species richness differed among rivers. Microhabitats did not differ in average richness, although overall richness (from sample-based rarefaction) was higher for GE than FI. High abundances in FI may result from lowered stress due to abiotic conditions, while higher GE richness may result from a faunal superposition between forest species and those from the grassland/pasture. Only canopy cover returns a positive relationship with spider diversity (richness and adult abundance). This might result from more spider species preferring to build webs or hunt under low-light environments. Rivers had spider faunas differing in composition but among microhabitats species composition was the same. Vegetation structure has been hypothesized to affect spiders, but this impact might be best seen in specific subgroups or guilds within spiders, not in the whole assemblage.     

Understory spider assemblages from a cloud forest in Chiapas,Mexico, and their relationships to environmental variables

Cloud forests have high ecological complexity, but their reduced area and exploitation by human communities, make them one of the most endangered ecosystems in Mexico. The spider assemblages of a cloud forest reserve in Chiapas, Mexico, were studied to analyze influence of environmental variables (forest stand structure, temperature and relative humidity) and their temporal variation, on the distribution, abundance, species richness and assemblage structure of spiders. Ten parcels were established for the sampling of spiders and the recording of forest and climatic variables. Spider sampling took place during the dry and rainy seasons. Vegetation data were recorded at the end of the study (except canopy cover, which was registered at the end of each season). Some differences were found among parcels in forest stand structure, but only the density of seedlings showed a high correlation with spider abundance, seemingly seedlings (by its size and architecture) offered numerous supports for the understory spiders’ webs and then promote the settlement of weaver spiders. Also there were some correspondences between the similarity patterns of forest structure and spider assemblages, giving some evidence of a forest structure influence on the integration of spiders’ assemblages. Spider abundance was notoriously higher in the dry season. Other environmental variables had only weak effects on spider variables (abundance and species richness) and assemblage structure. The most abundant families were Tetragnathidae, Theridiidae and Linyphiidae, which were also among the dominant families in other tropical cloud forests, with the latter two also being among the most diverse. As complex ecosystems, tropical cloud forests seem to have complicated interactions with their inhabitant animals, not easy to elucidate.     

Dynamics of aquatic insect flux affects distribution of riparian web-building spiders

The flux of emerging aquatic insects from streams can provide a significant energy subsidy to riparian web-building spiders. However, despite the high temporality of aquatic insect emergence, the effects of such aquatic insect dynamics on spider distribution are poorly understood. To examine the relationship, the aquatic insect flux from a headwater stream in a northern Japanese deciduous forest was experimentally manipulated by using a greenhouse-type covering, during May to July. Under natural conditions, the aquatic and terrestrial insect abundances dramatically decreased and increased from May through July, respectively. The experimental reduction of aquatic insect flux depressed the density of horizontal orb weavers (Tetragnathidae) in both May and June, but not in July when aquatic insects were scarce, indicating a temporal limitation on spider distribution by aquatic insect flux. In contrast, the densities of both vertical orb weavers (Araneidae) and sheet weavers (Linyphiidae) were unaffected by the manipulation throughout the study period. These various responses, differing among months or spider guilds, may be attributed to the degree of specialization for aquatic prey in the spiders and their mobility in response to aquatic insect flux. The experimental results provided direct evidence that the temporal dynamics of aquatic insect flux, as well as spider characteristics, were primary factors determining the distributional patterns of riparian web-building spiders.     

Influence of fine woody debris on spider diversity and community structure in forest leaf litter

Exploitation of forests for biofuel results in variable amounts of fine woody debris (FWD) being left on the forest floor. Such practices have the potential to affect the diversity and taxonomic composition of litter-dwelling organisms. The ability to predict the consequences of harvesting biofuel will be strengthened by knowledge of how variation in FWD affects litter organisms in non-harvested forests. A field experiment with three treatments [Control (no manipulation), FWD Removal, and FWD Addition] was carried out in replicated open plots in an unexploited forest in order to determine how the amount of fallen FWD affects the abundance, diversity and community composition of spiders, selected because of their importance as predators in the leaf-litter food web. Manipulation of FWD started in August, and by the following July total spider density in the FWD Addition treatment was 1.6× that of FWD Removal plots. Spider density in FWD Removal plots was 30% lower than the Control treatment, with no statistically significant difference between Control and FWD Addition. Manipulating FWD had no statistically significant effects on standard indices of spider diversity. However, multivariate community-level analyses revealed statistically significant differences in spider community structure between the FWD Removal and FWD Addition treatments. Two dominant genera of web builders contributed the most to this effect of manipulating FWD. Our results, and the findings of studies of woody debris in younger forests, suggest that the relatively small effects of FWD in our field experiment may reflect the age of the forest, with effects on the fauna likely being larger in forests younger than the one we studied.