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1.
- As the Earth's climate continues to change, drought and insect population outbreaks are predicted to increase in many parts of the world. It is therefore important to understand how changes in such abiotic and biotic stressors might impact agroecosystems.
- The plant stress hypothesis predicts that, owing to physiological and biochemical changes, plants experiencing drought will be more susceptible to insect herbivory, which could have synergistic negative effects on plant performance. By contrast, the plant vigor hypothesis predicts that insects will preferentially feed on fast‐growing vigorous plants.
- These hypotheses were tested in a field experiment using 16 soybean (Glycine max (L.) Merr.) genotypes to determine: (i) the combined effects of drought and herbivory on plant performance; (ii) the impact of drought on soybean resistance to herbivores; and (iii) how genetically variable phenotypic traits in soybean correlate with these responses.
- It was found that drought had a greater effect on soybean performance than herbivory, and drought and herbivory did not interact to impact on any measure of plant performance. Drought caused decreased insect herbivory on average, suggesting that the plant vigor hypothesis is consistent with the effects of drought stress on soybean resistance to leaf‐chewing insect herbivores. This conclusion is further supported by genotypic correlations which show that plant growth rate is positively correlated with the amount of herbivory plants received.
- These results suggest that, although the effects of climate‐associated changes in drought and herbivory will have negative effects on soybean, these potential effects are quantifiable with simple experiments and can be mitigated through continued breeding of varieties that are tolerant and resistant to these abiotic and biotic stressors.
2.
Ivo Beyaert Monika Hilker 《Biological reviews of the Cambridge Philosophical Society》2014,89(1):68-81
Insect olfactory orientation along odour plumes has been studied intensively with respect to pheromonal communication, whereas little knowledge is available on how plant odour plumes (POPs) affect olfactory searching by an insect for its host plants. The primary objective of this review is to examine the role of POPs in the attraction of insects. First, we consider parameters of an odour source and the environment which determine the size, shape and structure of an odour plume, and we apply that knowledge to POPs. Second, we compare characteristics of insect pheromonal plumes and POPs. We propose a ‘POP concept’ for the olfactory orientation of insects to plants. We suggest that: (i) an insect recognises a POP by means of plant volatile components that are encountered in concentrations higher than a threshold detection limit and that occur in a qualitative and quantitative blend indicating a resource; (ii) perception of the fine structure of a POP enables an insect to distinguish a POP from an unspecific odorous background and other interfering plumes; and (iii) an insect can follow several POPs to their sources, and may leave the track of one POP and switch to another one if this conveys a signal with higher reliability or indicates a more suitable resource. The POP concept proposed here may be a useful tool for research in olfactory‐mediated plant–insect interactions. 相似文献
3.
Michael J. Stout 《Insect Science》2013,20(3):263-272
Applied research on host‐plant resistance to arthropod pests has been guided over the past 60 years by a framework originally developed by Reginald Painter in his 1951 book, Insect Resistance in Crop Plants. Painter divided the “phenomena” of resistance into three “mechanisms,” nonpreference (later renamed antixenosis), antibiosis, and tolerance. The weaknesses of this framework are discussed. In particular, this trichotomous framework does not encompass all known mechanisms of resistance, and the antixenosis and antibiosis categories are ambiguous and inseparable in practice. These features have perhaps led to a simplistic approach to understanding arthropod resistance in crop plants. A dichotomous scheme is proposed as a replacement, with a major division between resistance (plant traits that limit injury to the plant) and tolerance (plant traits that reduce amount of yield loss per unit injury), and the resistance category subdivided into constitutive/inducible and direct/indirect subcategories. The most important benefits of adopting this dichotomous scheme are to more closely align the basic and applied literatures on plant resistance and to encourage a more mechanistic approach to studying plant resistance in crop plants. A more mechanistic approach will be needed to develop novel approaches for integrating plant resistance into pest management programs. 相似文献
4.
ERIC F. LOPRESTI PATRICK GROF‐TISZA MORIA ROBINSON JESSIE GODFREY RICHARD KARBAN 《Ecological Entomology》2018,43(2):154-161
1. Abrasive material in the diet of herbivorous organisms comes from a variety of sources, including crystalline silica or calcium in plant tissues, accidentally ingested soil while digging or grazing, and entrapped substrate on the surfaces of plants. A wide variety of plants entrap substrate, usually with glandular trichomes. 2. A previous study demonstrated that entrapped sand provided resistance to herbivory in the field. In this study, the following questions were addressed: how does entrapped sand on Abronia latifolia (Nyctaginaceae) leaves and stems affect preference and performance of a common herbivore, the large‐bodied caterpillar Hyles lineata (Sphingidae); does this effect differ from those experienced by an internally feeding leaf miner? 3. Using a combination of experimental and observational approaches, it was found that sand comprised ～4–5% of ingested weight during normal feeding of H. lineata caterpillars. This entrapped sand caused extensive wear to their mandibles, they avoided sand‐covered plants when given the choice, and the sand negatively impacted performance metrics, including pupal weight, development time, and growth rate. In contrast, a leaf‐mining caterpillar did not have a preference for or against feeding on sandy plants. 4. These results are similar to studies on mandibular wear due to grasses, and herbivorous insects that feed on these two plant groups may have similar morphologies. It is hypothesised that increased wear potential may be a convergent solution to abrasive plants in both mammals (hypsodonty) and insects. 相似文献
5.
Defense priming is defined as increased readiness of defense induction. A growing body of literature indicates that plants (or intact parts of a plant) are primed in anticipation of impending environmental stresses, both biotic and abiotic, and upon the following stimulus, induce defenses more quickly and strongly. For instance, some plants previously exposed to herbivore‐inducible plant volatiles (HIPVs) from neighboring plants under herbivore attack show faster or stronger defense activation and enhanced insect resistance when challenged with secondary insect feeding. Research on priming of antiherbivore defense has been limited to the HIPV‐mediated mechanism until recently, but significant advances were made in the past three years, including non‐HIPV‐mediated defense priming, epigenetic modifications as the molecular mechanism of priming, and others. It is timely to consider the advances in research on defense priming in the plant–insect interactions. 相似文献
6.
We compared the effects of a sesquiterpene (ST, cacalol) and a pyrrolizidine alkaloid (PA, seneciphylline), both occurring in Adenostyles alliariae, on food choice and performance of specialist and generalist insect herbivores which are all known to feed or live on A. alliariae. In choice experiments we investigated whether the compounds were preferred, deterrent or had no effect. All specialist species Aglaostigma discolor (Hymenoptera, Tenthredinidae), Oreina cacaliae (Coleoptera, Chrysomelidae) and O. speciosissima avoided feeding when confronted with the combination of compounds. Only larvae of A. discolor avoided the single ST treatment as well. Larvae of the generalist species Callimorpha dominula (Lepidoptera, Arctiidae), Cylindrotoma distinctissima (Diptera, Tipulidae) and Miramella alpina (Caelifera, Acrididae) generally avoided feeding from PA, ST and PAST treatments. The only exception were caterpillars of C. dominula which were indiscriminate towards PA when naive, and preferred to feed on the PA treatment when they had experienced the compound before. Performance, measured as the growth of larvae on the different treatments in a no choice situation over a period of 10–17 days, was not different between treatments in the specialist leaf beetles O. cacaliae and O. speciosissima. Their avoidance of the combination treatment in the choice experiments had no obvious effect on growth when forced to feed from the treatment. In the generalist C. dominula only the high concentration combination treatment (PAST) reduced growth of the larvae due to decreased consumption. In C. distinctissima we found reduced growth in all treatments except one (PA3%). Poor growth performance in C. distinctissima was due to postingestive physiological effects of all treatments and additionally to consumption reduction in high‐dose ST treatments. Genetic variability (broad sense heritability) of growth performance metabolism varied in accordance with the specialization degree of the species. O. cacaliae, the most specialized species, had no significant heritability; O. speciosissima, the less specialized specialist, had a heritability of 0.46; C. dominula, the PA adapted generalist species, had a heritability of 0.64; C. distinctissima, the generalist with no apparent adaptations, had a heritability of 0.84. 相似文献
7.
Katherine E. Clark Rex M. Brennan Katrin MacKenzie Scott N. Johnson 《Agricultural and Forest Entomology》2012,14(2):157-163
- 1 The vine weevil Otiorhynchus sulcatus is a major pest of horticultural crops worldwide, with root‐feeding larvae causing most damage. Adult oviposition aboveground may therefore influence levels of damage as the larvae are relatively immobile after oviposition.
- 2 The present study investigated feeding and oviposition behaviour on red raspberry Rubus idaeus using intact plants, ensuring that choices reflected the realistic differences in cultivar appearance and chemical composition. Previous studies investigating vine weevil feeding and oviposition on other crops have used excised plant material, which may inadvertently influence behaviour.
- 3 Adult weevils significantly preferred to feed on particular cultivars in the choice experiment (e.g. Tulameen), although they consumed significantly more foliage (0.22–1.03 cm2/day) on different raspberry cultivars (e.g. Glen Moy, Glen Rosa and a wild accession) in no‐choice situations.
- 4 In choice experiments, weevils tended to avoid laying eggs on some cultivars (e.g. Glen Moy and the wild accession). The number of eggs laid (1.91–4.32 eggs per day) did not, however, differ significantly between the cultivars in a no‐choice situation. Foliar nitrogen and magnesium concentrations were positively, although weakly, correlated with the total number of eggs laid.
- 5 The present study highlights the importance of considering both choice and no‐choice tests when assessing crop susceptibility to attack because weevils may avoid feeding on certain cultivars (e.g. Glen Moy) when given a choice, although this would cause significant damage to such cultivars if they were grown in monoculture (i.e. when there is no alternative).
8.
Madhav P. Thakur Vera Quast Nicole M. van Dam Nico Eisenhauer Christiane Roscher Arjen Biere Ainhoa Martinez‐Medina 《Oikos》2019,128(8):1136-1146
Plants form mutualistic relationship with a variety of belowground fungal species. Such a mutualistic relationship can enhance plant growth and resistance to pathogens. Yet, we know little about how interactions between functionally diverse groups of fungal mutualists affect plant performance and competition. We experimentally determined the effects of interaction between two functional groups of belowground fungi that form mutualistic relationship with plants, arbuscular mycorrhizal (AM) fungi and Trichoderma, on interspecific competition between pairs of closely related plant species from four different genera. We hypothesized that the combination of two functionally diverse belowground fungal species would allow plants and fungi to partition their symbiotic relationships and relax plant–plant competition. Our results show that: 1) the AM fungal species consistently outcompeted the Trichoderma species independent of plant combinations; 2) the fungal species generally had limited effects on competitive interactions between plants; 3) however, the combination of fungal species relaxed interspecific competition in one of the four instances of plant–plant competition, despite the general competitive superiority of AM fungi over Trichoderma. We highlight that the competitive outcome between functionally diverse fungal species may show high consistency across a broad range of host plants and their combinations. However, despite this consistent competitive hierarchy, the consequences of their interaction for plant performance and competition can strongly vary among plant communities. 相似文献
9.
Variation in plant traits among plant species may promote the development of a characteristic functional assemblage of insect herbivores associated with each plant species. However, only a small number of studies have detailed the representation of several herbivore guilds among co‐occurring plant species to determine whether the functional structure of herbivorous insect assemblages varies widely and consistently among plant species. The present study provides one of the few published data sets reporting on the density of several guilds of insect herbivores among numerous plant species. Variation in guild associations with plant phenology and season are also described. Insect herbivores were divided into 10 guilds, and the representation of these guilds was examined for 18 co‐occurring plant species. Guild densities and assemblage composition varied significantly among plant species, even when variation over time was taken into account. Variation in guild densities and assemblage composition were not strongly related to the taxonomic relationships of the plants. The highest densities of several guilds occurred in spring and summer, although other guilds were not strongly seasonal. Certain guilds were strongly associated with the presence of new leaves, whereas other guilds appeared to prefer mature leaves. This resulted in assemblage differences between samples containing new and mature leaves and samples containing mature leaves only. Even though the timing and duration of leaf and flower production varied among plant species, this did not explain all variation in guild densities among plant species. It is suggested that additional factors, including plant traits, are contributing to the wide and consistent variation in herbivore assemblage composition among plant species. 相似文献
10.
Antonino Cusumano Feng Zhu Anne‐Nathalie Volkoff Patrick Verbaarschot Janneke Bloem Heiko Vogel Marcel Dicke Erik H. Poelman 《Ecology letters》2018,21(7):957-967
Microbial mutualistic symbiosis is increasingly recognised as a hidden driving force in the ecology of plant–insect interactions. Although plant‐associated and herbivore‐associated symbionts clearly affect interactions between plants and herbivores, the effects of symbionts associated with higher trophic levels has been largely overlooked. At the third‐trophic level, parasitic wasps are a common group of insects that can inject symbiotic viruses (polydnaviruses) and venom into their herbivorous hosts to support parasitoid offspring development. Here, we show that such third‐trophic level symbionts act in combination with venom to affect plant‐mediated interactions by reducing colonisation of subsequent herbivore species. This ecological effect correlated with changes induced by polydnaviruses and venom in caterpillar salivary glands and in plant defence responses to herbivory. Because thousands of parasitoid species are associated with mutualistic symbiotic viruses in an intimate, specific relationship, our findings may represent a novel and widespread ecological phenomenon in plant–insect interactions. 相似文献
11.
Micaela Buteler David K. Weaver Perry R. Miller 《Agricultural and Forest Entomology》2008,10(4):347-354
1 Parasitoids Bracon cephi (Gahan) and Bracon lissogaster Muesebeck and their herbivorous host the wheat stem sawfly Cephus cinctus Norton, a pest of wheat Triticum aestivum, were investigated for yield in T. aestivum grown in the field. 2 Wheat stem sawfly‐infested stems had a higher yield potential than uninfested stems. However, final reproductive output was not significantly different between ears on infested stems that supported complete larval development compared with ears on uninfested stems. 3 Stems containing parasitized larvae and stems containing larvae that died before completing their development had a higher mean number of seeds and seed weight, when accounting for number of fertile spikelets of each ear, than either infested with live larvae and uninfested stems. 4 The results obtained suggest that larval feeding prevented infested stems from attaining their yield potential, and that the negative impact of the pest on wheat yield was reduced when late instar sawfly larvae were parasitized. Even though some feeding occurs before parasitism, this early damage has a comparatively low impact on yield. 5 This is the first study to show a yield benefit and enhanced plant fitness due to the wheat stem sawfly parasitoids B. cephi and B. lissogaster. This results from the maintenance of increased seed number and seed weight in the higher yielding stems that are preferentially infested by this pest. 相似文献
12.
Pekka Kaitaniemi Kai Ruohomki 《Perspectives in Plant Ecology, Evolution and Systematics》2003,5(4):231-249
We present a comprehensive analysis of factors affecting resource allocation and crown formation in a subarctic birch tree, Betula pubescens ssp. czerepanovii (Orlova) Hämet-Ahti. Using biomass measurements and digitized data on tree architecture, we investigated several hypotheses on various factors that may modify plant growth. We also analyzed the extent to which different mechanisms operate at different scales, ranging from individual shoots to the whole branches or trees. Different factors affected allocation at different levels of organization. Stem age had a minor effect, suggesting that similar control mechanisms operate at all stages of development. Fates of individual shoots were affected by their local growing conditions as indicated, for example, by the dependence of long shoot production on light. Buds formed in the current long shoots were likely to become new long shoots. In the innermost crown parts, radial growth had priority compared to long shoot production. Elongation of individual long shoots was controlled by two conflicting factors. Long distance from the roots suppressed growth, probably indicating costs associated with resource transportation, whereas a high level of light augmented growth. In contrast, growth of entire branches was not so clearly related to the availability of resources, but showed limitation due to allometric scaling. This set a relationship between the maximum long shoot number and the overall branch size, and may indicate allometric constraints to the way a tree is constructed. Strict allometric relationships existed also between other structural traits of mountain birch, most of them similar at all levels of branching hierarchy. However, despite the upper level restrictions set by allometry, source-sink interactions and localized responses of individual shoots operated as local processes that directed allocation towards the most favourable positions. This may be a mechanism for achieving efficient tree architecture in terms of resource intake and costs of transportation. 相似文献
13.
Volatile organic compounds (VOCs) emitted by plant roots can influence the germination and growth of neighbouring plants. However, little is known about the effects of root VOCs on plant–herbivore interactions of neighbouring plants. The spotted knapweed (Centaurea stoebe) constitutively releases high amounts of sesquiterpenes into the rhizosphere. Here, we examine the impact of C. stoebe root VOCs on the primary and secondary metabolites of sympatric Taraxacum officinale plants and the resulting plant‐mediated effects on a generalist root herbivore, the white grub Melolontha melolontha. We show that exposure of T. officinale to C.stoebe root VOCs does not affect the accumulation of defensive secondary metabolites but modulates carbohydrate and total protein levels in T. officinale roots. Furthermore, VOC exposure increases M. melolontha growth on T. officinale plants. Exposure of T. officinale to a major C. stoebe root VOC, the sesquiterpene (E)‐β‐caryophyllene, partially mimics the effect of the full root VOC blend on M. melolontha growth. Thus, releasing root VOCs can modify plant–herbivore interactions of neighbouring plants. The release of VOCs to increase the susceptibility of other plants may be a form of plant offense. 相似文献
14.
Marko J. Spasojevic Susan Harrison Howard W. Day Randal J. Southard 《Ecology letters》2014,17(6):700-709
One important but largely unanswered question about floristic responses to climate change is how interactions such as competition, facilitation and plant–soil feedbacks will influence the ability of species to track shifting climates. In a rugged and moisture‐limited region that has recently warmed by 2° (Siskiyou Mountains, OR, USA), we planted three species into cooler aspects and elevations than those they currently inhabit, with and without removal of neighbouring plants, and tracked them over 2 years. Two species had higher success in cooler topographic locations, and this success was enhanced by neighbouring plants, which appeared to modulate minimum growing season temperatures. One species' success was also facilitated by the higher soil organic matter found in cooler sites. These results are a novel experimental demonstration of two important factors that may buffer climate change impacts on plants: rugged topography and plant–plant facilitation. 相似文献
15.
Anna K. Knuff Michael Staab Julian Frey Jan Helbach Alexandra‐Maria Klein 《Ecological Entomology》2019,44(6):833-843
1. How herbivore plant diversity relationships are shaped by the interplay of biotic and abiotic environmental variables is only partly understood. For instance, plant diversity is commonly assumed to determine abundance and richness of associated specialist herbivores. However, this relationship can be altered when environmental variables such as temperature covary with plant diversity. 2. Using gall‐inducing arthropods as focal organisms, biotic and abiotic environmental variables were tested for their relevance to specialist herbivores and their relationship to host plants. In particular, the hypothesis that abundance and richness of gall‐inducing arthropods increase with plant richness was addressed. Additionally, the study asked whether communities of gall‐inducing arthropods match the communities of their host plants. 3. Neither abundance nor species richness of gall‐inducing arthropods was correlated with plant richness or any other of the tested environmental variables. Instead, the number of gall species found per plant decreased with plant richness. This indicates that processes of associational resistance may explain the specialised plant herbivore relationship in our study. 4. Community composition of gall‐inducing arthropods matched host plant communities. In specialised plant herbivore relationships, the presence of obligate host plant species is a prerequisite for the occurrence of its herbivores. 5. It is concluded that the abiotic environment may only play an indirect role in shaping specialist herbivore communities. Instead, the occurrence of specialist herbivore communities might be best explained by plant species composition. Thus, plant species identity should be considered when aiming to understand the processes that shape diversity patterns of specialist herbivores. 相似文献
16.
Elizabeth S. Jeffers Nicki J. Whitehouse Adrian Lister Gill Plunkett Phil Barratt Emma Smyth Philip Lamb Michael W. Dee Stephen J. Brooks Katherine J. Willis Cynthia A. Froyd Jenny E. Watson Michael B. Bonsall 《Ecology letters》2018,21(6):814-825
Plants and animals influence biomass production and nutrient cycling in terrestrial ecosystems; however, their relative importance remains unclear. We assessed the extent to which mega‐herbivore species controlled plant community composition and nutrient cycling, relative to other factors during and after the Late Quaternary extinction event in Britain and Ireland, when two‐thirds of the region's mega‐herbivore species went extinct. Warmer temperatures, plant–soil and plant–plant interactions, and reduced burning contributed to the expansion of woody plants and declining nitrogen availability in our five study ecosystems. Shrub biomass was consistently one of the strongest predictors of ecosystem change, equalling or exceeding the effects of other biotic and abiotic factors. In contrast, there was relatively little evidence for mega‐herbivore control on plant community composition and nitrogen availability. The ability of plants to determine the fate of terrestrial ecosystems during periods of global environmental change may therefore be greater than previously thought. 相似文献
17.
ROXINA SOLER SONJA V. SCHAPER T. MARTIJN BEZEMER ANNE M. CORTESERO THOMAS S. HOFFMEISTER WIM H. VAN DER PUTTEN LOUISE E. M. VET JEFFREY A. HARVEY 《Ecological Entomology》2009,34(3):339-345
Abstract 1. Several studies have shown that above‐ and belowground insects can interact by influencing each others growth, development, and survival when they feed on the same host‐plant. In natural systems, however, insects can make choices on which plants to oviposit and feed. A field experiment was carried out to determine if root‐feeding insects can influence feeding and oviposition preferences and decisions of naturally colonising foliar‐feeding insects. 2. Using the wild cruciferous plant Brassica nigra and larvae of the cabbage root fly Delia radicum as the belowground root‐feeding insect, naturally colonising populations of foliar‐feeding insects were monitored over the course of a summer season. 3. Groups of root‐infested and root‐uninfested B. nigra plants were placed in a meadow during June, July, and August of 2006 for periods of 3 days. The root‐infested and the root‐uninfested plants were either dispersed evenly or placed in clusters. Once daily, all leaves of each plant were carefully inspected and insects were removed and collected for identification. 4. The flea beetles Phyllotreta spp. and the aphid Brevicoryne brassicae were significantly more abundant on root‐uninfested (control) than on root‐infested plants. However, for B. brassicae this was only apparent when the plants were placed in clusters. Host‐plant selection by the generalist aphid M. persicae and oviposition preference by the specialist butterfly P. rapae, however, were not significantly influenced by root herbivory. 5. The results of this study show that the presence of root‐feeding insects can affect feeding and oviposition preferences of foliar‐feeding insects, even under natural conditions where many other interactions occur simultaneously. The results suggest that root‐feeding insects play a role in the structuring of aboveground communities of insects, but these effects depend on the insect species as well as on the spatial distribution of the root‐feeding insects. 相似文献
18.
Hao Xu Gaylord Desurmont Thomas Degen Guoxin Zhou Diane Laplanche Luka Henryk Ted C.J. Turlings 《Plant, cell & environment》2017,40(3):330-339
Herbivore‐induced plant volatiles (HIPVs) are important cues for female parasitic wasps to find hosts. Here, we investigated the possibility that HIPVs may also serve parasitoids as cues to locate mates. To test this, the odour preferences of four braconid wasps – the gregarious parasitoid Cotesia glomerata (L.) and the solitary parasitoids Cotesia marginiventris (Cresson), Microplitis rufiventris Kokujev and Microplitis mediator (Haliday) – were studied in olfactometers. Each species showed attraction to pheromones but in somewhat different ways. Males of the two Cotesia species were attracted to virgin females, whereas females of M. rufiventris were attracted to virgin males. Male and female M. mediator exhibited attraction to both sexes. Importantly, female and male wasps of all four species were strongly attracted by HIPVs, independent of mating status. In most cases, male wasps were also attracted to intact plants. The wasps preferred the combination of HIPVs and pheromones over plant odours alone, except M. mediator, which appears to mainly use HIPVs for mate location. We discuss the ecological contexts in which the combined use of pheromones and HIPVs by parasitoids can be expected. To our knowledge, this is the first study to show that braconid parasitoids use HIPVs and pheromones in combination to locate mates. 相似文献
19.
Paul J. CaraDonna Laura A. Burkle Benjamin Schwarz Julian Resasco Tiffany M. Knight Gita Benadi Nico Blüthgen Carsten F. Dormann Qiang Fang Jochen Fründ Benoit Gauzens Christopher N. Kaiser‐Bunbury Rachael Winfree Diego P. Vzquez 《Ecology letters》2021,24(1):149-161
Most studies of plant–animal mutualistic networks have come from a temporally static perspective. This approach has revealed general patterns in network structure, but limits our ability to understand the ecological and evolutionary processes that shape these networks and to predict the consequences of natural and human‐driven disturbance on species interactions. We review the growing literature on temporal dynamics of plant–animal mutualistic networks including pollination, seed dispersal and ant defence mutualisms. We then discuss potential mechanisms underlying such variation in interactions, ranging from behavioural and physiological processes at the finest temporal scales to ecological and evolutionary processes at the broadest. We find that at the finest temporal scales (days, weeks, months) mutualistic interactions are highly dynamic, with considerable variation in network structure. At intermediate scales (years, decades), networks still exhibit high levels of temporal variation, but such variation appears to influence network properties only weakly. At the broadest temporal scales (many decades, centuries and beyond), continued shifts in interactions appear to reshape network structure, leading to dramatic community changes, including loss of species and function. Our review highlights the importance of considering the temporal dimension for understanding the ecology and evolution of complex webs of mutualistic interactions. 相似文献
20.
1. When herbivores of distinct feeding guilds, such as phloem feeders and leaf chewers, interact, the outcome of these interactions often shows facilitation. However, whether this facilitation turns into competition at stronger herbivory pressure remains unknown. 2. Using an integrative approach that links ecological processes (behavioural choices of insects) with physiological plant mechanisms (nutrient and phytohormone levels) for the wild crucifer Brassica nigra (L.) Koch., this study evaluates preferences of leaf chewers for plants previously infested with several densities of the specialist aphid Brevicoryne brassicae L. (Hemiptera, Aphididae). As leaf chewers, four species of caterpillars (Lepidoptera) were selected that differ in their degree of specialisation in crucifers. 3. These results show that, whereas at low and medium aphid densities caterpillars displayed a preference for aphid‐infested plants or no preference, at high aphid infestation density, all four species of caterpillar preferred uninfested plants, with a significant difference for Pieris rapae and Mamestra brassicae. 4. In contrast to our expectation, the consistent preference for uninfested plants at a high aphid density could not be associated with a decrease in plant nutrition. However, while jasmonate concentrations [i.e. 12‐oxo‐phytodienoic acid and jasmonic acid (JA)] at medium aphid‐density infestation decreased compared with low levels of infestation, at high infestation level, the jasmonates JA as well as JA conjugated with the amino acid isoleucine were present at higher levels compared with low‐infestation treatments. 5. This work provides evidence that positive interactions observed in herbivore communities can be transient, leading to negative interactions mediated by changes in plant defences rather than in plant nutrition. 相似文献