Impacts of exotic spider spillover on resident arthropod communities in a natural habitat

1. The spillover of exotic predators from managed ecosystems into natural habitats may exacerbate the biodiversity losses caused by land‐use intensification. 2. In the present study, the impacts of the exotic wandering spider Cheiracanthium mildei L. Koch in an oak woodland ecosystem adjacent to an intensively‐managed agricultural system were examined. 3. Abundance and species richness of resident spiders and insects in oak branches were reduced in the presence of C. mildei. Contrary to expectations, C. mildei did not disproportionately affect other wandering spider species, but appeared to impact spiders from all tested functional groups. Numbers of herbivorous and predatory insects were also lower in the presence of C. mildei. 4. Although the apparent effects of this spider extend to multiple trophic levels in oak woodland, its voracity and relatively large size may ultimately strengthen herbivore suppression in the vineyard–oak woodland landscape.     

Prey availability,pesticides and the abundance of orchard spider communities

In a 4 year study, in southern England, the abundance of apple orchard canopy spiders and their potential prey was manipulated using two pest management strategies based on broad spectrum (highly toxic both to spiders and pests) and selective (moderately toxic to spiders but highly toxic to pests) insecticides in the first part of the growing season. The spider community was left to develop freely afterwards. Apple orchard plots untreated by pesticides served as control.The effect of insecticides was detrimental to spider populations as the treatments coincided with the peak abundance of adults in May and early June. Within adults, the treatments were harmful to female spiders, whereas, male spiders were much less affected. As a result the proportion of males increased in all of the sampled spider families.The use of selective insecticides resulted in a higher spider abundance compared to the use of broad spectrum compounds while the highest spider abundance was found in the pesticide free trees, i.e. three significantly different spider abundance levels were produced in spring. Spider abundance began to increase unequally between the treatments afterwards and became identical in the two pesticide treated plots due to the immigration of juveniles from surrounding habitats. However, a similar equalisation of abundance was not observed between the pesticide treated plots and untreated control. Analysing the abundance pattern of potential prey in the plots of the studied orchard we concluded that the post-disturbance increase in spider abundance was regulated by prey availability.     

Effects of ant competition and bird predation on the spider assemblage of a citrus grove

Characterizing intraguild interactions is key to improving understanding of food webs because they are major forces in the structuring of communities. Spiders are generalist predators with intermediate positions in the food web that establish intraguild interactions with ants and birds, which respectively compete with and prey on them. Research has also found interactions between birds and ants, potentially resulting in non-additive effects of both groups on arthropod assemblages, although studies of their combined impacts with tests for multiple-predator effects are scarce. We thus aimed to discern the relative effect of ants and birds on the spider assemblage of a citrus grove. We used a split-plot design to factorially exclude these groups over 2 years, preventing ants reaching the canopies by placing sticky bands around tree trunks, and birds by enclosing groups of trees in cages. We sampled spiders from the canopies (beating) and the ground (pitfalls) every 3 months, and we identified them to species. We found a strong influence of ants on the canopy spider assemblage, mainly through a negative effect on the families Araneidae and Theridiidae. Since spiders’ weights from ant-excluded and control trees were similar, these results suggest interference competition of ants on spiders rather than competitive exploitation. Bird exclusion did not affect the spider assemblage, contrasting with other studies reporting a marked predatory pressure of birds on spiders; nor were there any non-additive effects of ants and birds. Our findings show that spider assemblages are not uniformly affected by intraguild competitors.     

Short‐term effects of low intensity fire on soil macroinvertebrate assemblages in different vegetation patch types in an Australian tropical savanna

Abstract Early dry season fires are a common land management regime employed across the tropical savannas of northern Australia. The rationale is that this reduces fuel loads and so reduces fire risk in the latter part of the dry season. Despite the acceptance of fire as a major management tool the ecological effects of fire remain uncertain. Vegetation patches and their associated macroinvertebrates play a critical role in the capture and recycling of water and nutrients. The aim of this study was to examine the responses of soil macroinvertebrates, within different types of vegetation patches, to early dry season fires in tropical savanna woodland in northern Australia. The abundance of major macroinvertebrate taxa and functional groups, and taxon richness were quantified in three vegetation patch types 2 weeks before and 2 weeks after burning. Termites dominated the soil macroinvertebrate assemblage sampled. Fire led to significant decreases in ant and spider abundances and overall taxon richness. Functional group analyses showed significant overall declines in the abundances of macropredators and litter transformers. There were also interactions between fire and patch type; in tree patches, fire significantly reduced total macroinvertebrate abundance, as well as the abundance of termites and ecosystem engineers. These changes in soil macroinvertebrates will potentially influence patch functionality, with important implications for soil processes and landscape health.     

Aerial dispersal ability does not drive spider success in a crop landscape

1. Although spiders can colonise ecosystems by air, dispersal capabilities differ among spider species. Web‐building spiders are thought to balloon at higher rates than hunting spiders. Spider success in agricultural systems may also depend on habitat preferences. Few studies have examined the success of aerially dispersing spiders in crop systems, and information about the dispersal capabilities of spiders in putative source habitats is limited. 2. Spiders were monitored in the air and on the foliage of vineyards and adjacent oak woodland in order to compare the aerial spider faunas between these disparate habitats and to determine whether highly dispersive species contributed disproportionately to the spider community in vineyards. 3. The results show that most aerially dispersing spiders in both habitats were web‐building dwarf spiders, Erigone spp. (Linyphiidae), although hunting spiders were also well represented in the air, especially in oak woodland. Most woodland spiders in the air appeared to be residents of oak woodland and probably dispersed only short distances. 4. Conversely, only a subset of the aerial spider fauna established in vineyards in high numbers. Spiders that dominated the aerial fauna were under‐represented on vineyard foliage, whereas several hunting spiders dispersed aerially at low rates but dominated vineyard spider composition. 5. These results suggest that aerial dispersal ability may allow spiders to reach crop systems, but that establishment depends on habitat preferences and/or competitive ability.     

Responses of ant communities to experimental fire regimes on rangelands in the Victoria River District of the Northern Territory

Abstract Fire is a significant feature of Australia's savannas. Its use is being encouraged for cattle rangeland management, but there is little knowledge of the ecological effects of prescribed fire regimes on native biodiversity. The responses of ant communities to five experimental fire regimes over 2 years are reported from the Victoria River District in the semi‐arid tropics of northern Australia. The experiment was stratified at two levels: soil type (red and black) and fire treatment (unburnt; burnt twice in successive years in early (May) or late (October) dry season and unburnt thereafter; and burnt twice, 3 years apart, in early or late dry season). Ants were sampled twice in April, corresponding with the end of the 1997 and 1998 wet seasons. Ant species richness was not responsive to fire treatment, but reduced with time since fire on black soil. Total ant abundance also reduced with time since fire on the black soil, with significant different abundances in burnt versus unburnt plots in the 1998 sample. Soil type and sampling time had the greatest influence on ant community composition in multivariate analysis than did fire regime, although there were moderate gradients of time since fire with the black soil plots. The abundance of 19 species were significantly different between fire regimes in anova , 13 on red soil and six on black soil. The abundance of eight species (four each on red and black soil) changed significantly with time since fire, with seven promoted by burning. Ant functional group profiles changed little with fire. Total ant abundance and richness had significant relationships with key pasture species and vegetative variables. The responses of ants largely recapitulated those of plants, birds and reptiles on the same plots. It is envisaged that ants will have an important role to play in the sustainable management of Australia's rangelands aiding the off‐reserve conservation of biodiversity.     

Effects of tree species diversity on a community of weaver spiders in a tropical forest plantation

The effects of producer diversity on predators have received little attention in arboreal plant communities, particularly in the tropics. This is particularly true in the case of tree diversity effects on web‐building spiders, one of the most important groups of invertebrate predators in terrestrial plant communities. We evaluated the effects of tree species diversity on the community of weaver spiders associated with big‐leaf mahogany (Swietenia macrophylla) in 19, 21 × 21‐m plots (64 plants/plot) of a tropical forest plantation which were either mahogany monocultures (12 plots) or polycultures (seven plots) that included mahogany and three other tree species. We conducted two surveys of weaver spiders on mahogany trees to evaluate the effects of tree diversity on spider abundance, species richness, diversity, and species composition associated with mahogany. Our results indicated that tree species mixtures exhibited significantly greater spider abundance, species richness, and diversity, as well as differences in spider species composition relative to monocultures. These results could be due to species polycultures providing a broader range of microhabitat conditions favoring spider species with different habitat requirements, a greater availability of web‐building sites, or due to increased diversity or abundance of prey. Accordingly, these results emphasize the importance of mixed forest plantations for boosting predator abundance and diversity and potentially enhancing herbivore pest suppression. Future work is necessary to determine the specific mechanisms underlying these patterns as well as the top‐down effects of increased spider abundance and species richness on herbivore abundance and damage.     

Influence of ground cover on spider populations in a table grape vineyard

1. Cover crops and/or resident ground vegetation have been used in California vineyards to increase the number of predators and decrease the number of pestiferous herbivores. The most common resident predators in vineyards are spiders (Araneae). Several observational studies suggest that the addition of cover crops results in an increase in spider density and a decrease in insect pest densities. 2. To test experimentally the effects of cover crops and/or resident ground vegetation (hereafter collectively referred to as ground cover) on spider populations, a 3-year study was undertaken in a commercial vineyard. Large, replicated plots were established with and without ground cover during the growing season. Spider species diversity was analysed on the vines and on the ground cover. 3. On the vines, there was no significant difference in spider species richness or the total number of spiders in plots with and without ground cover. There were differences in the relative abundance of two spiders between treatments, with one species (Trachelas pacificus [Chamberlin & Ivie]) more abundant in plots with ground cover and another (Hololena nedra Chamberlin & Ivie) more common on vines in plots with no ground cover. Annual variation in spider abundance was greater than variation due to ground cover treatment. 4. On the ground cover, the spider species diversity was considerably different from that found on the vines above, suggesting that there is little movement of spiders between the ground cover and the vines. Enhancement of T. pacificus populations on vines with ground covers may be a result of prey species movement between the ground cover and the vines. Spider abundance was sparse on the bare ground. 5. The maintenance of ground cover increased spider species diversity in the vineyard as a whole (vine and ground cover). However, the relatively small changes in spider abundance on the vines indicate there are limitations in the use of ground covers for pest management with respect to generalist predators.     

Big and aerial invaders: dominance of exotic spiders in burned New Zealand tussock grasslands

As post-disturbance community response depends on the characteristics of the ecosystem and the species composition, so does the invasion of exotic species rely on their suitability to the new environment. Here, we test two hypotheses: exotic spider species dominate the community after burning; and two traits are prevalent for their colonisation ability: ballooning and body size, the latter being correlated with their dispersal ability. We established spring burn, summer burn and unburned experimental plots in a New Zealand tussock grassland area and collected annual samples 3 and 4 years before and after the burning, respectively. Exotic spider abundance increased in the two burn treatments, driven by an increase in Linyphiidae. Indicator analysis showed that exotic and native species characterised burned and unburned plots, respectively. Generalised linear mixed-effects models indicated that ballooning had a positive effect on the post-burning establishment (density) of spiders in summer burn plots but not in spring plots. Body size had a positive effect on colonisation and establishment. The ability to balloon may partly explain the dominance of exotic Linyphiidae species. Larger spiders are better at moving into and colonising burned sites probably because of their ability to travel longer distances over land. Native species showed a low resilience to burning, and although confirmation requires longer-term data, our findings suggest that frequent fires could cause long lasting damage to the native spider fauna of tussock grasslands, and we propose limiting the use of fire to essential situations.     

Bird communities of dry forests and oak woodland of western Mexico

Bird species-richness and densities were studied in spring and autumn of 1991 and 1992 in dry forest and oak woodland in western Mexico. Classification of the vegetation resulted in the identification of six dry forest types: from thorn forests, dominated by Acacia , through broad-leaved tree forest (typical dry forest of western Mexico) and small-leaved tree forest to Ipomoea forest. Oak woodland and mixed woodland, which are a transition between dry forest and the more mesic oak woodland, formed two further forest types. In the study area as a whole, bird densities were higher in autumn, following the rainy season, than in spring, which is the dry season, and the beginning of the breeding season. Densities in the two autumns were very similar (mean 93 ± 7.8 birds per 2.8 ha) but differed significantly between spring 1991 (57 ± 2.2 per 2.8 ha) and spring 1992 (70 ± 3.2 per 2.8 ha), possibly due to unseasonal rain in 1992. In autumn, bird densities were highest in thorn forests and lowest in broad-leaved tree forests and oak woodland. In spring 1991, bird densities were highest in Prosopis thorn forest and mixed woodland, and lowest in oak woodland. Bird species-richness was low in oak woodland, in both seasons, and high in mixed woodland and Ipomoea forest in spring. Bird species composition between forest types was more similar in the spring than autumn. The spring similarity in species composition is explained by the presence of generalist species in times of food scarcity during the dry season, and by the homogeneity of the predominantly leafless vegetation. Comparison with the bird species composition of a dry forest in Venezuela and the Pacific coast of Mexico indicates that the sites in the present study have an intermediate number of species. Although the present study recorded a smaller number of bird species than on the Pacific coast, 16 were different, expanding the total for Mexican dry forest by 14% from 118 to 134.     

Relative impact of spider predation and cover crop on population dynamics of Erythroneura variabilis in a raisin grape vineyard

Experimental and correlative evidence has steadily mounted over the past 30 years implicating spiders in the suppression of insect herbivore pests in crop fields. A large body of evidence has also shown that increasing agroecosystem vegetation diversity often influences the abundance of herbivores and their natural enemies. In previous experiments, the abundance of several species of spiders on grapevines in a raisin grape vineyard was twofold enhanced in vineyard plots vegetationally diversified with a cover crop. A concomitant reduction in the abundance of the leafhopper pest Erythroneura variabilis Beamer was observed on grapevines in the diversified plots, but a causal relationship was not established. In the present study, we simultaneously manipulated spider densities (in open‐vine spider exclusion and vine‐shoot enclosures) and ground cover to determine their relative impact on E. variabilis population dynamics. Open‐vine spider exclusion resulted in an average 35% increase in the density of E. variabilis the greatest effect with occurring during the first and second leafhopper generations. The negative impact of spiders on E. variabilis densities was corroborated with vine‐shoot enclosure experiments. Under the conditions of the present study, the cover crop per se did not affect the dynamics of E. variabilis populations on grapevines, despite a 1.6‐fold increase in spider densities on vines in cover crop plots, compared with vines in bare ground plots, probably due to insufficient spider enhancement and low overall E. variabilis abundance during the summer months. The cover crop had little effect on vine macronutrient status (and presumably vine water status). While this study provided further support for the hypothesis that vegetation diversity can enhance spider abundance, this enhancement does not always lead to lower pest densities, thus underscoring the complexity and variability that exists in interactions involving cover crop, spiders, and crop plants and their herbivore pests.     

Do seed predation and dispersal limit downslope movement of a semi-desert grassland/oak woodland transition?

Abstract. Semi-desert grasslands and dryland forests are typically arranged along elevation gradients, with low elevation grasslands and savannas separated from higher-elevation woodlands by a diffuse boundary. Recent (< 200 yr) woody plant encroachment into adjacent semi-desert grasslands appears to be a cosmopolitan phenomenon, and has been attributed to disturbance by humans (e.g., livestock grazing, fire suppression); however, little is known about rates, patterns and mechanisms. Are observations of increased woody plant abundance in semi-arid grasslands indicative of a downslope shift in the boundary zone? Experimental plots were established in adjacent oak woodlands and semi-desert grasslands in southeastern Arizona, to determine if mechanisms of acorn predation and dispersal would facilitate or limit downslope movement of oak woodlands. We recovered acorns that had been dispersed 50 m into adjacent grasslands, which suggests that they were cached by acorn predators. Acorns in grassland plots were more than twice as likely to escape predation than acorns that remained in woodland or cleared woodland plots. Contrary to previously published research, simulated perturbations (gap formation, understory and below-ground vegetation removal) did not affect seed predation, suggesting that generalizations from mesic, deciduous oak forests may not be accurately extrapolated to xeric, evergreen oak forests. Recently published studies indicate that xeric conditions limit survival of oak seedlings across the boundary zone, suggesting that observed patterns of acorn dispersal and predation provide the potential for colonization of adjacent grassland only during infrequent years with cool, moist conditions during late summer months.     

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.     

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

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

Observations of responses to re‐introducing fire in a Basalt Plains grassland after the removal of grazing: Implications for restoration

Natural grasslands in southern Australia commonly exist in altered states. One widespread altered state is grassland pasture dominated by cool‐season (C3) native grasses maintained by ongoing grazing. This study explores the consequences of removing grazing and introducing fire as a conservation management tool for such a site. We examined the abundance of two native and three exotic species, across a mosaic of fire regimes that occurred over a three‐year period: unburnt, summer wild‐fire (>2 years previous), autumn management fire (<1 year previously) and burnt in both fires. Given that one aim of conservation management is to increase native species at the expense of exotics, the impacts of the fires were largely positive. Native grasses were at higher cover levels in the fire‐managed vegetation than in the unburnt vegetation. Of the three exotic species, one was consistently at lower density in the burnt plots compared to the unburnt plots, while the others were lower only in those plots burnt in summer. The results show that the response of a species varies significantly between different fire events, and that the effects of one fire can persist through subsequent fires. Importantly, some of the effects were large, with changes in the density of plants of over 100‐fold. Fire is potentially a cost‐effective tool to assist the ecological restoration of retired grassland pastures at large scales.     

Spiders as potential indicators of elephant‐induced habitat changes in endemic sand forest,Maputaland, South Africa

Elephant impacts on spider assemblages, and the potential use of spiders as indicators of habitat changes was assessed in central Maputaland, South Africa. Three habitats, namely undisturbed sand forest, elephant disturbed sand forest and mixed woodland, were sampled. To ensure a thorough representation of all spider guilds, spiders were collected by tree beating, sweep netting, active searching, leaf litter sifting and pitfall traps. In total, 2808 individual spiders, representing 36 families, 144 determined genera and 251 species were collected. Spider abundance was highest in the undisturbed sand forest (n = 1129, S = 179), followed by elephant disturbed sand forest (n = 1006, S = 165) and mixed woodland (n = 673, S = 171). Assemblages of the two sand forests were more similar than to the mixed woodland assemblage. Active hunting species were indicators of the more open vegetation of elephant disturbed sand forest (six active hunters, no web‐builders) and mixed woodland (ten active hunters, one web‐builder), whereas web‐builders are indicators of the dense, complex vegetation structure of undisturbed sand forest (six web‐builders, three active hunters). Elephant‐induced changes to the vegetation structure in this high diversity, high endemism region result in changes in the composition of spider assemblages, and may need to be mitigated by management intervention.     

Mitigating impacts of weeds and kangaroo grazing following prescribed fire in a Banksia woodland

Banksia woodlands are renowned for their flammability and prescribed fire is increasingly employed to reduce the risk of wildfire and to protect life and property, particularly where these woodlands occur on the urban interface. Prescribed fire is also employed as a tool for protecting biodiversity assets but can have adverse impacts on native plant communities. We investigated changes in species richness and cover in native and introduced flora following autumn prescribed fire in a 700‐hectare Banksia/Tuart (Eucalyptus gomphocephala) woodland that had not burnt for more than 30 years. Effectiveness of management techniques at reducing weed cover and the impacts of grazing by Western Grey Kangaroo (Macropus fuliginosus) postfire were also investigated. Thirty plots were established across a designated burn boundary immediately before a prescribed fire in May 2011, and species richness and cover were measured 3 years after the fire, in spring of 2013. Fencing treatments were established immediately following the fire, and weed management treatments were applied annually in winter over the subsequent 3 years. Our results indicate that autumn prescribed fire can facilitate increases in weed cover, but management techniques can limit the establishment of targeted weeds postfire. Postfire grazing was found to have significant adverse impacts on native species cover and vegetation structure, but it also limited establishment of some serious weeds including Pigface (Carpobrotus edulis). Manipulating herbivores in time and space following prescribed fire could be an important and cost‐effective way of maintaining biodiversity values.     

Limited benefits of non-crop vegetation on spiders in Australian vineyards: regional or crop differences?

In crops, invertebrate natural enemies such as spiders have been documented as responding to non-crop vegetation at the local and landscape scales, particularly in northern Europe. Much of this information is based on data from arable or annual crops and it is possible that spider numbers in more persistent perennial systems including vineyards may be less dependent on non-crop vegetation. To test the relationship between spider abundance and non-crop vegetation within the context of Australian vineyards, we sampled spiders in 54 vineyards with adjacent non-crop vegetation, from three different regions. Landscape composition in the area surrounding each of the 54 sites was characterized at 11 spatial scales from 95?m to 3?km radius and spiders were sampled monthly using canopy sticky traps and ground pitfall traps. There were only weak relationships between pasture or woody vegetation and the abundance of spiders in vineyards at all spatial scales. At the local scale, abundance of most spider families tended to be greater in vineyards with adjacent pasture. At the landscape scale there were inconsistent patterns. We discuss possible reasons for these apparent contrasting patterns between perennial and annual crops and European compared to Australian agroecosystems.     

Reducing predation of orb-web spiders by controlling common wasps (Vespula vulgaris) in a New Zealand beech forest

1. Introduced common wasps ( Vespula vulgaris ) reach high densities in the beech forests ( Nothofagus spp.) of the northern South Island, New Zealand, and may be having a severe impact on populations of native invertebrates. An experimental approach was used to test whether reducing the abundance of common wasps increases the probability of native invertebrates surviving. Garden orb-web spiders ( Eriophora pustulosa ) were used because they were easy to collect and could be trained to build webs on a standard frame. Thirty orb-web spiders were placed out on web-frames in each of four study sites in beech forest during periods of low, medium and high wasp abundance, and their rate of removal was measured over a 4-h period. Wasp numbers were reduced by poisoning in two study sites. Using wasp-abundance data from weekly Malaise trap samples in the poisoned and non-poisoned sites, the probability of spider survival over the entire wasp season was modelled and the level of wasp control necessary to protect natural populations of orb-web spiders was estimated.
2. Wasp abundance and the probability of spider survival were negatively correlated, and smaller spiders were likely to survive longer than larger spiders. At the peak of the wasp season, significantly more spiders survived in the poisoned areas than in the non-poisoned areas.
3. The probability of a spider surviving to the end of the wasp season was virtually nil in the non-poisoned sites (5.08 × 10^–18), but was also very unlikely in the poisoned areas (3.47 × 10^–5).
4. The survival model predicts that wasp abundance would need to be reduced by 80–89.5% over the entire wasp season to protect populations of orb-web spiders.
5. Extrapolation from the model predicts that the invertebrate taxa most vulnerable to wasp predation may have already been removed from the beech forest ecosystem during the 40 years of wasp occupation.