Spider Community Composition Research Articles

Dwarf shrubs may mitigate the negative effects of climate change on spiders by moderating microclimate

Climate change negatively affects arthropod biodiversity worldwide. Mitigating the resulting arthropod decline is a great challenge. Dwarf shrubs in open areas might buffer microclimatic extremities by reducing the solar radiation reaching the ground and weakening air circulation near the soil surface. Forest steppes are mosaics of forests and grasslands covering a vast area in Eurasia. This heterogeneous ecosystem offers the opportunity to study the effect of small habitat features, i.e. dwarf shrubs, in dry grasslands and compare the fauna of rosemary-leaved willow (Salix rosmarinifolia) shrubs with forest patch interiors, open grasslands and their edges. We hypothesized that the dwarf shrub microhabitat has a wetter and cooler microclimate than open grassland and a different spider community composition than other forest-steppe microhabitats. We recorded microclimatic parameters with data loggers, measured soil moisture with TDR and collected ground-dwelling spiders with pitfall traps. We detected the highest soil moisture (6.26 ± 1.21%, mean ± 95% confidence interval) and air humidity (80.19 ± 3.19%) in forests and the lowest in grasslands (4.36 ± 0.65%; 66.59 ± 2.53%, respectively). The warmest microhabitats were grasslands (23.23 ± 0.51°C), whereas the coolest microhabitats were forests (18.92 ± 0.41°C). The distinct microclimate of dwarf shrubs was cooler (21.46 ± 0.41°C) and moister (5.43 ± 0.53%) than the surrounding semi-desert like grassland. Furthermore, we found a different spider community composition and trait state composition of spiders in forests, edges, grasslands and dwarf shrub microhabitats. Forests (9.90 ± 0.95) and edges (11.44 ± 1.27) hosted a higher species richness than grasslands (7.08 ± 4.27) and dwarf shrubs (5.09 ± 1.33). We collected larger spiders on the edges than in dwarf shrub microhabitats. The dwarf shrubs hosted a different microclimate and spider community composition from the grassland. Climate change in the forest-steppe region is assumed to be driven by a combination of warming and drying. In the coming decades, drought frequency and severity are predicted to increase. Woody vegetation, even dwarf shrubs, creates a thermal and moisture heterogeneity that might aid arthropods in buffering macroclimatic warming through behavioural thermoregulation. Therefore, their presence on grasslands can benefit the conservation of specialised grassland arthropods.

Changes in community composition and prey capture of web-building spiders during rice field development

Understanding the effects of microhabitat changes on arthropod predator communities and their prey in agroecosystems is essential for field management and biocontrol. Few studies have investigated the trait composition of web-building spider communities in rice ecosystems. Here, we examined how temporal changes during the rice field development affect the abundance and traits of orb-web spiders, and how these effects consequently influence captured prey number and prey composition in irrigated rice ecosystems in southern Thailand. We used structural equation models to evaluate direct and indirect, spider-mediated effects of rice field development on captured prey numbers in each different guild. We found that the number of horizontal web-building spiders decreased during the rice field development, whereas there was no significant change in number of vertical web-building spiders. The number of captured detritivorous insects was positively related to the numbers of horizontal and vertical web-building spiders, while phytophagous insects and others were positively related only to the numbers of vertical web-building spiders. Moreover, the prey number captured by vertical web-building spiders seems to be indirectly increased through the decreasing number of horizontal web-building spiders in the late rice season. A fourth-corner analysis showed that spider species identity, spider traits (web type, web height and web diameter), vegetation height, and water level generally influenced the prey captured by web-building spiders. Horizontal web-building spider species with lower web placement during the flooding phase captured high numbers of detritus-feeding insects, while vertical web-building spider species with higher web placement captured high numbers of rice pests, predators and others. Our results suggest that the field development acted as an environmental factor that determined the species identity and traits of web-building spider communities. The findings of this study can help to predict the ecosystem services provided by the web-building spider community in rice ecosystems.

Distance decay effects predominantly shape spider but not carabid community composition in crop fields in north-western Europe

Agricultural intensification and expansion are regarded as main drivers of biodiversity loss. This conclusion is mainly based on observed declines of local diversity (α-diversity), while effects on community composition homogenization (decrease of β-diversity) at a larger spatial scale are less well understood. Carabid beetles and spiders represent two widespread guilds and are important predators of pest species. Here we surveyed carabid beetles and spiders in 66 winter wheat fields in four northwestern European countries (Germany, the Netherlands, Sweden and UK) and analyzed how their community composition was related to geographic distance (separation distance between any pairwise fields) and three environmental variables: crop yield (proxy for land-use intensity), percentage cropland (proxy for landscape complexity) and soil organic carbon content (proxy for local soil conditions). We further analyzed whether the relationship between carabid beetle and spider community composition and geographic distance was influenced by environmental variables. We found that, 55 % and 75 % of all observed carabid and spider individuals, respectively, belonged to species that occurred in all four countries. However, individuals of species that were unique to a particular country only accounted for 3 % of all collected individuals for both taxa. Furthermore, we found a negative relationship between distance and similarity of spider communities but not for carabid beetle communities. None of the environmental variables were related to similarity of carabid beetle and spider communities, nor moderated the effects of distance. Our study indicates that across a great part of the European continent, arthropod communities (especially carabid beetles) in agricultural landscapes are composed of very similar species that are robust to current variations in environment and land-use.

Vegetation Affects the Responses of Canopy Spider Communities to Elevation Gradients on Changbai Mountain, China.

Forest canopies, an essential part of forest ecosystems, are among the most highly threatened terrestrial habitats. Mountains provide ideal conditions for studying the variation in community structure with elevations. Spiders are one of the most abundant predators of arthropods in terrestrial ecosystems and can have extremely important collective effects on forest ecosystems. How the diversity and composition of canopy spider communities respond to elevation changes in temperate forests remains poorly understood. In this study, we collected canopy spiders from four elevation sites (800 m, 1100 m, 1400 m, and 1700 m) on Changbai Mountain using the fogging method in August 2016. With the methods of ANOVA analysis, transformation-based redundancy analysis, and random forest analysis, we explored the responses of canopy spider communities to elevation. In total, 8826 spiders comprising 81 species were identified and the most abundant families were Thomisidae, Clubionidae, Linyphiidae, and Theridiidae (77.29% of total individuals). Species richness decreased whereas evenness increased with increasing elevation, indicating that elevation has an important impact on community structure. The pattern of absolute abundance was hump shaped with increasing elevation. We found that the community compositions at the three taxonomic levels (species, family, and guild) along the elevation gradient were obviously altered and the variation in community composition was higher at low-elevation sites than at high-elevation sites. There were 19 common species (23.46%) among the four elevations. Regression and RDA results showed that vegetation variables contributed to the variation in the diversity and composition of canopy spiders. Furthermore, the influence of factors would be weakened with the taxonomic level increasing. Therefore, our findings greatly highlight the important role of vegetation in the diversity and composition of canopy spiders and the influence is closely related to the taxonomic level.

Urban Heat Island and Reduced Habitat Complexity Explain Spider Community Composition by Excluding Large and Heat-Sensitive Species

Along with worldwide urbanization, upheavals in habitat and temperature are major threats for biodiversity. However, due to their interdependence, their relative roles as drivers of animal community composition remain entangled. Here, we investigated how taxonomic and functional compositions of arthropod communities were related to uncorrelated habitat and temperature gradients, and compared landscape (i.e., urbanization, Urban Heat Island (UHI)) to local variables (i.e., vegetation height and cover, near-ground temperature). We sampled 20,499 spiders (137 species) on 36 grasslands in Rennes (northwestern France). Unlike rural areas, urban sites were characterized by short vegetation and intense UHI, hosted species-poor communities, and were composed of small thermophilic species. UHI intensification and local loss of habitat complexity (short and dense vegetation) were associated with declining large and heat-sensitive species. These results highlight the prevalent role of urban warming, rather than land cover change, as an urban filter. Further, we show that landscape-scale UHI, not local temperature, filters species according to their functional attributes. UHI can therefore be considered as a thermal barrier, filtering species according to their physiological capacity to cope with urban thermal conditions. Finally, to counterbalance biotic homogenization, we argue for the importance of implementing complex habitat structures at the local scale within urban green infrastructure.

Sensitivity of spiders from different ecosystems to lambda-cyhalothrin: effects of phylogeny and climate.

In spite of their importance as arthropod predators, spiders have received little attention in the risk assessment of pesticides. In addition, research has mainly focused on a few species commonly found in agricultural habitats. Spiders living in more natural ecosystems may also be exposed to and affected by pesticides, including insecticides. However, their sensitivity and factors driving possible variations in sensitivity between spider taxa are largely unknown. To fill this gap, we quantified the sensitivity of 28 spider species from a wide range of European ecosystems to lambda-cyhalothrin in an acute exposure scenario. Sensitivity varied among the tested populations by a factor of 30. Strong differences in sensitivity were observed between families, but also between genera within the Lycosidae. Apart from the variation explained by the phylogeny, spiders from boreal and polar climates were more sensitive than spiders from warmer areas. Overall, the median lethal concentration (LC50 ) of 85% of species was below the recommended application rate of lambda-cyhalothrin (75 ng a.i. cm-2 ). Our study underlines the high sensitivity of spiders to lambda-cyhalothrin, which can lead to unintended negative effects on pest suppression in areas treated with this insecticide. The strong differences observed between families and genera indicate that the functional composition of spider communities would change in affected areas. Overall, the variation in spider sensitivity suggests that multispecies investigations should be more widely considered in pesticide risk assessment. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Tree species identity, canopy structure and prey availability differentially affect canopy spider diversity and trophic composition

Forest canopies maintain a high proportion of arthropod diversity. The drivers that structure these communities, however, are poorly understood. Therefore, integrative research connecting tree species identity and environmental stand properties with taxonomic and functional community composition of canopy arthropods is required. In this study, we investigated how the taxonomic, functional and trophic composition of arboreal spider communities is affected by tree species composition and associated differences in canopy structure and prey availability in temperate forests. We sampled canopy spiders as well as their potential prey using insecticidal fogging in monospecific and mixed stands of native European beech, native Norway spruce and non-native Douglas fir. Trophic metrics were obtained from stable isotope analysis and structural canopy properties were assessed with mobile laser scanning. Monospecific native spruce stands promoted local canopy spider abundance and diversity, but native beech and beech–conifer mixtures had the highest diversity at landscape scale. Spider community composition differed between monospecific stands, with broadleaf–conifer mixtures mitigating these differences. Irrespective of tree species identity, spider abundance, taxonomic diversity, functional richness and isotopic richness increased in structurally heterogeneous canopies with high prey abundances, but functional evenness and trophic divergence decreased. Our study shows that canopy spiders are differentially affected by tree species identity, canopy structure and prey availability. Broadleaf–conifer mixtures mitigated negative effects of (non-native) conifers, but positive mixture effects were only evident at the landscape scale. Structurally heterogeneous canopies promoted the dominance of only specific trait clusters. This indicates that intermediate heterogeneity might result in high stability of ecological communities.

Heather (Calluna vulgaris) supports spider diversity of oligotrophic peat bogs

The heterogeneity of microhabitats is an important driver of biodiversity. Therefore, conserving habitat heterogeneity at multiple spatial scales is essential to biodiversity conservation. This study investigates the effect and the conservation value of micromosaic heterogeneity provided by the heather (Calluna vulgaris) patches in an Eastern-European peat bog on the spider communities. We found that the heather patches strongly affect spiders; the species richness and abundance were higher in heather than in open bogs. Heather shrubs form a separate special microhabitat, which differs in structure, microclimate and litter quality, and has a significant positive effect on diversity of spiders. Furthermore, we collected smaller spiders and more web builders in heather sites than in control sites, presumably due to the different microhabitat structures and prey availability. However, habitat type did not affect the vertical microhabitat preference of spiders. The species composition of spider communities differed between the two microhabitat types. We identified seven significant indicator species in heather shrubs, whereas three species were significant indicators of control sites. The species richness and the presence of rare and endangered peat bog specialist spider species in heather patches highlight the high conservation value of peat bogs.

Composition, abundance and biodiversity of terrestrial arthropods in pastures and their relationship with landscaping plants

We investigated the association of landscaping plants with the communities of ground-dwelling arthropods within pastures and tested the hypothesis that arthropod biodiversity increases with vegetation heterogeneity. The community characterization and biodiversity of arthropods in a pasture were compared with those within communities with landscaping plants, including forest remnants, Forsythia koreana and Prunus serotina. The total abundance of mites was greater within the forest remnants than within the pasture; however, the abundance of insects and spiders did not differ. Nonmetric multidimensional scaling and the multiresponse permutation procedure revealed that the community composition of insects and spiders differed according to vegetation type. The abundance of Teleogryllus emma was highest within the forest remnant community, which suggested the species’ dependency on vegetation type. Species richness and the Shannon index of insects increased within F. koreana but not within P. serotina compared with the pasture. This suggested that belts of shrubs might have a greater promoting effect on insect biodiversity than belts of trees. Species richness of spiders did not differ by vegetation type. The total number of insect and spider species within the study area increased by 2.8 and 3.5 times, respectively, by establishing three types of vegetation. These results suggested that increasing vegetation heterogeneity by establishing landscaping plants is a good option for conserving insect and spider biodiversity in pastures.

Species composition of shoreline wolf spider communities vary with salinity, but their diets vary with wrack inflow.

Wolf spiders are typically the most common group of arthropod predators on both lake and marine shorelines because of the high prey availability in these habitats. However, shores are also harsh environments due to flooding and, in proximity to marine waters, to toxic salinity levels. Here, we describe the spider community, prey availabilities, and spider diets between shoreline sites with different salinities, albeit with comparatively small differences (5‰ vs. 7‰). Despite the small environmental differences, spider communities between lower and higher saline sites showed an almost complete species turnover. At the same time, differences in prey availability or spider gut contents did not match changes in spider species composition but rather changed with habitat characteristics within a region, where spiders collected at sites with thick wrack beds had a different diet than sites with little wrack. These data suggest that shifts in spider communities are due to habitat characteristics other than prey availabilities, and the most likely candidate restricting species in high salinity would be saline sensitivity. At the same time, species absence from low-saline habitats remains unresolved.

The effect of seabird presence and seasonality on ground-active spider communities across temperate islands.

Seabirds influence island ecosystems through nutrient additions and physical disturbance. These influences can have opposing effects on an island's invertebrate predator populations. Spiders (order: Araneae) are an important predator in many terrestrial island ecosystems, yet little is known about how seabird presence influences spider communities at the intraisland scale, or how they respond to seasonality in seabird colony attendance.We investigated the effects of seabird presence and seasonality on ground-active spider community structure (activity-density, family-level richness, age class, and sex structure) and composition at the family-level across five short-tailed shearwater breeding islands around south-eastern Tasmania, Australia. Using 75 pitfall traps (15 per island), spiders were collected inside, near, and outside seabird colonies on each island, at five different stages of the short-tailed shearwater breeding cycle over a year. Pitfall traps were deployed for a total of 2674 days, capturing 1592 spiders from 26 families with Linyphiidae and Lycosidae the most common. Spider activity-density was generally greater inside than outside seabird colonies, while family-level richness was generally higher outside seabird colonies. For these islands, seabird breeding stage did not affect activity-densities, but there were some seasonal changes in age class and sex structures with more adult males captured during winter. Our results provide some of the first insights into the spatial and temporal influences seabirds have on spider communities. We also provide some of the first records of spider family occurrences for south-eastern Tasmanian islands, which will provide an important baseline for assessing future change.

Microhabitat conditions affect web-building spider communities and their prey independent of effects of short-term wildlife fencing on forest vegetation

Spiders play a key role in forest food webs, where they regulate decomposer populations and may act as predators of pests and disease vectors. Spider community composition is determined in part by vegetation structure. Therefore, the exclusion of large mammals, such as deer and wild boar, through wildlife fencing may affect the composition of spider communities and their prey in forest ecosystems. Web-building spiders and their prey were hand-collected in plots that had been fenced for three years, as well as adjacent unfenced plots in a mixed temperate forest in north-eastern Germany. Additionally, spiders in the leaf litter were sampled in fenced and unfenced subareas by sieving litter. Wildlife fencing did not significantly affect spider densities or community composition per microhabitat. However, fencing affected the cover of different microhabitats significantly as there was a higher density of larger trees and higher leaflitter cover in fenced plots while there was a higher percentage of bare ground and deadwood in unfenced plots. Spider communities and their prey composition differed significantly between microhabitats (deciduous trees, coniferous trees, dead wood, understory vegetation, leaf litter) independent of fencing. Thysanoptera prey was mainly caught by spiders on coniferous trees and in the understory vegetation. Heteroptera prey were captured most frequently in the understory vegetation while Hymenoptera (excl. Formicidae) prey were mostly caught on deciduous trees. Several spider species showed a preference between deciduous and coniferous trees in the mixed forest. Wildlife fencing alters the vegetation structure of mixed forests and has indirect effects on spider communities and their role in forest food webs due to alteration of microhabitat availability.

Rainforest conversion to rubber and oil palm reduces abundance, biomass and diversity of canopy spiders.

Rainforest canopies, home to one of the most complex and diverse terrestrial arthropod communities, are threatened by conversion of rainforest into agricultural production systems. However, little is known about how predatory arthropod communities respond to such conversion. To address this, we compared canopy spider (Araneae) communities from lowland rainforest with those from three agricultural systems in Jambi Province, Sumatra, Indonesia, i.e., jungle rubber (rubber agroforest) and monoculture plantations of rubber and oil palm. Using canopy fogging, we collected 10,676 spider specimens belonging to 36 families and 445 morphospecies. The four most abundant families (Salticidae N = 2,043, Oonopidae N = 1,878, Theridiidae N = 1,533 and Clubionidae N = 1,188) together comprised 62.2% of total individuals, while the four most speciose families, Salticidae (S = 87), Theridiidae (S = 83), Araneidae (S = 48) and Thomisidae (S = 39), contained 57.8% of all morphospecies identified. In lowland rainforest, average abundance, biomass and species richness of canopy spiders was at least twice as high as in rubber or oil palm plantations, with jungle rubber showing similar abundances as rainforest, and intermediate biomass and richness. Community composition of spiders was similar in rainforest and jungle rubber, but differed from rubber and oil palm, which also differed from each other. Canonical Correspondence Analysis showed that canopy openness, aboveground tree biomass and tree density together explained 18.2% of the variation in spider communities at family level. On a morphospecies level, vascular plant species richness and tree density significantly affected the community composition but explained only 6.8% of the variance. While abundance, biomass and diversity of spiders declined strongly with the conversion of rainforest into monoculture plantations of rubber and oil palm, we also found that a large proportion of the rainforest spider community can thrive in extensive agroforestry systems such as jungle rubber. Despite being very different from rainforest, the canopy spider communities in rubber and oil palm plantations may still play a vital role in the biological control of canopy herbivore species, thus contributing important ecosystem services. The components of tree and palm canopy structure identified as major determinants of canopy spider communities may aid in decision-making processes toward establishing cash-crop plantation management systems which foster herbivore control by spiders.

Four-year study of arthropod taxonomic and functional responses to a forest wildfire: Epigeic ants and spiders are affected differently

When studying forest disturbances, it is essential to examine biodiversity from different perspectives, which includes considering its taxonomic and functional facets. Indeed, different taxa may respond differently based on their functional traits. We analyzed the short-term effects of a wildfire on epigeic ant and spider communities in a Mediterranean forest. We specifically hypothesized that (1) fire would initially decrease the taxonomic and functional diversity of both taxonomic communities and have a more pronounced effect on spiders than ants because spider nests are shallower than ant nests and are consequently more vulnerable to fire; (2) recovery time would be longer for spiders than ants; and (3) the responses of taxonomic and functional diversity would be dependent on the identities and functional traits of the species found in both taxa. Our results show that wildfire affected the structure and composition of both communities but had a greater influence on ants. Over the four years of the study, these effects were largely constant for ants, whereas spiders displayed recovery. The two facets of diversity showed parallel responses to fire in the structure and composition of ant communities and in the composition of spider communities. However, the taxonomic and functional structure of spider communities reacted differently. In both spiders and ants, we observed that burned plots hosted species typical of open habitats, while unburned plots hosted species typical of vegetated habitats. We highlight the importance of (1) conducting long-term post-fire monitoring to get an accurate estimate of ecosystem recovery relative to pre-fire conditions and (2) studying taxonomic and functional responses to fire in different taxa to increase the power of the ecosystem response predictions used in habitat management decisions.

Shade tree isolation in pastures modulates diversity of epiphyte‐dwelling spiders: The role of epiphyte biomass and species dispersal capacity

Abstract In Mexico, most forest habitats have been lost, leaving mostly agroecosystems such as coffee plantations. In some areas, coffee plants are commonly planted under a closed canopy of shade trees and sometimes these coffee plantations are transformed into cattle pastures, in which scattered and isolated trees remain. Isolated trees (i.e. trees without contact between their crowns) left in disturbed environments such as pastures represent an extreme of habitat reduction for tree‐dwelling organisms. However, these isolated trees can also be biodiversity reservoirs, serving as regeneration nuclei and connection points between terrestrial habitats. In this study, we evaluated whether the alpha and beta diversities of epiphyte‐dwelling spiders differ between isolated trees in a pasture and shade trees (i.e. which sustain a continuous canopy above the crop) in a coffee plantation, and whether epiphyte biomass and differences in the dispersal capacity of the spider species could explain these changes. We found that spider alpha diversity was almost 50% higher in isolated trees than in shade trees. Isolated trees had the highest epiphyte biomass and there was a positive relationship between spider diversity and epiphyte biomass in these trees but not in shade trees. Spider community composition differed between tree conditions. We found that compositional similarity decreased and turnover increased with distance between trees only for spiders with low dispersal capacity in isolated trees. The high subset of unique species and high species richness in isolated trees highlight their importance in preserving spider communities in agrolandscapes.

Ground-dwelling Spider Communities Respond to Changes in Riparian Vegetation Widths.

Spiders play a key role in the ecological dynamics in riparian habitats. However, most studies on the effects of changes in riparian habitats on spider communities have focused on the conversion of riparian forest to other land uses rather than on a gradient of forest widths. We assessed the community structure of ground-dwelling spiders in riparian vegetation fragments with varying widths in Southern Brazil. We selected four fragments with different riparian vegetation widths (> 40 m; < 30 m; < 15 m; < 5 m). In each fragment, spiders were seasonally collected using pitfall traps. We tested the effects of riparian vegetation widths and environmental variables (litter height, litter cover and canopy openness) on the taxonomic and guild composition of spider communities. The taxonomic and guild composition of ground-dwelling spiders varied among the widest (> 40 and < 30 m) and narrower riparian widths (< 15 m and < 5 m). While hunting spiders were associated with the narrower widths, web-building spiders were associated with the wider widths. Spider composition was influenced by the leaf litter height in the widest widths (> 40 and < 30 m) and by canopy openness in the narrowest width (< 15 m). Reductions in riparian vegetation were associated with significant changes in the community structure of ground-dwelling spiders, likely through top-down mechanisms associated with the higher litter input in wider fragments. In summary, the fragmentation of the riparian forests of Sothern Brazil are negatively associated with web-building spiders.

Landscape- and time-dependent benefits of wildflower areas to ground-dwelling arthropods

Wildflower areas are a popular agri-environment scheme to counteract agro-biodiversity loss. Yet, their benefits are controversially discussed. Since inconsistent benefits may be owed to landscape context and temporal dynamics, we applied a multi-year study to unravel effects of permanent and transient habitats on ground-dwelling arthropods in wildflower areas and cereal fields.Across three consecutive years, we studied activity density, species richness and community composition of rove beetles, carabid beetles and spiders in ten pairs of wildflower areas and cereal fields along independent gradients of proportions of permanent semi-natural habitats or transient wildflower areas.Arthropod responses to the proportions of permanent semi-natural habitats often followed a hump-shaped pattern, whereas transient wildflower areas seemed to drive linear responses. An interactive effect on rove beetle richness in wildflower areas implies that benefits were highest either at intermediate proportions of permanent semi-natural habitats or at lower proportions, but with additional availability of transient wildflower areas or in landscapes with low proportions of permanent semi-natural habitats, but high proportions of wildflower areas. However, ground-dwelling arthropod activity density or species richness did not systematically increase over the three study years.Our results suggest that both permanent and transient habitats differ in how they affect biodiversity, possibly due to different temporal continuity and resource diversity. Benefits of permanent semi-natural habitats seemed highest at an equilibrium between an increasing resource-related species pool and an increasing diversity dilution, whereas benefits of transient wildflower areas seemed to increase with resource complementarity and connectivity at the landscape scale. Nevertheless, both habitats seem to complement each other and considered in concert, seem to be most effective in promoting benefits of wildflower areas to ground-dwelling arthropods at intermediate landscape complexity. The substantial variation in diversity patterns among years with weather extremes, suggests that optimizing benefits of wildflower areas requires further multi-year studies.

Beta Diversity along an Elevational Gradient at the Pico da Neblina (Brazil): Is Spider (Arachnida-Araneae) Community Composition Congruent with the Guayana Region Elevational Zonation?

Beta diversity is usually high along elevational gradients. We studied a spider community at the Pico da Neblina (Brazil), an Amazonian mountain which is one of the southern components of the Guayana region. We sampled six elevations and investigated if beta diversity patterns correspond to the elevational division proposed for the region, between lowlands (up to 500 m), uplands (500 m to 1500 m), and highlands (&gt;1500 m). Patterns of dominance increased with elevation along the gradient, especially at the two highest elevations, indicating that changes in composition may be accompanied by changes in species abundance distribution. Beta diversity recorded was very high, but the pattern observed was not in accordance with the elevationaldivision proposed for the region. While the highlands indeed harbored different fauna, the three lowest elevationshad similar species compositions, indicating that the lowlands spider community extends into the uplands zone. Other measures of compositional change, such as similarity indices and species indicator analysis, also support this pattern. Our results, in addition to a revision of the literature, confirm the high diversity and endemism rates of montane spider communities, and we stress the importance of protecting those environments, especially considering the climate crisis.

Invasive Plants Differentially Impact Forest Invertebrates, Providing Taxon-Specific Benefits by Enhancing Structural Complexity

Exotic plant species often negatively affect native herbivores due to the lack of palatability of the invading plant. Although often unsuitable as food, certain invasive species may provide non-nutritional ecological benefits through increased habitat structural complexity. To understand the potential for common invasive forest plant species of the eastern United States to benefit invertebrate communities, we examined the functional and taxonomic community composition of forest insects and spiders in long-term monitoring plots that contained invasive plant species. The extent of invasive plant species ground cover significantly altered spider community composition as categorized by hunting guild. Areas with higher invasive herbaceous and grass cover contained a higher abundance of space web-weaving and hunting spiders, respectively. Spider species richness and total invertebrate abundance also increased with greater invasive grass cover. Still, these trends were driven by just two invasive plant species, garlic mustard and Japanese stiltgrass, both of which have previously been shown to provide structural benefits to native invertebrate taxa. While these two species may improve the structural component of understory forest habitat, many invertebrate groups were not significantly correlated with other prevalent invasive plants and one species, mock strawberry, negatively affected the abundance of certain insect taxa. Particularly in forests with reduced native plant structure, invasive plant management must be conducted with consideration for holistic habitat quality, including both plant palatability and structure.

Disturbance by invasive pathogenic fungus alters arthropod predator-prey food-webs in ash plantations.

According to the disturbance-succession theory, natural disturbances support biodiversity and are expected to increase the complexity of food-webs in forest ecosystems by opening canopies and creating a heterogeneous environment. However, a limited number of studies have investigated the impact of disturbance by invasive pathogenic species and succession on arthropod predator-prey food-webs in forest ecosystems. Hymenoscyphus fraxineus is a pathogenic fungus of ash trees that is invasive in Europe and causes massive dieback, mainly of the common ash Fraxinus excelsior across its native range. Here we investigated how this pathogenic fungus affects food-webs of web-building spiders and their prey in understorey vegetation of ash plantations. In 23 young and middle-aged ash plantations that were distributed along a gradient of infestation by H. fraxineus (29%-86% infestation), we measured the vegetation structure (canopy openness, shrub coverage, herb/grass coverage), the trait composition of local spider communities (web type, body size), the prey availability and the prey intercepted by spider webs. We then evaluated the multivariate prey composition (prey type, body size) and network properties. Hymenoscyphus fraxineus opened the ash tree canopy, which resulted in denser shrub coverage. The dense shrub vegetation changed the composition of web types in local spider communities and increasing fungus infestation resulted in reduced mean body size of spiders. Infestation by H. fraxineus reduced the availability of predaceous Coleoptera and increased the availability of herbivorous Coleoptera as potential prey. The mean body size of captured prey and the per capita capture rates of most prey groups decreased with increasing fungus infestation. Hymenoscyphus fraxineus infestation indirectly reduced the complexity in bipartite networks and the trophic functional complementarity in local web-building spider communities. The plantation age affected the vegetation structure but did not affect the studied food-webs. Forest disturbance by the invasive pathogen affected four trophic levels (plant-herbivore-coleopteran intermediate predator-top predator web-building spiders) and, contrary to the disturbance-succession theory, disturbance by the fungus simplified the web-building spider-prey food-webs. The results support the view that H. fraxineus represents a threat to the biodiversity and ecosystem functioning in the simplified ecosystems of ash plantations.