Multitrophic Interactions Research Articles

Chewing up the Wood-Wide Web: Selective Grazing on Ectomycorrhizal Fungi by Collembola

The mycelia of some symbiotic ectomycorrhizal fungi form extensive networks—the so called “wood-wide web”—that have key roles in biogeochemical cycling. By interacting with myriad soil organisms such as collembola, the fungi directly affect the functioning of above- and below-ground multitrophic interactions in ecosystems. Here we tested whether the grazing activities of collembola affected the growth of ectomycorrhizal fungi in single or mixed species axenic cultures, and their impact on ectomycorrhizal diversity in litterbags in the field. We also used 14CO2 pulse-labelling to test the effects of collembola on respiratory losses of recent plant assimilate from external mycelium of ectomycorrhizal fungi in symbiosis with Scots pine or birch. We found that the effects of collembola varied across species, and caused a significant reduction in the amount of 14CO2 released from external mycorrhizal mycelium from three of the eight species combinations but increased it in one. Selective grazing also significantly affected the community structure of ectomycorrhizal fungi. Our findings demonstrate the importance of collembola in regulating ectomycorrhizal fungal diversity and activity and below-ground pathways of carbon flow.

Bird and bat predation services in tropical forests and agroforestry landscapes.

Understanding distribution patterns and multitrophic interactions is critical for managing bat- and bird-mediated ecosystem services such as the suppression of pest and non-pest arthropods. Despite the ecological and economic importance of bats and birds in tropical forests, agroforestry systems, and agricultural systems mixed with natural forest, a systematic review of their impact is still missing. A growing number of bird and bat exclosure experiments has improved our knowledge allowing new conclusions regarding their roles in food webs and associated ecosystem services. Here, we review the distribution patterns of insectivorous birds and bats, their local and landscape drivers, and their effects on trophic cascades in tropical ecosystems. We report that for birds but not bats community composition and relative importance of functional groups changes conspicuously from forests to habitats including both agricultural areas and forests, here termed 'forest-agri' habitats, with reduced representation of insectivores in the latter. In contrast to previous theory regarding trophic cascade strength, we find that birds and bats reduce the density and biomass of arthropods in the tropics with effect sizes similar to those in temperate and boreal communities. The relative importance of birds versus bats in regulating pest abundances varies with season, geography and management. Birds and bats may even suppress tropical arthropod outbreaks, although positive effects on plant growth are not always reported. As both bats and birds are major agents of pest suppression, a better understanding of the local and landscape factors driving the variability of their impact is needed.

Ecological turmoil in evolutionary dynamics of plant-insect interactions: defense to offence.

Available history manifests contemporary diversity that exists in plant-insect interactions. A radical thinking is necessary for developing strategies that can co-opt natural insect-plant mutualism, ecology and environmental safety for crop protection since current agricultural practices can reduce species richness and evenness. The global environmental changes, such as increased temperature, CO₂ and ozone levels, biological invasions, land-use change and habitat fragmentation together play a significant role in re-shaping the plant-insect multi-trophic interactions. Diverse natural products need to be studied and explored for their biological functions as insect pest control agents. In order to assure the success of an integrated pest management strategy, human activities need to be harmonized to minimize the global climate changes. Plant-insect interaction is one of the most primitive and co-evolved associations, often influenced by surrounding changes. In this review, we account the persistence and evolution of plant-insect interactions, with particular focus on the effect of climate change and human interference on these interactions. Plants and insects have been maintaining their existence through a mutual service-resource relationship while defending themselves. We provide a comprehensive catalog of various defense strategies employed by the plants and/or insects. Furthermore, several important factors such as accelerated diversification, imbalance in the mutualism, and chemical arms race between plants and insects as indirect consequences of human practices are highlighted. Inappropriate implementation of several modern agricultural practices has resulted in (i) endangered mutualisms, (ii) pest status and resistance in insects and (iii) ecological instability. Moreover, altered environmental conditions eventually triggered the resetting of plant-insect interactions. Hence, multitrophic approaches that can harmonize human activities and minimize their interference in native plant-insect interactions are needed to maintain natural balance between the existence of plants and insects.

A coat of many scents: Cuticular hydrocarbons in multitrophic interactions of fig wasps with ants

The fig–fig wasp system of Ficus racemosa constitutes an assemblage of galler and parasitoid wasps in which tritrophic interactions occur. Since predatory ants (Oecophylla smaragdina and Technomyrmex albipes) or mostly trophobiont-tending ants (Myrmicaria brunnea) were previously shown to differentially use volatile organic compounds (VOCs) from figs as proximal cues for predation on fig wasps, we examined the response of these ants to the cuticular hydrocarbons (CHCs) of the wasps. CHC signatures of gallers were distinguished from those of parasitoids by the methyl-branched alkanes 5-methylpentacosane and 13-methylnonacosane which characterised trophic group membership. CHC profiles of wasp predator and wasp prey were congruent suggesting that parasitoids acquire CHCs from their prey; the CHC composition of the parasitoid Apocrypta sp 2 clustered with that of its galler host Apocryptophagus fusca, while the CHC profile of the parasitoid Apocryptophagus agraensis clustered with its galler prey, the fig pollinator Ceratosolen fusciceps. In behavioural assays with ants, parasitoid CHC extracts evoked greater response in all ant species compared to galler extracts, suggesting that parasitoid CHC extracts contain more elicitors of ant behaviour than those of plant feeders. CHCs of some wasp species did not elicit significant responses even in predatory ants, suggesting chemical camouflage. Contrary to earlier studies which demonstrated that predatory ants learned to associate wasp prey with specific fig VOCs, prior exposure to fig wasp CHCs did not affect the reaction of any ant species to these CHCs.

Does vegetation complexity affect host plant chemistry, and thus multitrophic interactions, in a human-altered landscape?

Anthropogenic land use may shape vegetation composition and affect trophic interactions by altering concentrations of host plant metabolites. Here, we investigated the hypotheses that: (1) plant N and defensive secondary metabolite contents of the herb Plantago lanceolata are affected by land use intensity (LUI) and the surrounding vegetation composition (=plant species richness and P. lanceolata density), and that (2) changes in plant chemistry affect abundances of the herbivorous weevils Mecinus pascuorum and Mecinus labilis, as well as their larval parasitoid Mesopolobus incultus, in the field. We determined plant species richness, P. lanceolata density, and abundances of the herbivores and the parasitoid in 77 grassland plots differing in LUI index in three regions across Germany. We also measured the N and secondary metabolite [the iridoid glycosides (IGs) aucubin and catalpol] contents of P. lanceolata leaves. Mixed-model analysis revealed that: (1) concentrations of leaf IGs were positively correlated with plant species richness; leaf N content was positively correlated with the LUI index. Furthermore: (2) herbivore abundance was not related to IG concentrations, but correlated negatively with leaf N content. Parasitoid abundance correlated positively only with host abundance over the three regions. Structural equation models revealed a positive impact of IG concentrations on parasitoid abundance in one region. We conclude that changes in plant chemistry due to land use and/or vegetation composition may affect higher trophic levels and that the manifestation of these effects may depend on local biotic or abiotic features of the landscape.

Integrating more biological and ecological realism into studies of multitrophic interactions

Ecological EntomologyVolume 40, Issue 4 p. 349-352 Opinion Integrating more biological and ecological realism into studies of multitrophic interactions JEFFREY A. HARVEY, Corresponding Author JEFFREY A. HARVEY Department of Terrestrial Ecology, Netherlands Institute of Ecology, Wageningen, the Netherlands Section of Animal Ecology, Department of Ecological Sciences, VU University Amsterdam, Amsterdam, the NetherlandsCorrespondence: Jeffrey A. Harvey, Department of Terrestrial Ecology, Netherlands Institute of Ecology, Droevendaalsesteeg 10, 6708 PB Wageningen, the Netherlands. E-mail: [email protected]Search for more papers by this authorMIRIAMA MALCICKA, MIRIAMA MALCICKA Section of Animal Ecology, Department of Ecological Sciences, VU University Amsterdam, Amsterdam, the NetherlandsSearch for more papers by this authorJACINTHA ELLERS, JACINTHA ELLERS Section of Animal Ecology, Department of Ecological Sciences, VU University Amsterdam, Amsterdam, the NetherlandsSearch for more papers by this author JEFFREY A. HARVEY, Corresponding Author JEFFREY A. HARVEY Department of Terrestrial Ecology, Netherlands Institute of Ecology, Wageningen, the Netherlands Section of Animal Ecology, Department of Ecological Sciences, VU University Amsterdam, Amsterdam, the NetherlandsCorrespondence: Jeffrey A. Harvey, Department of Terrestrial Ecology, Netherlands Institute of Ecology, Droevendaalsesteeg 10, 6708 PB Wageningen, the Netherlands. E-mail: [email protected]Search for more papers by this authorMIRIAMA MALCICKA, MIRIAMA MALCICKA Section of Animal Ecology, Department of Ecological Sciences, VU University Amsterdam, Amsterdam, the NetherlandsSearch for more papers by this authorJACINTHA ELLERS, JACINTHA ELLERS Section of Animal Ecology, Department of Ecological Sciences, VU University Amsterdam, Amsterdam, the NetherlandsSearch for more papers by this author First published: 16 April 2015 https://doi.org/10.1111/een.12204Citations: 10Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Citing Literature Volume40, Issue4August 2015Pages 349-352 RelatedInformation

Host-microbe and microbe-microbe interactions in the evolution of obligate plant parasitism.

Research on obligate biotrophic plant parasites, which reproduce only on living hosts, has revealed a broad diversity of filamentous microbes that have independently acquired complex morphological structures, such as haustoria. Genome studies have also demonstrated a concerted loss of genes for metabolism and lytic enzymes, and gain of diversity of genes coding for effectors involved in host defense suppression. So far, these traits converge in all known obligate biotrophic parasites, but unexpected genome plasticity remains. This plasticity is manifested as transposable element (TE)-driven increases in genome size, observed to be associated with the diversification of virulence genes under selection pressure. Genome expansion could result from the governing of the pathogen response to ecological selection pressures, such as host or nutrient availability, or to microbial interactions, such as competition, hyperparasitism and beneficial cooperations. Expansion is balanced by alternating sexual and asexual cycles, as well as selfing and outcrossing, which operate to control transposon activity in populations. In turn, the prevalence of these balancing mechanisms seems to be correlated with external biotic factors, suggesting a complex, interconnected evolutionary network in host-pathogen-microbe interactions. Therefore, the next phase of obligate biotrophic pathogen research will need to uncover how this network, including multitrophic interactions, shapes the evolution and diversity of pathogens.

Current Research on Plant-Growth Promoting Rhizobacteria in Latin America: Meeting Report from the 2nd Latin American PGPR Workshop

Crop performance depends, to a large degree, on biological activities taking place in the root environment. By the early twentieth century, it was already recognized that plants exert key effects on the soil space just outside the root surface. This led to the concept of the rhizosphere, that is, the portion of the soil that is directly influenced by the root (Hiltner 1904). The rhizosphere contains diverse microorganisms that induce beneficial, neutral, or deleterious effects on plant growth. The beneficial rhizosphere bacteria were deemed plant-growth promoting rhizobacteria (PGPR) (Kloepper and Schroth 1978). The rhizosphere was then recognized to be an active microbial habitat with complex and multitrophic biological interactions among microbes and eukaryotic organisms, and focused studies on these interactions began. The applications of such knowledge were of direct economical relevance given that PGPRs may be utilized as agronomic inputs to increase crop yields. This gave rise to a community of scientists interested in elucidating the mechanisms displayed by PGPR species and understanding the role of the plant in shaping the microbial community of the rhizosphere. In parallel, a number of private companies started to commercialize PGPR-based products for a range of agronomical applications worldwide, with Latin American countries taking the lead in this field. With these interests in mind, the International PGPR Workshop was first held in Canada in 1987 and since then, the workshop has been held every 3 years at different locations around the world (Switzerland, Australia, Japan, Argentina, India, The Netherlands, USA and Colombia). With the selection of a Latin American venue for the last international PGPR workshop and based on a regional demand for exchange of basic and applied information about the biology of PGPR and its applications, Quirama (Medellin, Colombia) hosted the 1st official Latin American PGPR meeting as a branch of the International edition. At that time, it was decided that the Latin American PGPR would be held every two years, and that the next venue would be Argentina.

The arbuscular mycorrhiza fungusRhizophagus irregularisMUCL 41833 decreases disease severity of Black Sigatoka on banana c.v. Grande naine, underin vitroculture conditions

Introduction. Mycosphaerella fijiensis, the fungal pathogen causing Black Sigatoka disease, attacks almost all cultivars of bananas and plantains. Currently, the repeated application of fungicides is the most widespread control measure, while the use of bio-control agents remains almost ignored. Here we investigated, under in vitro culture conditions, whether an arbuscular mycorrhizal fungus (AMF – Rhizophagus irregularis MUCL 41833) could reduce the severity of disease caused by M. fijiensis MUCL 47740 on banana. Materials and methods. Prior to their transfer to autotrophic in vitro culture systems and subsequent inoculation by the pathogen, the banana plantlets cultivar Grande Naine (AAA genome Cavendish group) were grown in the extra-radical mycelium network of the AMF, arising from Medicago truncatula plantlets, for fungal root colonization. Results and discussion. At the time of infection with M. fijiensis, the AMF colonization of the banana plantlets was 12%, 56% and 10% for hyphae, arbuscules and spores/vesicles, respectively, and the number of spores produced in the medium was above 200. At day 21 and day 35 following infection by the pathogen, the number of extra-radical spores as well as the abundance of arbuscules in roots, were significantly higher than in the non-infected plantlets. Conversely, the severity index measured in the mycorrhizal plantlets decreased by more than 80% and 60%, respectively, 21 and 35 days after infection by the pathogen. Similarly, the area under disease progress curve, estimated at day 35, was reduced by 59% in the mycorrhizal banana plantlets as compared to the control plantlets. Whatever the treatment (mycorrhizal or non mycorrhizal plantlets in presence/absence of M. fijiensis), no significant differences were observed in plantlet dry weight, pseudostem height and diameter, and leaf area at both observation times. Conclusions. These results emphasize the complex multitrophic interactions between above and below-ground microorganisms mediated via the plant. They further suggest that AMF may decrease, at least at the early stage of infection, M. fijiensis symptoms possibly via the induction of a systemic resistance pathway. The important decrease in symptoms observed in the mycorrhizal banana plantlets suggest that these microorganisms may represent a potentially attractive option to consider in the context of an integrated control of this important disease.

Tritrophic interactions between parasitoids and cereal aphids are mediated by nitrogen fertilizer

Host plant nutritional quality can directly and indirectly affect the third trophic levels. The aphid-parasitoid relationship provides an ideal system to investigate tritrophic interactions (as the parasitoids are completely dependent for their development upon their hosts) and assess the bottom up forces operating at different concentrations of nitrogen applications. The effects of varying nitrogen fertilizer on the performance of Aphidius colemani (V.) reared on Sitobion avenae (F.) and Aphidius rhopalosiphi (D.) reared on Rhopalosiphum padi (L.) were measured. Parasitism and percent emergence of parasitoids were positively affected by nitrogen fertilizer treatments while developmental duration (egg, larval, and pupal stages) was not affected by increasing nitrogen inputs. In males and females of both parasitoid species, adult longevity increased with the increasing nitrogen fertilizer. Hind tibia length and mummy weight of both parasitoid species increased with nitrogen fertilizer concentrations, as a result of larger aphids. This study showed that nitrogen application to the soil can have important consequences for aboveground multitrophic interactions.

Traditional and molecular detection methods reveal intense interguild competition and other multitrophic interactions associated with native entomopathogenic nematodes in Swiss tillage soils

Background and aims As part of a research consortium that explores ways to improve soil health, we study how entomopathogenic nematodes (EPNs) can be better exploited for the biological control of soil-dwelling insect pests in annual crops. Methods We evaluated how tillage might affect belowground interactions in two 30-year running Swiss field trials by combining traditional (insect bait) and molecular (novel real-time qPCR protocols) methods. Soil samples (April and October 2013) were evaluated for the presence and activity of EPN soil food web assemblage comprising 13 EPN species, six nematophagous fungi, one ectoparasitic bacterium, and the free-living nematodes (FLN) of the Acrobeloides group. Results Mortality of sentinel larvae, as well as qPCR analyses (for which we provide seven new primers/ probes sets) found only trace levels of six EPN species, dominated by heterorhabditids species. Analysis of nematode progeny revealed that EPN compete intensely with FLN for insect cadavers. Overall, it appears that temperate annual cropping systems provide poor environments for EPN and that tillage does not negatively affect the natural occurrence of EPN. Conclusions Natural occurrence of EPN in Swiss tillage soils was very low, and augmentation may be a promising strategy to improve the control of root pests of annual crops.

Secretory activity of extrafloral nectaries shaping multitrophic ant-plant-herbivore interactions in an arid environment

In this study, we evaluated the effects of the secretory activity of nectaries on multitrophic interactions involving ants and herbivores foraging on individuals of Prosopis laevigata (Fabaceae) located in the arid Tehuacan-Cuicatlán valley, Mexico. We observed that the secretory activity of nectaries of P. laevigata appeared to follow the predictions of the ‘Optimal Defense Theory’. Specifically, our results suggest that due to high temperature and low humidity during the day, nectaries were more active at night, precisely when herbivores and ants were more abundant. Moreover, protective ants were always more abundant in the apical zones of the branches where youngest leaves are most susceptible to attack by herbivores. We hypothesized that P. laevigata could be optimizing nectar secretion in order to allocate defenses to maximize their individual fitness. Our study contributes to our understanding of how Optimal Defense Theory could shape multitrophic interactions between ants, plants, and herbivores mediated by secretory activity of nectaries in arid environments.

Plant-insect interactions under bacterial influence: ecological implications and underlying mechanisms.

Plants and insects have been co-existing for more than 400 million years, leading to intimate and complex relationships. Throughout their own evolutionary history, plants and insects have also established intricate and very diverse relationships with microbial associates. Studies in recent years have revealed plant- or insect-associated microbes to be instrumental in plant-insect interactions, with important implications for plant defences and plant utilization by insects. Microbial communities associated with plants are rich in diversity, and their structure greatly differs between below- and above-ground levels. Microbial communities associated with insect herbivores generally present a lower diversity and can reside in different body parts of their hosts including bacteriocytes, haemolymph, gut, and salivary glands. Acquisition of microbial communities by vertical or horizontal transmission and possible genetic exchanges through lateral transfer could strongly impact on the host insect or plant fitness by conferring adaptations to new habitats. Recent developments in sequencing technologies and molecular tools have dramatically enhanced opportunities to characterize the microbial diversity associated with plants and insects and have unveiled some of the mechanisms by which symbionts modulate plant-insect interactions. Here, we focus on the diversity and ecological consequences of bacterial communities associated with plants and herbivorous insects. We also highlight the known mechanisms by which these microbes interfere with plant-insect interactions. Revealing such mechanisms in model systems under controlled environments but also in more natural ecological settings will help us to understand the evolution of complex multitrophic interactions in which plants, herbivorous insects, and micro-organisms are inserted.

Dietary specialization and the effects of plant species on potential multitrophic interactions of three species of nymphaline caterpillars

AbstractThe diet breadth of insect herbivores influences their response to variation in plant quality, and these bitrophic interactions have implications for the higher‐level trophic interactions between herbivores and their natural enemies. In this comparative study, we examined the role of host plant species and plant secondary chemistry on the potential interactions between three species of nymphaline caterpillars and their natural enemies. The caterpillar species (all Lepidoptera: Nymphalidae) varied in their degree of specialization: the buckeye, Junonia coenia Hübner, is a specialist on plants that contain iridoid glycosides (IGs); the white peacock, Anartia jatrophae L., feeds on plants in five families, some of which contain IGs and some of which do not; and the painted lady, Vanessa cardui L., is a generalist, feeding on plants in at least 15 families. Each species was reared on leaves of an introduced host plant, Plantago lanceolata L. (Plantaginaceae), which produces two IGs, aucubin and catalpol, and on another plant species that is a common host plant. These alternate host plants were Plantago major L. (Plantaginaceae) for J. coenia, Bacopa monnieri (L.) Pennell (Plantaginaceae) for A. jatrophae, and Malva parviflora L. (Malvaceae) for V. cardui. We examined growth, sequestration, and immune response of these caterpillars on the different host plant species. Junonia coenia developed more rapidly and sequestered higher IG concentrations when reared on P. lanceolata, whereas both other species grew more slowly on P. lanceolata. Host plant did not influence immune response of J. coenia or A. jatrophae, whereas V. cardui immune response was weaker when reared on P. lanceolata. Junonia coenia was most efficient at IG sequestration and A. jatrophae was least efficient, when all three species were reared on P. lanceolata. These results indicate that diet breadth may play an important role in structuring tritrophic interactions, and this role should be further explored.

Stable isotope labelling of earthworms can help deciphering belowground–aboveground interactions involving earthworms, mycorrhizal fungi, plants and aphids

Functional relationships between belowground detritivores and/or symbionts and aboveground primary producers and their herbivores are not well studied. In a factorial greenhouse experiment we studied interactions between earthworms (addition/no addition of Lumbricus terrestris; Clitellata: Lumbricidae) and arbuscular-mycorrhizal fungi (AMF; with/without inoculation of Glomus mosseae; Glomerales: Glomeraceae) on the leguminous herb Trifolium repens (Fabales: Fabaceae) and associated plant aphids (Aphis gossypii, A. craccivora; Hemiptera: Aphidoidea). In order to be able to trace organismic interactions, earthworms were dual-labelled with stable isotopes (15N-ammonium nitrate and 13C-glucose). We specifically wanted to investigate whether (i) isotopic signals can be traced from the labelled earthworms via surface castings, plant roots and leaves to plant aphids and (ii) these compartments differ in their incorporation of stable isotopes. Our results show that the tested organismic compartments differed significantly in their 15N isotope enrichments measured seven days after the introduction of earthworms. 15N isotope incorporation was highest in casts followed by earthworm tissue, roots and leaves, with lowest 15N signature in aphids. The 13C signal in roots, leaves and aphids was similar across all treatments and is for this reason not recommendable for tracing short-term interactions over multitrophic levels. AMF symbiosis affected stable isotope incorporation differently in different subsystems: the 15N isotope signature was higher below ground (in roots) but lower above ground (leaves and aphids) in AMF-inoculated mesocosms compared to AMF-free mesocosms (significant subsystem × AMF interaction). Aphid infestation was unaffected by AMF and/or earthworms. Generally, these results demonstrate that plants utilize nutrients excreted by earthworms and incorporate these nutrients into their roots, leaf tissue and phloem sap from where aphids suck. Hence, these results show that earthworms and plant aphids are functionally interlinked. Further, 15N-labelling earthworms may represent a promising tool to investigate nutrient uptake by plants and consequences for belowground-aboveground multitrophic interactions.

Enantiospecific responses of southern pine beetle (Dendroctonus frontalis) and its clerid predator, Thanasimus dubius, to α-pinene

Multi-trophic interactions between pine bark beetles, their host trees, and predators are mediated in part by volatile terpenes in host tree oleoresin that can influence aggregation and/or host finding by both prey and predator species. The southern pine beetle, Dendroctonus frontalis Zimmermann, mass-attacks pine trees in response to its aggregation pheromone combined with host resin odors including a-pinene. We investigated discrimination of a- pinene enantiomers in olfactory responses of D. frontalis, and in behavioral responses of D. frontalis and its major clerid predator, Thanasimus dubius (Fabricius). Trapping trials in the spring and fall assessed attraction of both species to the D. frontalis aggregation pheromone com- ponents, frontalin and endo-brevicomin, either alone or in combination with a-pinene lures of differing enantiomeric compositions. a-Pinene lures enriched with the (?)-enan- tiomer (97.5 %) increased D. frontalis catches significantly more than (-)-enriched (93 %) lures, but did not differ from racemic lures. Sexes of D. frontalis did not differ from one another in their responses to the enantiomers, and there was no difference in lure discrimination by D. fron- talis and T. dubius. Thanasimus dubius did not distinguish between different a-pinene enantiomers. Dose-response electroantennogram studies of D. frontalis indicated that their antennae had a slightly lower response threshold to (?) than (-)-a-pinene. Each enantiomer habituated the antennae more to itself than to its antipode, implying the existence of olfactory receptors with differing affinities for enantiomers. The preference of D. frontalis for (?)-a- pinene may affect its host selection behavior, and should be considered in population monitoring lures.

The effect of Chrysoperla carnea (Neuroptera: Chrysopidae) and Adalia bipunctata (Coleoptera: Coccinellidae) on the spread of cucumber mosaic virus (CMV) by Aphis gossypii (Hemiptera: Aphididae).

The effects of two aphidophagous predators, the larvae of Chrysoperla carnea and adults of Adalia bipunctata, on the spread of cucumber mosaic virus (CMV) transmitted in a non-persistent manner by the cotton aphid Aphis gossypii were studied under semi-field conditions. Natural enemies and aphids were released inside insect-proof cages (1 m × 1 m × 1 m) with a central CMV-infected cucumber plant surrounded by 48 healthy cucumber seedlings, and the spatiotemporal dynamics of the virus and vector were evaluated in the short and long term (1 and 5 days) in the presence and absence of the natural enemy. The spatial analysis by distance indices methodology together with other indices measuring the dispersal around a single focus was used to assess the spatial pattern and the degree of association between the virus and its vector. Both natural enemies significantly reduced the number of aphids in the CMV-source plant after 5 days but not after 1 day. The CMV transmission rate was generally low, especially after 1 day, due to the limited movement of aphids from the central CMV-source plant, which increased slightly after 5 days. Infected plants were mainly located around the central virus-infected source plant, and the percentage of aphid occupation and CMV-infected plants did not differ significantly in absence and presence of natural enemies. The distribution patterns of A. gossypii and CMV were only coincident close to the central plant. The complexity of multitrophic interactions and the role of aphid predators in the spread of CMV are discussed.

Identifying qualitative effects of different grazing types on below-ground communities and function in a long-term field experiment.

Herbivory is an important modulator of plant biodiversity and productivity in grasslands, but our understanding of herbivore-induced changes on below-ground processes and communities is limited. Using a long-term (17 years) experimental site, we evaluated impacts of rabbit and invertebrate grazers on some soil functions involved in carbon cycling, microbial diversity, structure and functional composition. Both rabbit and invertebrate grazing impacted soil functions and microbial community structure. All functional community measures (functions, biogeochemical cycling genes, network association between different taxa) were more strongly affected by invertebrate grazers than rabbits. Furthermore, our results suggest that exclusion of invertebrate grazers decreases both microbial biomass and abundance of genes associated with key biogeochemical cycles, and could thus have long-term consequences for ecosystem functions. The mechanism behind these impacts are likely to be driven by both direct effects of grazing altering the pattern of nutrient inputs and by indirect effects through changes in plant species composition. However, we could not entirely discount that the pesticide used to exclude invertebrates may have affected some microbial community measures. Nevertheless, our work illustrates that human activity that affects grazing intensity may affect ecosystem functioning and sustainability, as regulated by multi-trophic interactions between above- and below-ground communities.

Ecological interactions shape the dynamics of seed predation in Acrocomia aculeata (Arecaceae).

BackgroundThe complex network of direct and indirect relationships determines not only the species abundances but also the community characteristics such as diversity and stability. In this context, seed predation is a direct interaction that affects the reproductive success of the plant. For Acrocomia aculeata, the seed predation by Pachymerus cardo and Speciomerus revoili in post-dispersal may destroy more than 70% of the propagules and is influenced by the herbivory of the fruits during pre-dispersal. Fruits of plants with a higher level of herbivory during pre-dispersal are less attacked by predators in post-dispersal. We proposed a hypothesis that describes this interaction as an indirect defense mediated by fungi in a multitrophic interaction. As explanations, we proposed the predictions: i) injuries caused by herbivores in the fruits of A. aculeata favor fungal colonization and ii) the colonization of A. acuelata fruit by decomposing fungi reduces the selection of the egg-laying site by predator.Methodology/Principal FindingsFor prediction (i), differences in the fungal colonization in fruits with an intact or damaged epicarp were evaluated in fruits exposed in the field. For prediction (ii), we performed fruit observations in the field to determine the number of eggs of P. cardo and/or S. revoili per fruit and the amount of fungal colonization in the fruits. In another experiment, in the laboratory, we use P. cardo females in a triple-choice protocol. Each insect to choose one of the three options: healthy fruits, fruits with fungus, or an empty pot. The proposed hypothesis was corroborated. Fruits with injuries in the epicarp had a higher fungal colonization, and fruits colonized by fungi were less attractive for egg-laying by seed predators.Conclusion/SignificanceThis study emphasizes the importance of exploring the networks of interactions between multitrophic systems to understand the dynamics and maintenance of natural populations.

Human‐induced biotic invasions and changes in plankton interaction networks

Summary Pervasive and accelerating changes to ecosystems due to human activities remain major sources of uncertainty in predicting the structure and dynamics of ecological communities. Understanding which biotic interactions within natural multitrophic communities are weakened or augmented by invasions of non‐native species in the context of other environmental pressures is needed for effective management. We used multivariate autoregressive models with detailed time‐series data from largely freshwater and brackish regions of the upper San Francisco Estuary to assess the topology, direction and strength of trophic interactions following major invasions and establishment of non‐native zooplankton in the early 1990s. We simultaneously compared the effects of fish and clam predation, environmental temperature and salinity intrusion using time‐series data from >60 monitoring locations spanning more than three decades. We found changes in the networks of biotic interactions in both regions after the major zooplankton invasions. Our results imply an increased pressure on native herbivores; intensified negative interactions between herbivores and omnivores; and stronger bottom‐up influence of juvenile copepods but weaker influence of phytoplankton as a resource for higher trophic levels following the invasions. We identified salinity intrusion as a primary pressure but showed relatively stronger importance of biotic interactions for understanding the dynamics of entire communities. Synthesis and applications. Our findings highlight the dynamic nature of biotic interactions and provide evidence of how simultaneous invasions of exotic species may alter interaction networks in diverse natural ecosystems over large spatial and temporal scales. Efforts to restore declining fish stocks may be in vain without fully considering the trophic dynamics that limit the flow of energy to target populations. Focusing on multitrophic interactions that may be threatened by invasions rather than a limited focus on responses of individual species or diversity is likely to yield more effective management strategies.