Interactions among young stages of the wolf spiders Pardosamoesta and P. mackenziana (Araneae: Lycosidae)

Young stages of the wolf spiders Pardosa moesta and P . mackenziana coexist on the forest floor in a deciduous forest in central Alberta, yet nothing is known of the potential interactions between and among these ubiquitous species. An experiment, using a series of 0.25-m² arenas, was designed to test for inter- and intraspecific exploitative competition. Experimental treatments were established in the arenas in late July. Treatments involved stocking recently hatched spiderlings of each species alone, and with both species together at natural (10 spiderlings per arena) and two times the natural densities. In September the arenas were searched for Pardosa spiderlings, and the survival and mass gain of each species were determined. Other predatory arthropods, and Collembola, a common prey of young wolf spiders, were counted in the arenas before the experimental treatments were established and at the end of the experiment. No evidence for competitive interactions was uncovered, but spiderling survival was 29% for P . moesta and 20% for P . mackenziana , suggesting other mortality factors (e.g., cannibalism, intraguild predation) may be important. Top-down effects (predatory arthropods) had no effect on Pardosa survival. Bottom-up effects, however, were significant as treatments containing spiderlings had fewer Collembola compared to control arenas, further supporting the importance of spiders in leaf-litter food webs.     

Tradeoffs involved in site selection and foraging in a wolf spider: effects of substrate structure and predation risk

Understanding how animals weigh habitat features, exposure to predators and access to resources is important to determining their life history and distribution across the landscape. For example, when predators accumulate in structurally complex habitats, they face an environment with different competitive interactions, foraging opportunities and predatory risks. The wolf spider Pardosa milvina inhabits the soil surface of highly disturbed habitats such as agricultural fields throughout eastern North America. Pardosa displays effective antipredator behavior in the presence of chemical cues produced by a larger coexisting wolf spider, Hogna helluo . We used those cues to simulate predation risk in laboratory and field experiments designed to test the effects of habitat substrate and predation risk on site selection and prey consumption of Pardosa . In general, Pardosa preferred more complex substrates over bare dirt but those preferences were eliminated or reversed when cues from Hogna were present. Feeding trials revealed that substrate alone had few effects on Pardosa prey consumption, which we measured by documenting the change in the abdomen width. Although the presence of Hogna cues reduced prey consumption overall in field feeding trials, the negative effect of predation risk on prey consumption was only observed in grass and bare dirt substrates in the laboratory. We also found that prey capture was negatively affected by habitat complexity for both spider species but that same complexity offered Pardosa protection from predation by Hogna. This study provides insight into how two predator species interact to balance site selection and feeding in order to avoid predation. Shifts in foraging and distributional patterns of predators can have profound implications for their role in the food web.     

Intra-guild predation relaxes natural enemy impacts on herbivore populations

Abstract. 1. To investigate the role of intra-guild predation in mediating the impact of the natural enemy complex on herbivore populations, a manipulative field experiment was conducted using uncaged plots (islets of Spartina cordgrass) on a North American salt marsh. The densities (moderate or low) of two invertebrate predators, the generalist wolf spider Pardosa littoralis and the specialist mirid bug Tytthus vagus , were manipulated in a 2 × 2 factorial design, and the resulting treatment effects on the population growth of their herbivorous prey, Prokelisia planthoppers, were assessed.
2. The abundance of wolf spiders on experimental islets was unaffected by the presence of mirid bugs, however the density of mirid bugs was influenced very negatively by the presence of the wolf spider.
3. The negative effect of the wolf spider on mirid bugs most probably resulted from the intra-guild predation of mirids by spiders because planthopper limitation by the wolf spider alone was significantly greater than when both predators were present.
4. As a result of intra-guild predation, planthopper population growth was positive in the presence of both predators, despite the fact that each predator alone promoted a decrease in planthopper population growth.
5. Notably, the occurrence of intra-guild predation diminished top-down impacts on planthopper populations in a relatively simple food web where strong top-down effects were expected. This result, however, was limited to habitats on the marsh with simply structured vegetation lacking leaf litter.     

Two ecologically-divergent generalist predators have different responses to landscape fragmentation

We conducted three replicated field experiments to test the population response of two ecologically-divergent wolf spider species ( Hogna helluo and Pardosa milvina ) to three correlates of landscape fragmentation: area reduction, spatial subdivision, and increased edge to core ratio. We selected these two species because they differ in vagility and habitat selectivity. Hogna helluo is relatively large, averse to disturbed substrata, and has poor colonization abilities. Conversely, Pardosa is small, vagile, and will use barren, disturbed areas. In a test for the effect of area reduction on populations of the two wolf spiders, we destroyed 0%, 20% or 80% of randomly selected habitat islands in replicated experimental landscapes. We found that population densities of Hogna declined significantly, even at the lowest level of area reduction (20%), and that there was an increase in numbers of Pardosa . In a test for the response to an increase in landscape subdivision, we created four levels of habitat fragmentation in replicate plots. We found a significant decline in Hogna populations with increasing fragmentation. Pardosa populations did not respond to the fragmentation. In the third experiment we kept landscape area and subdivision constant, but manipulated the edge-to-core ratio. We found that populations of Hogna declined sharply with increasing edge, and that populations of Pardosa did not respond. These two syntopic wolf spiders have distinctly different responses to landscape fragmentation.     

Wolf spider predator avoidance tactics and survival in the presence of diet-associated predator cues (Araneae: Lycosidae)

Some prey can distinguish between chemical cues from predators fed different diets. Here we document the first evidence of diet-based chemical discrimination of predators in a terrestrial arthropod and measure the survival value of behavioural responses to predator chemical cues. We tested activity level and avoidance behaviour of the wolf spider, Pardosa milvina, to faeces and silk associated with the predatory wolf spider, Hogna helluo, fed either P. milvina or crickets (Acheta domesticus). We then measured survival of Pardosa in the presence of Hogna when placed on blank paper or paper previously occupied by Hogna fed either crickets or Pardosa. Filter paper previously occupied by Hogna from each diet treatment or a blank control were simultaneously presented to adult female Pardosa among four treatment pairs (N=15/treatment): (1) blank paper/blank paper, (2) Hogna fed crickets/blank, (3) Hogna fed Pardosa /blank and (4) Hogna fed Pardosa / Hogna fed crickets. Cues from Hogna fed either crickets or Pardosa elicited significantly less activity relative to blank controls. Cues from Hogna fed Pardosa elicited a significantly greater reduction in activity than Hogna fed crickets. When given a choice, Pardosa initially chose the blank substrate significantly more often than either substrate with Hogna cues. Spiders survived longer in the presence of cues from either Hogna diet treatment relative to blank paper, but there was no significant effect of predator diet on survival. Results suggest diet-based predator cues elicit different levels of activity in Pardosa that reduce predation in the presence of Hogna. Copyright 2001 The Association for the Study of Animal Behaviour.     

The life-cycle of the Wolf spider Pardosa lugubris in Holland

Pardosa lugubris in Scotland has a 2-year life-cycle. In Holland the situation is less clear-cut: spiderlings emerging from the summer egg sac can reach sexual maturity by the following spring. These spiders, with a 1-year life-cycle, have one instar fewer than the Scottish spiders. The Dutch spiderlings from the autumn egg sac, like the Scottish spiders, have a 2-year life-cycle and have the same number of instars as the Scottish spiders.
The shorter life-cycle of some of the Dutch spiders is probably due to the fact that summer temperatures are higher in Holland than in Scotland. It is suggested that the length of the life-cycle may be an important factor in spider distribution and that this may account for the relative scarcity of large spider species in high latitudes.     

Foraging behaviour influences the outcome of predator–predator interactions

Abstract.  1. Interactions among predators may influence the total efficiency of a predator complex. The effect of intra- and interspecific interactions of the generalist predators Orthotylus marginalis (Heteroptera: Miridae) and Anthocoris nemorum (Heteroptera: Anthocoridae) was investigated in a laboratory experiment. Outcomes of the interactions were determined by comparing predation rates on eggs and larvae of the blue willow beetle Phratora vulgatissima of single individuals with those of two individuals of the same or different species.
2. A non-additive, antagonistic effect on predation rates due to intraspecific interactions was found between individuals of A. nemorum . No such effect was found in O. marginalis . These results are as expected as a consequence of differences in behaviour of the two predator species: A. nemorum is a much more active and mobile predator than O. marginalis .
3. Contrary to expectation, interspecific interactions between A. nemorum and O. marginalis did not affect the total predation rate.
4. An observation from the field corroborated the results obtained in the laboratory study; there was no negative relationship between the densities of the two predator species, indicating that the two species do not interact negatively in the field at their natural densities.
5. It is concluded that the additive effect of multiple predator species is of potential value in biological control.     

Kinship Influences Cannibalism in the Wolf Spider, Pardosa milvina

Recent studies have called into question the role of Wright's coefficient of relatedness (r) in the interactions among relatives. Kin selection theory predicts a positive relationship between relatedness and frequency of altruistic acts, but a number of researchers have reported the opposite relationship. I used a lycosid spider (Pardosa milvina) to test the hypothesis that genetic relatedness would affect the propensity of a cannibalistic species to prey on genetic relatives. I considered lack of predation to be a form of altruism where the predator incurs a cost (loss of a meal) that benefits potential prey. Specifically, I questioned whether direct genetic offspring would be avoided as prey items and whether the sex or reproductive condition of a cannibalistic predator would affect the likelihood of predation on conspecific juveniles. As predicted by kin selection theory, spiderling mothers ate significantly fewer of their own offspring than they did of nonkin spiderlings of the same age. Adult virgin female and adult male spiders ate significantly more spiders than females that had recently carried spiderlings. Females with egg sacs consumed significantly fewer spiderlings than did virgin female spiders. These findings support Hamilton's rule and suggest that, in some systems, genetic relatedness plays a strong role in governing altruistic behavior toward relatives.     

Early season natural control of the brown planthopper, Nilaparvata lugens: the contribution and interaction of two spider species and a predatory bug

Nilaparvata lugens St?l, the Brown Planthopper (BPH), is a major pest in rice. The lycosid Pardosa pseudoannulata (B?senberg & Strand) and the linyphiid Atypena formosana (Oi) are the early dominant predators in irrigated rice. Later, predatory bugs, including the mirid Cyrtorhinus lividipennis Reuter, become dominant. In unsprayed rice, BPH numbers normally remain low. While P. pseudoannulata is known to be a key natural enemy of BPH, the contribution to BPH reduction by the smaller A. formosana is less well known. Due to the size difference, A. formosana may also be an intraguild prey of P. pseudoannulata. To investigate predation on BPH by the two spider species alone, together and in combination with C. lividipennis, two cage experiments were conducted, the first with adult spiders, the second with immature/unmated spiders. In the latter, spiders were introduced with a delay to allow a better establishment of C. lividipennis. In both experiments, BPH numbers were lowest in treatments with more than one predator species present. Intermediate BPH reduction was obtained with P. pseudoannulata followed by A. formosana and C. lividipennis. While P. pseudoannulata can prey upon large nymphs and adult BPH, A. formosana favour early instar BPH, leading to a more even control across instars in treatments with both spider species. Pardosa pseudoannulata numbers increased more with A. formosana or A. formosana and C. lividipennis present. In contrast, P. pseudoannulata reduced A. formosana and C. lividipennis numbers. The presence of C. lividipennis apparently lessened intraguild predation on A. formosana and may be an intraguild prey of A. formosana. Competition for prey may have added to the antagonistic interactions found. From a biological control perspective, the presence of both spiders in early rice is an advantage for the biological control of BPH in rice. In early rice, results show that A. formosana is an important predator of BPH and, like C. lividipennis, can complement control by P. pseudoannulata and serve as intraguild prey for the latter species.     

Competition between the nymphs of two regionally co-occurring species of Notonecta (Hemiptera: Notonectidae)

1. Two species of freshwater invertebrate predator, Notonecta maculata and N. obliqua , showed a negative association in a series of small, man-made ponds in the Peak National Park, Derbyshire, U.K. The present study examines the potential role of interspecific interactions among nymphs on this regional distribution pattern.
2. The survival, development and feeding efficiency of nymphs were examined in laboratory and field mesocosm experiments with intra- and interspecific competition and contrasting environmental complexity.
3. Survival to adulthood and mean lifespan varied significantly in interspecific competition treatments in both laboratory and field experiments, with N . maculata showing higher survival in the simple environment and N. obliqua higher survival in the complex environment.
4. Variations in feeding efficiency were consistent with the survival trends: N. maculata had a higher efficiency in the simple environment, whereas N. obliqua had greater efficiency in the complex environment. There was evidence of a developmental response in feeding efficiency, with differences between species increasing with age.
5. These results suggest that the relative competitive abilities of the two species are affected by habitat complexity, and that competition between species may modify the species distribution where they co-occur.     

真水狼蛛幼蛛各龄期的形态特征和生长发育

幼蛛在蜘蛛的种群中占有很大比例。通过室内饲养。获得了不同龄期的真水狼蛛幼蛛。其体重、体长、背甲宽、步足长、眼域宽以及中斑下的条形纵斑长度都随着龄期的增大而增加。背甲宽和中斑下的条形斑纹长度可用来判断真水幼蛛的龄期。雌蛛的取食量大于雄蛛,高龄幼蛛大于低龄幼蛛。幼蛛在蜕皮时不取食,蜕皮后,取食量明显增加。     

Interactions among juveniles of two freshwater crayfish species and a predatory fish

Two freshwater crayfish species, Astacus astacus L. and Pacifastacus leniusculus Dana, co-occur in some Swedish lakes. Observational studies indicate that the introduced, North American species P. leniusculus may gradually replace the native A. astacus, but the mechanism behind the replacement is not known. This study examined the direct effects of interspecific competition between the crayfish, and indirect effects of competitive interactions and fish (European perch, Perca fluviatilis L.) predation. Three different experiments with young-of-the-year (YOY) crayfish were performed. P. leniusculus was strongly dominant over similar-sized A. astacus in interference competition for shelter in a laboratory experiment. However, in a 35-day experiment in outdoor pools, A. astacus growth and survival were about equally affected by interactions with conspecifics and P. leniusculus. In contrast, P. leniusculus was significantly more affected by intraspecific competition than by competition with A. astacus, suggesting asymmetric competition between the two species. The presence of perch in outdoor ponds with mixed-species groups of the two crayfish species resulted in considerably higher predation rates on A. astacus than on P. leniusculus. Both species showed strong antipredator responses to perch by increasing refuge use. I suggest that higher perch predation rates on A. astacus originate from P. leniusculus being the superior species in interspecific competition for shelter. Because of displacement from refuges, A. astacus individuals become more exposed to the predator. This indirect effect of interactions among the two cray-fish species and the predator may be important in the observed in situ replacement of A. astacus by P. leniusculus.     

A test of the hypothesis that a pathway of intraguild predation limits densities of a wolf spider

Abstract.  1. The high number of potential predatory interactions among the many arthropod generalist predators in terrestrial food webs makes exhaustive testing of interaction strengths by field experiments unfeasible. Thus, correlative patterns and laboratory observations of behaviour often form the basis of inferences about the strength of interaction pathways involving generalist predators (intraguild predation).
2. Previous research has revealed a negative correlation between survival of juvenile wolf spiders of the genus Schizocosa (Lycosidae) and densities of another abundant spider family, the Gnaphosidae.
3. Feeding trials in laboratory microcosms with a leaf-litter substrate revealed that gnaphosids prey on juvenile Schizocosa in a structurally complex habitat.
4. Gnaphosid densities were manipulated in two different field experiments, each conducted in a different year, in order to test directly the hypothesis that intraguild predation by gnaphosids limits densities of juvenile Schizocosa .
5. Reducing numbers of gnaphosids, and doubling their numbers to two times the mean natural density, had no impact on the survival of juvenile Schizocosa in either field experiment. This finding suggests that correlative patterns in nature and feeding trials in the laboratory may at times provide deceptively simple and potentially misleading generalisations about the strengths of interaction pathways in complex networks of generalist predators.     

Preference for Cannibalism and Ontogenetic Constraints in Competitive Ability of Piscivorous Top Predators

Occurrence of cannibalism and inferior competitive ability of predators compared to their prey have been suggested to promote coexistence in size-structured intraguild predation (IGP) systems. The intrinsic size-structure of fish provides the necessary prerequisites to test whether the above mechanisms are general features of species interactions in fish communities where IGP is common. We first experimentally tested whether Arctic char (Salvelinus alpinus) were more efficient as a cannibal than as an interspecific predator on the prey fish ninespine stickleback (Pungitius pungitius) and whether ninespine stickleback were a more efficient competitor on the shared zooplankton prey than its predator, Arctic char. Secondly, we performed a literature survey to evaluate if piscivores in general are more efficient as cannibals than as interspecific predators and whether piscivores are inferior competitors on shared resources compared to their prey fish species. Both controlled pool experiments and outdoor pond experiments showed that char imposed a higher mortality on YOY char than on ninespine sticklebacks, suggesting that piscivorous char is a more efficient cannibal than interspecific predator. Estimates of size dependent attack rates on zooplankton further showed a consistently higher attack rate of ninespine sticklebacks compared to similar sized char on zooplankton, suggesting that ninespine stickleback is a more efficient competitor than char on zooplankton resources. The literature survey showed that piscivorous top consumers generally selected conspecifics over interspecific prey, and that prey species are competitively superior compared to juvenile piscivorous species in the zooplankton niche. We suggest that the observed selectivity for cannibal prey over interspecific prey and the competitive advantage of prey species over juvenile piscivores are common features in fish communities and that the observed selectivity for cannibalism over interspecific prey has the potential to mediate coexistence in size structured intraguild predation systems.     

Root competition and elevated CO2: effects on seedling growth in Linum usitatissimum populations and Linum–Silene cretica mixtures

1. Root competition can be an important determinant of the performance of neighbours within plant populations and communities. Because plants often maintain larger root systems and allocate more of their carbon to root systems under elevated atmospheric CO₂ than they do at lower CO₂ concentrations, root–root interactions could play an increasingly important role in determining competitive outcomes among individuals and plant species as global CO₂ concentration continues to rise.
2. We established 12 pure stands of Linum usitatissimum (flax) and 12 mixed stands of Linum and its naturally co-occurring weed species Silene cretica in opaque plastic trays each filled with the same amount of nutrient-rich soil mix. In half of the trays from each of these stand types, vertical waterproof partitions separated the root systems of individual plants from each other to prevent root competition, while in the other half no partitions were present. Half of the trays from all treatments were allowed to grow under low atmospheric CO₂ concentration (320μll^–1) and the other half under elevated CO₂ (600μll^–1), in daylight growth chambers for 30 days from seedling emergence until harvest in mid-June. All trays received equal amounts of water so that soils in the low CO₂ treatment were maintained at field capacity.
3. Our results indicate that under high soil fertilities: (1) intra-specific root–root interactions alone play a relatively insignificant role in determining plant biomass production within pure Linum populations and (2) the impact of an aggressive species ( Silene ) on co-occurring less aggressive species ( Linum ) becomes more severe under elevated CO₂ as a result of amplified interspecific root competition.     

More Ornamented Males Exhibit Increased Predation Risk and Antipredatory Escapes,but not Greater Mortality

Secondary sexual traits not only confer benefits to their bearer through increased mate acquisition, but may also have inherent costs, including the attraction of predators. Here, we examined the relationship between conspicuous secondary sexual traits and predation costs using two male morphs of Schizocosa wolf spiders: brush‐legged and non‐ornamented. In the field, we ran two predation experiments using artificial enclosures to directly test mortality costs of predation on the two male morphs. Using a natural predator, a larger wolf spider in the genus Hogna, we found no difference in predation on brush‐legged vs. non‐ornamented males. However, predation was depends on environmental conditions. More individuals were preyed upon at night (vs. during the day) and on rock litter (vs. leaf litter), but the two male morphs were preyed upon equally to each other across environmental treatments. A laboratory experiment incorporated staged interactions between a single predator (Hogna) and each male morph to examine finer details of predation events. Again, we found no differential mortality between brush‐legged and non‐ornamented males. However, brush‐legged males were attacked sooner and were more likely to escape the attack. Our results show an association between sexual ornamentation and predation risk as well as escape behavior.     

Negative Correlation between Ant and Spider Abundances in the Canopy of a Bornean Tropical Rain Forest

In tropical rain forests, high canopy trees have diverse and abundant populations of ants and spiders. However, accessing high trees and their fauna remains difficult; thus, how ants and spiders interact in the canopy remains unclear. To better understand the interspecific interactions between these two dominant arthropod groups, we investigated their spatial distributions at the canopy surface in a tropical rain forest in Borneo. We sampled ants and spiders six times between 2009 and 2011 by sweeping with an insect net at the tree crown surfaces of 190 emergent or tall (≥20 m in height) trees. We collected 438 ant individuals belonging to 94 species and 1850 spider individuals (1630 juveniles and 220 adults) belonging to 142 morphospecies (adults only) from a total of 976 samples. The fact that we collected four times more spider individuals than ant individuals suggests that fewer ants forage at the tree crown surface than previously thought. The number of spider individuals negatively correlated with the number of ant individuals and the number of ant species, indicating significant exclusivity between ant and spider spatial distributions at the tree crown surface. Niche‐overlap between the two taxa confirmed this observation. Although our data do not address the causes of these spatial distributions, antagonistic interspecific interactions such as interference behaviors and intra‐guild predation are ecological mechanisms that give rise to exclusive spatial distributions.     

The energetics of mimicry: the cost of pedestrian transport in a formicine ant and its mimic, a clubionid spider

ABSTRACT. Little information exists on the energetics of locomotion in small insects, and none in small spiders. We examined standard rate of oxygen consumption (SO₂) and net cost of transport (NCOT) in Camponotus sericeiventris (Guerin), a formicine ant, Myrmecotypus rettenmeyeri (Unzicker), its clubionid spider mimic (mean masses 43 and 24 mg, respectively), and an unrelated clubionid, Clubiona barroana (Chickering), mean mass 37mg. All species are from Barro Colorado Island, Panama. NCOT in the species studied was 12, 21 and 27 ml O₂g^-1 km^-1, respectively; NCOT in the two spiders was significantly higher than in the ant. The minimum cost of transport of M. rettenmeyeri (8.6ml O₂g^-1 km^-1), though low, did not differ significantly from the value predicted for an insect of its body mass, while its Y intercept elevation (estimated O₂ at zero running speed/SO₂) was extremely high. Y intercept elevation may be high in spiders as a group, leading to high NCOT at low running speeds, and hence to a tendency to adopt ambush predation. It is also predicted that, to minimize locomotion cost per unit distance, spiders will travel faster than insects of equivalent body mass.     

Roles of endothermy in niche differentiation for ball-rolling dung beetles (Coleoptera: Scarabaeidae) along an altitudinal gradient

Abstract.  1. An analysis of whether niche differentiation in ball-rolling dung beetles can be explained by the way in which they regulate their body temperature was conducted.
2.  A priori assumptions were: (i) if thermoregulation affects niche partitioning, sympatric species must have different endothermic strategies that minimise encounters; or, alternatively (ii) if two co-occurring species show the same thermoregulation pattern and their flight periods overlap, they might be avoiding competition by exhibiting different resource preferences or different food relocation behaviour.
3. The ball-rolling dung beetles studied showed a hierarchical structure based on the species' endothermic capacity, measured as temperature excess [ T _ex= difference between body temperature ( T _b) and ambient temperature ( T _a)]. Those with a high T _ex (10–15 °C) were located exclusively at altitudes >1000 m a.s.l. On the coastal plains, species with a high T _ex were restricted to flying at night when the T _a was lower. Species with a lower T _ex (less than 10 °C higher than T _a) were found in the coastal plains zone.
4. Where there was sympatry with similar trophic habits, the species involved showed very different thermal niches, and where there was significant overlap of thermal niches between sympatric species, trophic habits of species were very different.
5. The results suggest that it is possible to use the concept of the thermal niche as a tool to explain interspecific interactions and the spatial distribution of species.     

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.