Spider Presence Research Articles

Spider waste enhances soil nutrient content, soil respiration, and plant growth

Abstract Predators can alter the movement of nutrients through ecosystems by depositing waste products following predation. Whilst the benefits of predator waste for large predators (e.g. bears) or dense accumulations of predators (e.g. seabirds on islands) seem clear, less is known about whether smaller, solitary predators can have measurable effects on local ecosystem processes. In separate experiments with web‐building and wandering spiders, we tested if the presence of predators affected soil nutrient content, soil respiration, soil microbial communities, and plant growth. In the first experiment with black widow spiders, total nitrogen and nitrate were not affected by spider presence, but ammonia and phosphorus were higher from soil under the edge of the spider web than soil away from the spider. Soil respiration and plant growth were both higher in soil collected from under the spider retreat compared with soil collected away from the spider web. In a second experiment with wolf spiders, we tested for interactions between spiders and soil microbial communities. There were positive effects of wolf spider presence on all soil nutrients and there were interactions between spiders and soil type (i.e. field‐collected versus autoclaved) for total carbon, total nitrogen, nitrate, and pH. Spider presence and soil type also affected soil respiration and spider presence had a large effect on the composition of the microbial community of the soil. There were also positive effects of wolf spider presence on plant biomass and plant height, with a significant interaction between spiders and soil type for plant height. Overall, our results show that two spiders with different life histories (i.e. web‐building and wandering) both have significant positive effects on plant growth through the deposition of their waste products. These effects may occur through the direct deposition of nutrients and changes in soil microbial communities. Although, further work is needed to resolve these interactions. Read the free Plain Language Summary for this article on the Journal blog.

Phylogenetics and species delimitation of the recluse spider, Loxosceles rufescens (Araneae: Sicariidae) populations invading Bangkok, Thailand

The Mediterranean recluse spider, Loxosceles rufescens, has been discovered for the first time inhabiting human dwellings in Bangkok, Thailand. Expeditions across 39 localities revealed five establishments with L. rufescens populations. The highest density was recorded in a storage house on Yaowarat Road, located in the heart of Bangkok's Chinatown, where 315 individuals were found, including adults, juveniles, and spiderlings. This medically significant spider's presence in such a densely populated urban area raises concerns about potential envenomation risks. Thirteen specimens of L. rufescens were extracted for DNA and sequenced for molecular phylogenetic analyses. COI and ITS2 markers were used to investigate relationships within L. rufescens and across available Loxosceles species sequences. Results indicate COI is superior for resolving species-level genetic clusters compared to ITS2. Surprisingly, L. rufescens individuals from the same house were found in significantly distant COI lineages, suggesting mtDNA may not be suitable for studying intra-specific phylogeography in this case. Species delimitation methods ABGD and ASAP demonstrated promising results for both COI and ITS2, while bPTP and GMYC tended to overestimate species numbers. ITS2 exhibited high sequence similarity in L. rufescens, suggesting potential utility as a barcoding marker for identification of this globally distributed species. Genetic distance analyses revealed a potential barcoding gap (K2P) of 8–9 % for COI and <2 % for ITS2 in Loxosceles. This study contributes valuable sequence data for the medically important genus Loxosceles and highlights the need for integrative approaches in understanding its evolution and spread. The findings have important implications for pest management strategies and public health in urban environments.

Efecto de la presencia de la araña Peucetia viridans (Oxyopidae) en los visitantes florales y la producción de semillas de Cnidoscolus multilobus (Euphorbiaceae)

Estudiamos la interacción entre la planta Cnidoscolus multilobus, sus visitantes florales y la araña depredadora Peucetia viridans. La dieta de P. viridans estuvo compuesta exclusivamente por artrópodos (arañas 32%, insectos 68%). El tamaño del cuerpo de las presas fue de 5.9 ± 1.0 mm, y el ámbito de las presas fue de 11.0 ± 0.4 mm (i.e. 0.14-1.3 más grande que la araña). Basándonos en la frecuencia de alimentación y el tiempo disponible para capturar y alimentarse de las presas, una araña puede capturar hasta 3.9 presas por día, esto dependiendo de la época del año. Entre junio y octubre de 1998 probamos si el número de visitas a las flores era afectado por la presencia/ausencia de la araña (efecto visual). Probamos cuatro tratamientos: (1) sin araña, (2) con araña, (3) con araña modificada (carapacho pintado con rojo), y (4) araña falsa. Encontramos dos patrones dependiendo de la respuesta de los visitantes florales a la araña “invisible” (pintada y falsa). Estos patrones estaban cercanamente asociados con la abundancia de visitantes. Utilizando panículas cubiertas, estimamos el efecto de la presencia de las arañas sobre la producción de semillas. Durante los meses con menos abundancia de visitantes florales (junio, julio y octubre), las panículas sin arañas produjeron significativamente más semillas. Mientras que en agosto y septiembre, los meses con el mayor número de visitantes florales, no se encontraron diferencias significativas entre tratamientos. Los resultados sugieren que los visitantes florales pudieron evitar aquellas inflorescencias con arañas vivas visibles, pero no les fue posible reconocer a las arañas sin pintura. Ya que muchos visitantes florales son potenciales polinizadores, las arañas podrían indirectamente reducir el número de semillas en C. multilobus durante los meses cuando los visitantes florales eran menos abundantes y las arañas no estaban saciadas.

Ants Increase Cloverworm Herbivory Via Nonconsumptive Pathways

Generalist arthropod predators often exhibit a range of intraguild interactions reducing their potential efficacy as biological control agents. These interactions may include consumptive or nonconsumptive effects that mediate the impacts of herbivores. We examined interactions among 2 generalist predators, the striped lynx spider (Oxyopes salticus Hentz; Araneae: Oxyopidae) and an ant (Lasius neoniger Emery; Hymenoptera: Formicidae), and a herbivore, the green cloverworm (Hypena scabra F.; Lepidoptera: Erebidae), all prevalent in central Kentucky soybean agroecosystems. We hypothesized that individual predator treatments would reduce green cloverworm survival and resultant leaf damage, but that predators would interfere with each other when both were present. To study these interactions, field cages containing potted soybeans were used to examine 8 treatment combinations (control, cloverworm, spider, ant, spider + cloverworm, ant + cloverworm, ant + spider, and ant + spider + cloverworm). When proportional leaf damage was compared, spider, ant + spider, and spider + cloverworm treatments had significantly less damage than the ant, ant + cloverworm, and ant + spider + cloverworm treatments. Spider presence tended to decrease plant damage while ant presence significantly increased damage. No differences among treatments were found for either spider or cloverworm recovery, indicating potential nonconsumptive effects of ants that may include compensatory feeding. We found that generalist predators, such as L. neoniger, can inhibit biological control due to nonconsumptive interactions even when the same species in a different system provides substantial levels of pest suppression. Resumen Los depredadores de artropodos generalistas a menudo exhiben un rango de interacciones intra-gremial (entre el grupo depredador) reduciendo su eficacia potencial como agentes de control biologico. Estas interacciones pueden incluir efectos consuntivos o no consuntivos que median los impactos de los herbivoros. Examinamos las interacciones entre dos depredadores generalistas, la arana lince rayada (Oxyopes salticus Hentz; Araneae: Oxyopidae) y una hormiga (Lasius neoniger Emery; Hymenoptera: Formicidae), y un herbivoro, el gusano verde de trebol (Hypena scabra F.; Lepidoptera: Erebidae), todos prevalentes en los agroecosistemas de soja del centro del estado de Kentucky. Presumimos que los tratamientos de depredadores individuales reducirian la sobrevivencia del gusano verde de trebol y el dano resultante en las hojas, pero que los depredadores interferirian entre si cuando ambos estuvieran presentes. Para estudiar estas interacciones, se utilizaron jaulas de campo que contenian soja en maceta para examinar 8 combinaciones de tratamiento (el control, el gusano verde de trebol, arana, hormiga, arana + el gusano verde de trebol, hormiga + el gusano verde de trebol, hormiga + arana, y hormiga + arana + el gusano verde de trebol). Cuando se comparo el dano proporcional de las hojas, los tratamientos de arana, hormiga + arana y arana + el gusano verde de trebol tuvieron un dano significativamente menor que los tratamientos de hormiga, hormiga + el gusano verde de trebol y hormiga + arana + el gusano verde de trebol. La presencia de las aranas tiende a disminuir el dano a las plantas, mientras que la presencia de las hormigas aumenta significativamente el dano. No se encontraron diferencias entre los tratamientos para la recuperacion de la arana o el gusano verde de trebol, lo que indica posibles efectos no consuntivos de las hormigas que pueden incluir la alimentacion compensatoria. Descubrimos que los depredadores generalistas, como L. neoniger, pueden inhibir el control biologico debido a interacciones no consumidoras, incluso cuando la misma especie en un sistema diferente proporciona niveles sustanciales de supresion de plagas. Key Words: Hypena scabra; field cage; food web; Lasius neoniger; Oxyopes salticus View this article in BioOne

Antiherbivore protection and plant selection by the lynx spider Peucetia flava (Araneae: Oxyopidae) in the Brazilian Cerrado

AbstractSpiders are ubiquitous in most vegetation, however very little empirical data are available on specific spider–plant interactions and their reciprocal outcomes. In the Brazilian Cerrado, the plant Mimosa setosa var. paludosa, (Fabaceae) has glandular trichomes in its leaves and stems, commonly entrapping insects (i.e. carrion) as well as hosting the lynx spider, Peucetia flava. We hypothesized that: (1) the damage inflicted by exophytic (leaves) and endophytic (seeds) herbivore insects that overcome the glandular trichomes is lower in plants where the lynx spider is present; and (2) the presence of this predator is positively related to food availability (live insects and/or carrion) and plant size. We performed field observations and an experimental field study in terms of the spider's presence versus absence on the Fabaceae plants. Our results showed that the proportion of damaged foliolules on the Fabaceae plants differed between the spiders‐present and spiders‐absent treatments, and that the absence of spiders led to a 3.3‐fold increase in the number of damaged foliolules. However, there was no significant difference in the proportion of seeds taken by endophytic herbivores from branches with and without spiders. We also found that the presence of Peucetia flava was positively related to the presence of entrapped carrion on plants, and that there was a positive and marginally significant effect of increasing abundance of the spiders on taller plants. The results of this study suggest that it is more common to find lynx spiders interacting with M. setosa var. paludosa in larger plants with higher carrion abundance (food source), and that P. flava and M. setosa var. paludosa interact in a facultative mutualism, in which plants provide entrapped carrion for spiders to feed on and possibly facilitate prey manipulation. In return, lynx spiders decrease the damage inflicted by exophytic, but not by endophytic herbivores. These results also contribute to a better understanding of which ecological factors may affect plant selection by lynx spiders and what the influence of this predator is on the structure of food webs in glandular plants.

Density mediates grasshopper performance in response to temperature manipulation and spider predation in tallgrass prairie.

Species interactions are often context-dependent, where outcomes require an understanding of influences among multiple biotic and abiotic factors. However, it remains unclear how abiotic factors such as temperature combine with important biotic factors such as density-dependent food limitation and predation to influence species interactions. Using a native grassland - grasshopper - wolf spider model food chain in tallgrass prairie, we conducted a manipulative field experiment to examine how predator-prey interactions respond to manipulations of temperature, grasshopper density, and food chain length. We find that grasshopper performance responses to temperature and predator treatments were density dependent. At high densities, grasshopper survival decreased with increased temperature when no spiders were present. When spiders were present, grasshopper survival was reduced, and this effect was strongest in the cooled treatment. In contrast, grasshopper survival did not vary significantly with spider presence or among temperature treatments at low grasshopper densities. Our results indicate that context-dependent species interactions are common and highlight the importance of understanding how and when key biotic and abiotic factors combine to influence species interactions.

Crab spiders (Thomisidae) attract insect flower‐visitors withoutUVsignalling

1. Crab spiders (Thomisidae) indirectly affect insect flower‐visitor and flowering plant interactions by consuming and altering the behaviour of insects.2. Although one expects insect flower‐visitors to avoid crab spiders actively, some crab spider species are known to attract flower‐visitors. Crab spiders may useUVsignalling to lure potential prey to the flowers they occupy.3. In the present study, a field experiment was conducted to examine the effects of crab spiders occupying three prairie plant species for the insect flower‐visitor community. Pollinating insects were significantly attracted to inflorescences with crab spiders compared to inflorescences without crab spiders for two plant species, and herbivorous insects were attracted to inflorescences with crab spiders for one of these plant species. The two flowering plant species with increased pollinator visitation showed increased seed weights for plants with crab spiders, indicating crab spider presence indirectly increased pollination.4. To test theUVsignalling hypothesis, inflorescences with crab spiders of one plant species were observed under both aUV‐blocking plastic and a clear plastic control. Contrary to our prediction, flower‐visitors were not more likely to land on inflorescences under the clear plastic; theUVsignalling hypothesis was not supported. Other unknown explanations underlie prey attraction to inflorescences with crab spiders.

The distribution of cave twilight‐zone spiders depends on microclimatic features and trophic supply

AbstractCaves are not closed systems. Trophic dynamics in these habitats are driven by resource availability, and species that move between cave and outdoor environments may play a major role in resource availability. Spiders are among the most abundant invertebrates in caves; however, very few studies have tested factors hypothesized to affect the distribution of spiders among caves, and it is not known whether the trophic features of caves play a role in determining the occurrence, abundance, or breeding success of spiders. We assessed the distribution of the cave‐dwelling orb‐weaver spider Meta menardi in Italy, in a Mediterranean and in a Pre‐alpine area during summer and winter. We analyzed the relationships between spider distribution and multiple cave features, describing both the abiotic and the biotic environment. Using visual encounter surveys, the detection probability of this species was high, indicating that this technique provides reliable information on spider distribution. In Mediterranean caves, spider presence was more likely in cold and wet caves with abundant dipterans. In Pre‐alpine caves, spider presence was more likely in deep caves with abundant dipterans. Dipteran abundance was the variable best explaining spider distribution when pooling all sampled caves. This study shows that adults of M. menardi do not occur randomly among caves, but select caves with specific features. Prey availability and abiotic features are major determinants of habitat suitability for cave spiders. The strong relationship between spider distribution and prey availability suggests that the distribution of these spiders might be an indicator of the resources available in the twilight zones of caves.

Predator-Prey Interactions are Context Dependent in a Grassland Plant-Grasshopper-Wolf Spider Food Chain.

Species interactions are often context dependent, where outcomes vary in response to one or more environmental factors. It remains unclear how abiotic conditions like temperature combine with biotic factors such as consumer density or food quality to affect resource availability or influence species interactions. Using the large grasshopper Melanoplus bivittatus (Say) and a common wolf spider [Rabidosa rabida (Walkenaer)], we conducted manipulative field experiments in tallgrass prairie to examine how spider-grasshopper interactions respond to manipulations of temperature, grasshopper density, and food quality. Grasshopper survival was density dependent, as were the effects of spider presence and food quality in context-dependent ways. In high grasshopper density treatments, predation resulted in increased grasshopper survival, likely as a result of reduced intraspecific competition in the presence of spiders. Spiders had no effect on grasshopper survival when grasshoppers were stocked at low densities. Effects of the experimental treatments were often interdependent so that effects were only observed when examined together with other treatments. The occurrence of trophic cascades was context dependent, where the effects of food quality and spider presence varied with temperature under high-density treatments. Temperature weakly affected the impact of spider presence on M. bivittatus survivorship when all treatments were considered simultaneously, but different context-dependent responses to spider presence and food quality were observed among the three temperature treatments under high-density conditions. Our results indicate that context-dependent species interactions are common and highlight the importance of understanding how key biotic and abiotic factors combine to influence species interactions.

A Tank Bromeliad Favors Spider Presence in a Neotropical Inundated Forest.

Tank bromeliads are good models for understanding how climate change may affect biotic associations. We studied the relationships between spiders, the epiphytic tank bromeliad, Aechmea bracteata, and its associated ants in an inundated forest in Quintana Roo, Mexico, during a drought period while, exceptionally, this forest was dry and then during the flooding that followed. We compared spider abundance and diversity between ‘Aechmea-areas’ and ‘control-areas’ of the same surface area. We recorded six spider families: the Dipluridae, Ctenidae, Salticidae, Araneidae, Tetragnathidae and Linyphiidae among which the funnel-web tarantula, Ischnothele caudata, the only Dipluridae noted, was the most abundant. During the drought period, the spiders were more numerous in the Aechmea-areas than in the control-areas, but they were not obligatorily associated with the Aechmea. During the subsequent flooding, the spiders were concentrated in the A. bracteata patches, particularly those sheltering an ant colony. Also, a kind of specificity existed between certain spider taxa and ant species, but varied between the drought period and subsequent flooding. We conclude that climatic events modulate the relationship between A. bracteata patches and their associated fauna. Tank bromeliads, previously considered only for their ecological importance in supplying food and water during drought, may also be considered refuges for spiders during flooding. More generally, tank bromeliads have an important role in preserving non-specialized fauna in inundated forests.

Competition between introduced and native spiders (Araneae: Linyphiidae)

The European sheet-web spider Linyphia triangularis (Araneae: Linyphiidae) has become established in Maine, where it often reaches very high densities. Two lines of evidence from previous work suggest that L. triangularis affects populations of the native linyphiid spider Frontinella communis. First, F. communis individuals are relatively scarce in both forest and coastal habitat where L. triangularis is common, but more common where L. triangularis is at low density. Second, in field experiments, F. communis species are less likely to settle in experimental plots when L. triangularis is present, and F. communis disappears from study plots when L. triangularis is introduced. Here we test two mechanisms that may underlie these patterns. First, we tested whether L. triangularis invades and usurps the webs of F. communis. When spiders were released onto webs of heterospecifics, L. triangularis was more likely to take over or share webs of F. communis than the reverse. We also observed natural takeovers of F. communis webs. Second, we explored the hypothesis that L. triangularis reduces prey availability for native species. We sampled flying prey in areas with L. triangularis and those where it had been removed, and found no effect of spider presence on measured prey density. We also found no effect of prey supplementation on web tenacity in F. communis, suggesting that F. communis movements are not highly dependent on prey availability. We conclude that web takeover is likely more important than prey reduction in driving negative effects of L. triangularis on F. communis.

Calling All Arachnophobic Entomologists: A Request for Information

199 e.g., having to approach one in a behavioral avoidance test (Vasey et al. 2012). Development of arachnophobia may be influenced by a specific negative event (which could range from merely being frightened by the unexpected appearance of a spider during a sensitive moment to having a strong reaction to a toxic bite); however, spider-phobes often report that they have always been phobic (Jones and Menzies 1995). In something of a paradoxical situation, a survey of members of the American Tarantula Society showed that 51% of the respondents at one point had a fear of spiders, but used exposure and education to lessen their anxieties (Kleinknecht 1982). A blatantly obvious statement is that entomologists work with insects. Intriguingly, over the decades of research involving spiders, I have encountered a number of entomological colleagues who are arachnophobic, ranging from mild dislike to extreme repellent reactions. Considering the great variety of morphologies that insects display, it seems paradoxical that an entomologist would have a different reaction to spiders than to other arthropods. Two mild examples known to me include entomology faculty: one professor admitted that spiders “creeped him out” and another warned his staff during field research to avoid specific areas because of spider presence. In an example of an extreme case, a former entomology colleague, who grew up in endemic brown recluse spider territory, was so successfully indoctrinated to fear spiders by her parents that she could not photocopy a spider-related chapter from her medical entomology textbook, and she nervously asked whether tarantulas might be active during her weekend entomology field trips to the desert. On another occasion, I opened a package mailed to me Calling All Arachnophobic Entomologists: A Request for Information

Predators mediate the effects of a fungal pathogen on prey: an experiment with grasshoppers, wolf spiders, and fungal pathogens

Abstract.1. Prey interact with multiple kinds of enemies such as predators, parasites, and pathogens. Interactions among enemies can alter prey dynamics but they are often studied separately.2. During the summers of 2005–2006, we conducted a field experiment to examine interactions among grasshoppers, spider predators, and a lethal fungal pathogen of grasshoppers. Grasshopper nymphs were stocked into field enclosures. Predation was manipulated by adding spiders to enclosures on day 1, day 5, or day 10 of the experiment, or no spiders were added. We monitored grasshopper survival and grasshopper mortality from fungal pathogens for 4 weeks.3. Fungal pathogens were abundant in 2005 but not in 2006, probably because of favourable weather conditions in 2005. When fungal pathogens were abundant, spider presence reduced grasshopper mortality from fungal pathogens, but only when spiders were present early in the experiment (added on day 1 or day 5).4. The outcome of predator–prey interactions varied between years, probably as a result of differences in pathogen prevalence. In 2005, spider presence reduced the number of deaths from the pathogen, leading to a slight trend of increased grasshopper density. However, in 2006, when pathogens were not an important source of mortality, spider predation was compensatory.

Cold Pressor Pain Reduces Phobic Fear But Fear Does Not Reduce Pain

Negative emotion has a variable effect on pain perception. This variability has been explained by the motivational priming hypothesis (MPH) which predicts that emotional stimuli generating low levels of arousal will facilitate pain, while stimuli generating high levels of arousal will inhibit pain. However, a study by Sneddon et al with rainbow trout discovers a relationship not found in the human literature, that fear-related behavior decreased in the presence of a nociceptive stimulus. The current experiment examined this possibility in humans. In Experiment 1, 30 healthy, female subjects with "at least a mild aversion to spiders" participated in 3 trials: 1 in which a Brazilian salmon pink tarantula was present; a second with the right hand immersed in a cold pressor; and a third with both the tarantula and the cold pressor present. Experiment 2 added distance as an extra variable to this methodology. In both experiments it was found that spider presence had no impact upon pain perception but spider fear was reduced by the cold pressor. There was no interaction between trial and either time or distance. These findings are novel in human subjects and not well accounted for by the MPH. We suggest that an explicitly evolutionary framework should be adopted, and that spider fear was reduced to facilitate escape from the more threatening cold-pressor experience. This study examined the relationship between pain and fear. Subjects with an aversion to spiders sat next to a tarantula with their right hand in iced water. Subjects reported reduced fear but no change in pain. Consequently, the authors reevaluate the Motivational Priming Hypothesis and emphasize evolutionarily determined threat values.

Relationship between Disgust and Memory Biases in Spider Fear

The literatures examining disgust's role in information processing biases and evidence for memory biases in anxiety disorders are both mixed, suggesting small or fragile effects. Thus, to maximize power and reliability, a mega-analytic approach was used to examine data across two studies to determine whether a memory bias for spider-relevant information exists under conditions when disgust is elevated and if the bias is specific to highly fearful individuals. Disgust was manipulated by having a large tarantula present or absent (at encoding and/or at recall) when individuals high (N=158) or low (N=108) in spider fear completed a free recall task. Results indicated that, as expected, the spider's presence was related to enhanced recall of spider information. However, this bias was driven by the presence of the spider during encoding only (as opposed to during recall), and high trait spider fear was not necessary for the memory bias to be expressed. Finally, there was a small effect for individual differences in trait and state disgust to predict spider recall, but this effect disappeared when anxiety was also included as a predictor, suggesting only a limited role for disgust in memory biases related to specific fears.

Excretion behavior of adult female crab spiders Misumena vatia (Araneae, Thomisidae)

Abstract Excreta potentially provide parasites or predators with information about the presence of hosts or prey; hence, vulnerable individuals experience strong selection to minimize danger from this source. Alternatively or additionally, excreta could alert potential prey to a spider's presence. Adult female crab spiders Misumena vatia (Clerck 1757) exhibited a strong reluctance to excrete when retained under tightly confined conditions. Only 5% of regularly fed individuals (1% of total observations) excreted over observation periods of as many as 50 days while confined in 7-dram vials (5 cm high, 3 cm diameter). Individuals retained large amounts of excreta during this time. However, when released upon vegetation over two-thirds of them excreted within 5 min, after moving to the distal end of a leaf or petal such that the excreta fell below them onto lower vegetation or the substrate. In the field they showed little tendency to excrete close to their hunting sites. The ability to retain excreta should ...

Spiders (Arachnida: Araneae) Associated with Seed Heads of Sarracenia purpurea (Sarraceniaceae) at Acadia National Park, Maine

Abstract We discovered that spiders use seed heads of Sarracenia purpurea (Northern Pitcher Plant) for moulting, nesting, and rearing of young. These associations represent only a few of the diverse interactions between spiders and pitcher plants. During July–August 2001 at Acadia National Park, seed heads (n = 301) of S. purpurea from four bog-heaths yielded spiders (n = 685) of four families (Theridiidae, Dictynidae, Clubionidae, Salticidae), 10 genera, and at least 11 species. Two additional spider families (Gnaphosidae, Thomisidae) were represented by cast exuviae. Jumping spiders (Salticidae) were the chief occupants, comprising 80.0% of species and 99.1% of individuals. The salticid Tutelina similis was the most common inhabitant, accounting for 63.8% of the overall spider fauna in these microhabitats. Spider foraging-guild presence favored hunters (99.7%) over web spinners; juveniles outnumbered adults almost 15 to 1, and females outnumbered males 43 to 1. Frequencies of spider webbing and retreats...

Beneficial effect of spider presence on seedling recruitment of the tropical rainforest tree Dipteryx oleifera (Fabaceae)

This research presents evidence showing that: (1) lower arthropod herbivory correlates with seedling survival, and (2) spider presence correlates with lower arthropod herbivory, seedling growth, and seedling survival of the tropical rainforest tree species Dipteryx oleifera in eastern Nicaragua. The study was conducted from January 2005 to January 2006 in a 6.37 ha permanent plot established in 2002. Seedling height, spider behavior and presence on seedlings, and percentage of leaf area lost due to arthropod herbivory were measured. Arthropod herbivory was assessed from digital photographs of each seedling within the permanent plot. Seedling fate was followed in order to determine its correlation with spider presence, initial seedling size, and arthropod herbivory. A GLM showed that seedling survival correlated negatively with lower levels of arthropod herbivory (<20%), while seedlings with higher levels of herbivore damage experienced mortalities close to 100%. Results from another GLM suggests that seedling mean height (aprox. 8 cm) would be increased by approximately 1.5 cm for each year that spiders were present on seedlings and would be decreased 0.75 cm in height for each percent unit of arthropod herbivory. We also report a trend toward lower arthropod herbivory in seedlings colonized by spiders with aggressive traits, presumably because more aggressive spiders better defended seedlings against herbivorous arthropods than less aggressive spiders.

Reduction of Visitation Rates by Honeybees (Apis mellifera) to Individual Inflorescences of Lavender (Lavandula stoechas) upon Removal of Coloured Accessory Bracts (Hymenoptera: Apidae)

[Article] Honeybees (Apis mellifera Linnaeus 1758) choosing between inflorescences of Lavandula stoechas appear to use a two-stage decision process based on different morphological criteria at each stage. The first stage, whether to closely inspect inflorescences, is based on display size. Lavandula inflorescences have large showy terminal bracts at the apex which increase the apparent display size. However, crab spiders often conceal themselves by closing the bracts around themselves using silk. Two manipulation experiments were carried out on the effects of the bracts on visitation rates to individual inflorescences. In the first, inflorescences from which bracts were removed received a reduced rate of inspection. In the second, inflorescences in which bracts were stuck together, mimicking the spider behaviour, experienced the same number of inspections as controls. Hence, the bracts did play a role in attracting honeybees to inflorescences, perhaps because a lack of bracts is usually seen only in very young or very old inflorescences, neither of which produce any nectar. However, honeybees did not avoid the closed bracts (assumed to provide an indirect cue of spider presence), probably because spiders often move between inflorescences, thus making closed bracts unreliable as a cue to predation risk.

Effects of altered precipitation and wolf spiders on the density and activity of forest-floor Collembola

Summary A 2×2 factorial field experiment was conducted in a deciduous forest to determine how changes in moisture and numbers of a common wolf spider, Schizocosa, affect Collembola abundance and activity. Each of four 4-m2 fenced, roofed plots was divided into eight 0.5-m2 fenced subplots, and each subplot was assigned a rainfall treatment (drought or high-rainfall) and a Schizocosa treatment (Schizocosa-removal or Schizocosa-addition). Water was sprayed on the high-rainfall subplots weekly from 7 August to 1 October 2003 at a rate of roughly 2× the long-term mean, while the drought subplots received no water. In order to increase the probability of uncovering possible effects of Schizocosa, predatory arthropods (Schizocosa, other spiders, and centipedes) were first removed from all subplots; Schizocosa-addition subplots were then stocked with five juvenile Schizocosa on 19 August, with additional Schizocosa added throughout the experiment. An index of relative Collembola activity was calculated by comparing the number captured in pitfall traps (activity-density) with absolute density (no./m2) measured by extracting Collembola from litter samples. Decreased moisture reduced overall Collembola density, but led to increased Collembola activity. This response to rainfall was exhibited by the families Entomobryidae, Tomoceridae, and Hypogastruridae. The presence of Schizocosa had no impact on overall Collembola density, nor did spider presence affect Collembola activity, with the possible exception of the Hypogastruridae, for which there was an interaction between rainfall and Schizocosa presence. Hypogastrurid Collembola were more active in the drought subplots and exhibited the same level of activity in the presence or absence of Schizocosa under drought conditions. However, in the high-rainfall treatment, the presence of Schizocosa increased hypogastrurid activity.