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.     

Plant–animal interactions between carnivorous plants,sheet‐web spiders,and ground‐running spiders as guild predators in a wet meadow community

1. Plant–animal interactions are diverse and widespread shaping ecology, evolution, and biodiversity of most ecological communities. Carnivorous plants are unusual in that they can be simultaneously engaged with animals in multiple mutualistic and antagonistic interactions including reversed plant–animal interactions where they are the predator. Competition with animals is a potential antagonistic plant–animal interaction unique to carnivorous plants when they and animal predators consume the same prey.
2. The goal of this field study was to test the hypothesis that under natural conditions, sundews and spiders are predators consuming the same prey thus creating an environment where interkingdom competition can occur.
3. Over 12 months, we collected data on 15 dates in the only protected Highland Rim Wet Meadow Ecosystem in Kentucky where sundews, sheet‐web spiders, and ground‐running spiders co‐exist. One each sampling day, we attempted to locate fifteen sites with: (a) both sheet‐web spiders and sundews; (b) sundews only; and (c) where neither occurred. Sticky traps were set at each of these sites to determine prey (springtails) activity–density. Ground‐running spiders were collected on sampling days. DNA extraction was performed on all spiders to determine which individuals had eaten springtails and comparing this to the density of sundews where the spiders were captured.
4. Sundews and spiders consumed springtails. Springtail activity–densities were lower, the higher the density of sundews. Both sheet‐web and ground‐running spiders were found less often where sundew densities were high. Sheet‐web size was smaller where sundew densities were high.
5. The results of this study suggest that asymmetrical exploitative competition occurs between sundews and spiders. Sundews appear to have a greater negative impact on spiders, where spiders probably have little impact on sundews. In this example of interkingdom competition where the asymmetry should be most extreme, amensalism where one competitor experiences no cost of interaction may be occurring.

     

Species abundance patterns of coccinellid communities associated with olive,chestnut and almond crops in north‐eastern Portugal

• 1 The patterns of abundance of coccinellid species associated to the main agricultural tree crops of north‐eastern Portugal namely olive, chestnut and almond were studied.
• 2 During three to four crop seasons, eight olive, five chestnut and one almond groves were sampled. In each grove, five samples were collected from 10 randomly selected trees using the beating technique and the coccinellids were counted and identified to species. Principal component analysis was used to establish associations among crop and coccinellid species.
• 3 The mean species richness was higher in chestnut, with 15 ± 3.81 species/grove, followed by olive and almond, with 13 ± 2.76 and 10 ± 2.97 species/grove, respectively. Scymnus mediterraneus was the most abundant species in olive and almond, whereas Scymnus interruptus was dominant in chestnut. Brumus quadripustulatus, Chilocorus bipustulatus, Scymnus subvillosus, S. mediterraneus and Rhyzobius chrysomeloides were associated with olive, whereas S. interruptus, Coccinella septempunctata and Adalia decempunctata were associated with chestnut and Hippodamia variegata, Oenopia conglobata and Adalia bipunctata with almond. Both Stethorus punctillum and Scymnus apetzi species were similarly associated with chestnut and almond.
• 4 The differences in coccinellid communities could have been related to the kind of prey item present in the different trees. This knowledge can be used to develop integrated pest management programmes that encourage greater natural enemy biodiversity in agroecosystems.

     

Characterization of wild bee communities in apple and blueberry orchards

1. Wild bees provide invaluable ecosystem services in agricultural landscapes such as pollination. However, in recent decades, pollinator biodiversity, especially in wild bees, is declining on a global scale, with potentially far‐reaching consequences for crop production. Thus, there is an urgent need to determine whether wild bees are present in agricultural systems, such as fruit orchards.
2. In the present study, we examined the wild bee fauna at species and community levels during the period of bee activity (May to August) in apple and high‐bush blueberry orchards in New England.
3. Bee communities are crop‐specific and dominated by very few species, which fluctuate according to crop and season. The blueberry associated bee fauna was more diverse. In apple, communities were phylogenetically clustered at the genus level and dominated by solitary ground nesting bees within the genus Andrena. Species fluctuated widely in presence and abundance throughout the season, leading to differences in community composition and functional trait structure.
4. The results obtained in the present study show that apple and blueberry harbour a distinct and diverse bee fauna that performs vital pollination services in orchards. Our results provide essential baseline data for wild bees in blueberry and apple orchards and this can be used to improve management and conservation strategies for wild bee preservation in these crops.

     

Predation by generalist predators on the codling moth versus a closely‐related emerging pest the oriental fruit moth: a molecular analysis

• 1 Biological control by conservation of native natural enemies can, at its best, reduce the need for pesticides and prevent detrimental effects upon the environment. The present study investigated the role of ground‐active generalist predators as natural enemies of two tortricid pests in apple orchards.
• 2 Predation rates were compared on the well established codling moth Cydia pomonella and the emerging oriental fruit moth Grapholita molesta, which has recently switched hosts to apples.
• 3 The present study hypothesized that the ground‐active predators consumed the two tortricid pests in significant numbers without preference, and attacked the pests at different developmental stages.
• 4 Using diagnostic polymerase chain reaction on the gut contents of field‐caught ground‐active predators, no difference in predation rates was found on these two pests. Spiders were the most efficient predators of emergent adult moths in spring, whereas the carabid beetles, feeding on diapausing larvae, were important in the autumn.
• 5 The temporal complementarity between spiders and carabid beetles, attacking different stages of the pests at different times of year, highlights the need for diverse predator assemblages to optimize biological control.

     

Functional responses of three guilds of spiders: Comparing single‐ and multiprey approaches

Spiders are successful natural enemies of pests occurring throughout the different strata of an agroecosystem. The study of their functional responses can provide information related to the potential effectiveness of different species and guilds on reducing a pest population. However, multiple prey availability may change the functional response of a predator. In this study, the functional responses of three species of spiders in single‐prey and multiple‐prey experiments were modelled. The spider species Haplodrassus rufipes, Araniella cucurbitina and Synema globosum were chosen as being representatives of ground runners, orb‐weavers and ambushers, respectively. Three prey species were selected: a target prey, the Mediterranean fruit fly Ceratitis capitata and two alternate prey species, the flour moth Ephestia kuehniella and the house cricket Acheta domesticus. When the selected target prey C. capitata was supplied in the single‐prey experiments, the most and the least efficient spider species were H. rufipes and S. globosum, respectively. However, opposite results were obtained when alternative preys were supplied. Also, A. cucurbitina significantly changed its functional response with the presence of alternative prey species. Considering the prey preference during the multiple‐prey experiments, A. domesticus, used as representative of a heavy, long‐sized and highly motile prey, was avoided whereas C. capitata, the target pest used as representative of light, small‐sized and moderately motile prey was preferred by the three species of spiders. Ephestia kuehniella, used as representative of light, medium‐sized and low motile prey was occasionally consumed. Each guild could include efficient predators against pests according to its hunting strategies and the ecological exploited niches. Orb‐weavers could be efficient predators against flying pests; ambushers such as S. globosum could contribute to the reduction of the populations of flower‐visiting pests, whereas active ground hunters may also play an important role preying on pests that develop a part or all of its life cycle in the ground. However, further research on feeding behaviour such as prey switching is needed for a better understanding of the effectiveness of spiders as natural enemies.     

Rethinking trophic niches: Speed and body mass colimit prey space of mammalian predators

1. Realized trophic niches of predators are often characterized along a one‐dimensional range in predator–prey body mass ratios. This prey range is constrained by an “energy limit” and a “subdue limit” toward small and large prey, respectively. Besides these body mass ratios, maximum speed is an additional key component in most predator–prey interactions.
2. Here, we extend the concept of a one‐dimensional prey range to a two‐dimensional prey space by incorporating a hump‐shaped speed‐body mass relation. This new “speed limit” additionally constrains trophic niches of predators toward fast prey.
3. To test this concept of two‐dimensional prey spaces for different hunting strategies (pursuit, group, and ambush predation), we synthesized data on 63 terrestrial mammalian predator–prey interactions, their body masses, and maximum speeds.
4. We found that pursuit predators hunt smaller and slower prey, whereas group hunters focus on larger but mostly slower prey and ambushers are more flexible. Group hunters and ambushers have evolved different strategies to occupy a similar trophic niche that avoids competition with pursuit predators. Moreover, our concept suggests energetic optima of these hunting strategies along a body mass axis and thereby provides mechanistic explanations for why there are no small group hunters (referred to as “micro‐lions”) or mega‐carnivores (referred to as “mega‐cheetahs”).
5. Our results demonstrate that advancing the concept of prey ranges to prey spaces by adding the new dimension of speed will foster a new and mechanistic understanding of predator trophic niches and improve our predictions of predator–prey interactions, food web structure, and ecosystem functions.

     

Exploring the effect of soil management intensity on taxonomic and functional diversity of ants in Mediterranean olive groves

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Mass windborne migrations extend the range of the migratory locust in East China

1. Migratory insect pests pose a substantial challenge to global food security. These issues are particularly acute when pest incursions occur considerably beyond the expected range, through natural migration or human‐aided transport, because the lack of species‐specific control strategies and a potential absence of species‐specific natural enemies in the newly‐invaded area may lead to rapid establishment of a new pest.
2. One such threat is posed by the Oriental migratory locust Locusta migratoria manilensis in China, which, historically, has been restricted to eastern China from the Bohai Gulf southwards, and now threatens to expand its range into the agriculturally important region of northeast China.
3. We analyzed data from a recent outbreak of migratory locusts in Heilongjiang Province (extreme northeast China), > 700 km north of its current known range, and identified the source region, timing of arrival and probable migratory routes of this incursion.
4. We further show that warming temperatures in this region will likely allow subsequent invasions to establish permanent populations in northeast China, and thus authorities in this important crop‐producing region of East Asia should be vigilant to the threat posed by this species.

     

Influence of native ants on arthropod communities in a vineyard

• 1 Ants can have a range of effects on arthropods in crops, including suppressing herbivores such as caterpillars. However, ants can also increase hemipteran densities while reducing natural enemy numbers. In vineyard ecosystem, the effects of native ants and their interactions with other arthropods are poorly understood.
• 2 An ant‐exclusion experiment was designed to test the impact of native ants on both canopy and ground arthropods concurrently. The potential influence of ants on predation and parasitism of light brown apple moth (LBAM) eggs, a grape pest, was also examined. Adult grapevine scale insects and earwigs under bark were counted after a season of ant‐exclusion.
• 3 Among 23 ground ant species collected, six were found to forage in the canopy, with two Iridomyrmex species being the most commonly encountered.
• 4 There was no difference in the abundance of most arthropod orders and feeding groups between ant‐excluded and control vines, although ground spiders were more abundant under ant‐excluded vines, despite increased ground ant foraging pressure. LBAM egg parasitism and predation were low and probably affected by weather and other arthropods. Ant exclusion did not reduce survival of scale insects, although the distribution and abundance of scale insects were negatively associated with earwigs.
• 5 In conclusion, native ants did not consistently suppress arthropod assemblages, including natural enemies, and they did not promote the survival of scale insects. Interactions among native ant species within a vineyard might minimize their effects on other arthropods, although this needs further study.

     

Can natural enemies of current insect pests provide biotic resistance to future pests?

1. Economic pests jeopardize agricultural production worldwide. Classical biological control, comprising the import of exotic natural enemies to control target pest populations, has a successful history in many countries. However, little is known about how these natural enemies contribute to the suppression of pests that are yet to arrive. Biotic resistance theory, though, posits that communities resist species invasions as a result of natural enemies.
2. We assessed the potential of the resident exotic parasitoid wasp fauna in New Zealand (intentionally‐introduced biological control agents and unintentionally‐introduced species) to provide biotic resistance against possible future pests. A dataset was generated containing resident exotic parasitoid species (Ichneumonoidea: Braconidae; Ichneumonidae) in New Zealand, as well as their known global host ranges and the pest status of host species, to infer the potential for biotic resistance.
3. The known exotic ichneumonoid fauna in New Zealand comprises 65 species. These species associate with 107 host species in New Zealand, of which 54 species are pests. However, the current exotic species could potentially suppress 442 pest species not yet occurring in New Zealand.
4. This approach could be used to inform pest management programmes worldwide. Future research should consider how biotic resistance from the established parasitoid fauna can be used to inform specific decisions with respect to classical biological control.

     

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.     

Different groups of ground-dwelling spiders share similar trophic niches in temperate forests

1. Generalistic interactions between predator and prey may vary with ecosystem type, predator traits, and prey traits, but the interplay of these factors has not been assessed in ground food webs.
2. We investigated trophic interactions of ground-dwelling spiders across eight forests in European Russia associated with body size, hunting strategy, microhabitat specialization, potential prey type, potential prey population density, and forest type (coniferous vs. broadleaved). We analyzed 128 individual spiders, including juveniles, all identified to the family level with two complementary methods: molecular gut content analysis, and stable isotope analysis of carbon and nitrogen.
3. The results suggest that feeding frequency of spiders is affected by predator body size and by selection of certain prey type. Stable isotope analysis showed similar trophic niches among spider families, varying moderately with forest type. Larger spiders had higher Δ¹³C values than smaller ones, but similar Δ¹⁵N values, suggesting that different size classes of spiders belong to different food chains. Results based on stable isotope and molecular gut content analyses were weakly linked, indicating them targeting different trophic niche dimensions.
4. At least for the group-level interactions, family identity and hunting strategy of predator has little predictive power while predator body size and prey traits affected trophic niche dimensions calling for future studies in this direction. Large spiders feed more and rely on different basal resources than small spiders, suggesting that including small species and juveniles provides a more comprehensive picture of food web organization.

     

Modelling the effects of field spatial scale and natural enemy colonization behaviour on pest suppression in diversified agroecosystems

1. Diversifying agroecosystems by establishing or retaining natural vegetation in and around crop areas has long been recognized as a potentially effective means of bolstering pest control as a result of attracting more numerous and diverse natural enemies, although outcomes are inconsistent across species.
2. Little is known about the underlying mechanisms driving such differences in species responses, creating challenges for determining how best to manage landscapes for maximizing environmental services such as biological control.
3. The present study addresses gaps in our understanding of the link between noncrop vegetation in field margins and pest suppression by using a system of partial differential equations to model population‐level predator–prey interactions, as well as spatial processes, aiming to capture the dynamics of crop plants, herbivores and two generalist predators.
4. We focus on differences in how two predators (a carabid and a ladybird beetle) colonize crop fields where they forage for prey, examining differences in how they move into the fields from adjacent vegetation as a potential driver of differences in overall pest suppression.
5. The results obtained demonstrate that predator colonization behaviour and spatial scale are important factors with respect to determining the effectiveness of biological control.

     

Low metabolic rates in primitive hunters and weaver spiders

The rates of oxygen consumption and carbon dioxide release of primitive hunters and weaver spiders, the Chilean Recluse spider Loxosceles laeta Nicolet (Araneae: Sicariidae) and the Chilean Tiger spider Scytodes globula Nicolet (Araneae: Scytodidae), are analyzed, and their relationship with body mass is studied. The results are compared with the metabolic data available for other spiders. A low metabolic rate is found both for these two species and other primitive hunters and weavers, such as spiders of the families Dysderidae and Plectreuridae. The metabolic rate of this group is lower than in nonprimitive spiders, such as the orb weavers (Araneae: Araneidae). The results reject the proposition of a general relationship for metabolic rate for all land arthropods (related to body mass) and agree with the hypothesis that metabolic rates are affected not only by sex, reproductive and developmental status, but also by ecology and life style, recognizing here, at least in the araneomorph spiders, a group having low metabolism, comprising the primitive hunters and weaver spiders, and another group comprising the higher metabolic rate web building spiders (e.g. orb weavers).     

Trophic structure of the spider community of a Mediterranean citrus grove: A stable isotope analysis

Spiders are dominant terrestrial predators that consume a large variety of prey and engage in intraguild predation. Although the feeding habits of certain species are well known, the trophic structure of spider assemblages still needs to be investigated. Stable isotope analysis enables characterisation of trophic relationships between organisms because it tracks the energy flow in food webs and indicates the average number of trophic transfers between a given species and the base of the web, thus being a useful tool to estimate the magnitude of intraguild predation in food webs. Using this technique, we studied the trophic groups of spiders and their links within the arthropod food web of a Mediterranean organic citrus grove. We assessed the trophic positions of the 25 most common spider species relative to other arthropod predators and potential prey in the four seasons of the year, both in the canopy and on the ground. The analyses showed great seasonal variation in the isotopic signatures of some arthropod species, as well as the existence of various trophic groups and a wide range of trophic levels among spiders, even in species belonging to the same family. Differences in δ¹⁵N between spiders and the most abundant prey in the grove usually spanned two trophic levels or more. Our findings provide field evidence of widespread intraguild predation in the food web and caution against using spider families or guilds instead of individual species when studying spider trophic interactions.     

EcoPred: an educational individual based model to explain biological control,a case study within an arable land

ABSTRACT

Individual based models (IBMs) are up-to-date tools both in research and educational areas. Here we introduce an IBM built on NetLogo platform that simulates a top-down trophic cascade controlled by the pressure exerted by two model predators (web-building spiders and ground runner spiders) on a model pest (the olive fruit fly) within a hypothetical agricultural landscape (the olive crop). EcoPred is an IBM that aims to be an educational tool that can help teachers to explain concepts related to ecology in a modern, enjoyable and comprehensive way. EcoPred reflects the changes on a fly population within a simulated olive crop according to (1) the mortality rate caused by the predation of two spider species and energy loss, (2) the energy gain by feeding on flowers and (3) the reproduction rate in olive trees. The model was tested with 26 students achieving very good results in terms of acceptance and interest on the learning method. EcoPred can be used for educational purposes with 16 year old students and older to explain ecological concepts such as trophic level, species interactions, limiting factor and biological control in an interactive way simultaneously introducing students to biology oriented programming languages.     

Parasitoid genus‐specific manipulation of orb‐web host spiders (Araneae,Araneidae)

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The effect of femel- and small scale clear-cutting on ground dwelling spider communities in a Norway spruce forest in Southern Germany

The early effects of femel-cutting (removing 20% of the trees) and small scale clear-cutting on ground-living spiders in a Norway spruce (Picea abies (L.) Karst.) forest in Southern Germany were investigated. The study was carried out as BACIP (before and after, control-impact, many paired samplings) study: Spiders were sampled during the pre-treatment year, the year of cutting, and the year after cutting. In total 7101 individuals were sampled, of which 4530 individuals were identified, 4468 were adult and 2633 individuals were juvenile. We identified 107 species, but a single species, Coelotes terrestris, dominated the control (spruce stand) comprising up to 49% of the total identified individuals. Clear-cutting changed the species composition in the traps, while the first step in femel-cutting preserved it. The number of individuals of the families Linyphiidae, Amaurobiidae, Agelenidae and Clubionidae decreased drastically within the 2 years after the clear-cutting, while the Lycosidae became numerically dominant in the clear-cut stands. The number of individuals with the following characterisation decreased significantly after clear-cutting: Small (<3.0 mm) and large spiders (>10.5 mm), web builders, ‘forest habitat species’, species favouring hygrophilic to medium moisture conditions, and preferences to live below ground or in and on the moss layer. On the other hand, middle-sized spiders, free hunters, ‘open habitat species’, spiders favouring dry conditions or that are euryoecious, preferring patterns covered by grasses or uncovered patches, increased in number. Clear-cut habitats with dense spruce regeneration showed a delayed and less pronounced response. With femel-cutting, species composition of ground-living spider communities may be preserved during the first step of regeneration of mature forest stands.     

Body size determines the outcome of competition for webs among alien and native sheetweb spiders (Araneae: Linyphiidae)

Abstract 1. Biotic invasions are one of the most important reasons for changes in biodiversity. The alien sheetweb spider Mermessus trilobatus (Araneae: Linyphiidae) has become abundant in large parts of Central Europe within the past three decades. Its invasion might negatively influence native spiders, for instance via competition for webs. 2. Laboratory experiments were developed to test if M. trilobatus is competitively superior to native spiders. The alien M. trilobatus and five native sheetweb spiders (Erigone dentipalpis, E. atra, Gnathonarium dentatum, Dicymbium nigrum and Micrargus herbigradus) were compared with respect to their success to take over occupied webs from E. dentipalpis. 3. The rate of web takeover or defence was determined by body size, whereby individuals with a wider thorax invaded webs more successfully. After taking body size into account, the frequency of defence or web takeover did not differ between species. In 13% of all confrontations, predation against generally smaller opponents was recorded. Contrary to the predictions, raising the web value with food resources did not raise the effort expended on web defence but reduced predation by the web owner. 4. The current study does not indicate that the invasion of the relatively small‐sized M. trilobatus is facilitated by strong competitiveness. Nevertheless, M. trilobatus may displace smaller‐sized immature specimens and thereby threaten native spiders. Still, other reasons are likely to underlie the success of M. trilobatus in Europe, such as rapid reproduction or release from natural enemies.