Types Of Herbivores Research Articles

Red oak responses to nitrogen addition depend on herbivory type, tree family, and site

Elevated atmospheric N deposition is predicted to increase plant growth and C storage in N-limited systems, but this assumes that no mitigating ecological factors are influenced by N deposition. Many herbivores are also N-limited and so increased herbivore damage in response to N deposition may moderate, or even eliminate, gains in plant growth under elevated N. Thus the response of herbivores to N deposition could influence the onset and magnitude of N saturation resulting in expedited decreases in C storage. Since tree susceptibility to herbivores is partially under genetic control and will be influenced by site characteristics, we tested whether the interaction between N deposition, tree growth, and herbivore damage depends on tree genetic variation in susceptibility to herbivores at different locations. By monitoring 12 half-sib families of northern red oak ( Quercus rubra) saplings at two common garden sites in south-central Pennsylvania, we found that herbivores were pervasive at both sites, resulting in 13% chewing damage, 16% galling damage and 28% browsing damage. N addition significantly affected browsing damage (8% overall increase) and chewing damage (19% overall increase) but did not affect galling damage. However, this effect was strongly dependent on the Q. rubra family and location, both of which influenced oak susceptibility to herbivore damage independent of N additions. Greater browsing damage on trees under N addition caused reductions in relative height growth, and this effect also depended on tree family and location. Our result suggests that herbivory, mediated by tree genetic lineage and site-specific conditions, may represent an important component of C sinks and N saturation under elevated N deposition.

Exotic vertebrate and invertebrate herbivores differ in their impacts on native and exotic plants: a meta-analysis

Herbivores modify various ecological processes including interactions between native and exotic plants that may affect invasion success by the exotic plants. It is unknown whether different types of exotic herbivores have similar effects on native and exotic plants. Using two distinct data sets, we ran meta-analyses to compare exotic vertebrate and invertebrate herbivore preferences for, and effects on performance and population sizes of native and exotic plants. We found that exotic vertebrate herbivores have positive effects on exotic plant performance and population sizes, and no significant effects on native plants. Exotic invertebrates have significant negative effects on performance and population sizes of both exotic and native plants. Vertebrates prefer to feed on native plants relative to exotic plants, while invertebrates prefer the exotic plants to native plants. Thus the exotic vertebrate herbivores may aid invasiveness of exotic plants, in accordance with the invasional meltdown hypothesis, while exotic invertebrate herbivores probably have no net effect on invasion process of the exotic plants. Invertebrate herbivore preferences for exotic plants support the biotic resistance hypothesis, as the native plants probably resist the invertebrate herbivory. We also tested an evolutionary logic that posits that herbivores with similar evolutionary history as plants will affect the plants less negatively than plants with which they have not co-evolved. Our results indicate that there is no consistent pattern in effects of exotic vertebrate and invertebrate herbivores on exotic plants with or without which they have co-evolved.

Above- and below-ground vertebrate herbivory may each favour a different subordinate species in an aquatic plant community

At least two distinct trade-offs are thought to facilitate higher diversity in productive plant communities under herbivory. Higher investment in defence and enhanced colonization potential may both correlate with decreased competitive ability in plants. Herbivory may thus promote coexistence of plant species exhibiting divergent life history strategies. How different seasonally tied herbivore assemblages simultaneously affect plant community composition and diversity is, however, largely unknown. Two contrasting types of herbivory can be distinguished in the aquatic vegetation of the shallow lake Lauwersmeer. In summer, predominantly above-ground tissues are eaten, whereas in winter, waterfowl forage on below-ground plant propagules. In a 4-year exclosure study we experimentally separated above-ground herbivory by waterfowl and large fish in summer from below-ground herbivory by Bewick’s swans in winter. We measured the individual and combined effects of both herbivory periods on the composition of the three-species aquatic plant community. Herbivory effect sizes varied considerably from year to year. In 2 years herbivore exclusion in summer reinforced dominance of Potamogeton pectinatus with a concomitant decrease in Potamogeton pusillus, whereas no strong, unequivocal effect was observed in the other 2 years. Winter exclusion, on the other hand, had a negative effect on Zannichellia palustris, but the effect size differed considerably between years. We suggest that the colonization ability of Z. palustris may have enabled this species to be more abundant after reduction of P. pectinatus tuber densities by swans. Evenness decreased due to herbivore exclusion in summer. We conclude that seasonally tied above- and below-ground herbivory may each stimulate different components of a macrophyte community as they each favoured a different subordinate plant species.

Quantification of Information in a One-Way Plant-to-Animal Communication System

In order to demonstrate possible broader applications of information theory to the quantification of non-human communication systems, we apply calculations of information entropy to a simple chemical communication from the cotton plant (Gossypium hirsutum) to the wasp (Cardiochiles nigriceps) studied by DeMoraes et al. The purpose of this chemical communication from cotton plants to wasps is presumed to be to allow the predatory wasp to more easily obtain the location of its preferred prey—one of two types of parasitic herbivores feeding on the cotton plants. Specification of the plant-eating herbivore feeding on it by the cotton plants allows preferential attraction of the wasps to those individual plants. We interpret the emission of nine chemicals by the plants as individual signal differences, (depending on the herbivore type), to be detected by the wasps as constituting a nine-signal one-way communication system across kingdoms (from the kingdom Plantae to the kingdom Animalia). We use fractional differences in the chemical abundances, (emitted as a result of the two herbivore types), to calculate the Shannon information entropic measures (marginal, joint, and mutual entropies, as well as the ambiguity, etc. of the transmitted message). We then compare these results with the subsequent behavior of the wasps, (calculating the equivocation in the message reception), for possible insights into the history and actual working of this one-way communication system.

Expression of BrD1, a plant defensin from Brassica rapa, confers resistance against brown planthopper (Nilaparvata lugens) in transgenic rices.

Plant defensins are small (5-10 kDa) basic peptides thought to be an important component of the defense pathway against fungal and/or bacterial pathogens. To understand the role of plant defensins in protecting plants against the brown planthopper, a type of insect herbivore, we isolated the Brassica rapa Defensin 1 (BrD1) gene and introduced it into rice (Oryza sativa L.) to produce stable transgenic plants. The BrD1 protein is homologous to other plant defensins and contains both an N-terminal endoplasmic reticulum signal sequence and a defensin domain, which are highly conserved in all plant defensins. Based on a phylogenetic analysis of the defensin domain of various plant defensins, we established that BrD1 belongs to a distinct subgroup of plant defensins. Relative to the wild type, transgenic rices expressing BrD1 exhibit strong resistance to brown planthopper nymphs and female adults. These results suggest that BrD1 exhibits insecticidal activity, and might be useful for developing cereal crop plants resistant to sap-sucking insects, such as the brown planthopper.

Fitness effects and genetic architecture of plant–herbivore interactions in sunflower crop–wild hybrids

*Introgression of cultivar alleles into wild plant populations via crop-wild hybridization is primarily governed by their fitness effects as well as those of linked loci. The fitness of crop-wild hybrids is often dependent on environmental factors, but less is understood about how aspects of the environment affect individual cultivar alleles. *This study investigated the effects of naturally occurring herbivory on patterns of phenotypic selection and the genetic architecture of plant-herbivore interactions in an experimental sunflower crop-wild hybrid population in two locales. *Phenotypic selection analyses suggested that cultivar alleles conferring increased size were generally favored, but at one site cultivar-like flowering time was favored only if three types of herbivory were included in the selection model. Quantitative trait locus (QTL) mapping identified three regions in which the cultivar allele conferred a selective advantage for a number of co-localized traits. Quantitative trait loci for several measures of insect herbivory were detected and, although the cultivar allele increased herbivory damage at the majority of these QTLs, they rarely colocalized with advantageous cultivar alleles for morphological traits. *These results suggest that a subset of cultivar traits/alleles are advantageous in natural environments but that herbivory may mitigate the selective advantage of some cultivar alleles.

Specialized Feeding Modes Promote Coexistence of Competing Herbivores: Insights From a Metabolic Pool Model

Competition theory suggests that a single resource should support one consumer species. However, competitive exclusion may be relaxed by periodic disturbances, temporal or spatial segregation of consumers, or fine-scale resource partitioning. This last mechanism may be especially common for competing phytophagous insects. Unlike many predators, herbivores rarely consume their entire prey item and often have specialized feeding modes on specific plant parts. Thus, different herbivore guilds may "avoid" each other, thereby facilitating their coexistence. I analyzed a simplified metabolic pool model that includes two herbivore types: a "leaf chewer" and a "phloem feeder." Phytophagous insects with the same feeding mode never coexisted, but different guilds may coexist stably-depending on productivity of the carbohydrate pool, allocation to vegetative biomass, and defoliation rate. Differences in herbivore feeding mode are equivalent to fine scale resource partitioning, potentially within the individual plant. Thus, the addition of physiological detail changes the predictions of simple competition models and is relevant to weed biocontrol by informing decisions on which guilds of biocontrol agents to introduce.

Differential effects of defoliation by mopane caterpillars and pruning by African elephants on the regrowth of Colophospermum mopane foliage

Abstract:Plant responses to herbivory vary depending on herbivory type, yet the comparative effects of defoliation (e.g. by insects) and pruning (e.g. by large mammals) on a single tree species are poorly documented. We investigated this in the Northern Province of South Africa by comparing the regrowth of Colophospermum mopane trees previously defoliated by caterpillars or pruned by elephants, the two main browsers of C. mopane foliage. Shoots were up to 160% and 125% longer after natural (elephant) and simulated pruning and leaves ~25% longer in regrowth after natural pruning (n = 13–15 trees per treatment). Shoot density and chemical defences in leaves (tannin:protein ratio and total polyphenolic concentration) were, however, no different from control trees. Simulated defoliation resulted in statistically insignificant changes to regrowth in terms of leaf and shoot size (both slightly decreased) and shoot density (slightly increased). Natural (caterpillar) defoliation, however, resulted in regrowth with significantly decreased shoot and leaf size (about 50% and 20% of control lengths, respectively), as well as decreased leaf chemical defence. Shoot and leaf length were longer on trees flushing for the first time after pruning and late-season defoliation had a greater negative impact than mid-season defoliation. Despite the differences in regrowth characteristics after pruning and defoliation, mopane plants showed no apparent trade-off in investment between tolerance and resistance after either herbivory type, as neither regrowth nor chemical defence occurred at the expense of the other.

Grazing orchids: impact of florivory on two species of Caladenia (Orchidaceae)

Herbivory is considered a major threat in many of the orchid-species recovery plans in Australia. Kangaroos and rabbits are the most commonly implicated herbivores; however, no studies have attempted to confirm their role. Regular monitoring of several populations of Caladenia rigida R.S.Rogers and C. tentaculata Schldl. during 3 years in the Mount Lofty Ranges, South Australia, revealed that up to 94% of flowers and 36% of seed capsules were browsed, whereas leaf herbivory was less prevalent. Furthermore, patterns of herbivory varied markedly among sites and across years. In two seasons, predation of C. rigida flowers inside a kangaroo- and rabbit-proof exclosure was equal to or higher than outside the exclosure. Florivory within populations was influenced by proximity to the habitat edge, although the direction of this response differed among sites. Various types of mesh cages were erected around plants to elucidate the size and type of herbivores. Plants protected from florivores were almost three times more likely to produce seed than were exposed plants; however, some cage types reduced pollination. Video surveillance confirmed the role of the white-winged chough, Corcorax melanorhamphos, as a florivore. The present study is the first one to identify a herbivore unequivocally, quantify the intensity and extent of floral herbivory across a range of populations, and assess the potential cost of florivory to the direct reproductive output of orchids.

Herbivore induction of the glucosinolate–myrosinase defense system: major trends, biochemical bases and ecological significance

Like many other plant defense compounds, glucosinolates are present constitutively in plant tissues, but are also induced to higher levels by herbivore attack. Of the major glucosinolate types, indolic glucosinolates are most frequently induced regardless of the type of herbivore involved. Over 90% of previous studies found that herbivore damage to glucosinolate-containing plants led to an increased accumulation of indolic glucosinolates at levels ranging up to 20-fold. Aliphatic and aromatic glucosinolates are also commonly induced by herbivores, though usually at much lower magnitudes than indolic glucosinolates, and aliphatic and aromatic glucosinolates may even undergo declines following herbivory. The glucosinolate defense system also requires another partner, the enzyme myrosinase, to hydrolyze the parent glucosinolates into biologically active derivatives. Much less is known about myrosinase induction after herbivory compared to glucosinolate induction, and no general trends are evident. However, it is clear that insect feeding stimulates the formation of various myrosinase associated proteins whose function is not yet understood. The biochemical mechanism of glucosinolate induction involves a jasmonate signaling cascade that leads eventually to increases in the transcript levels of glucosinolate biosynthetic genes. Several recently described transcription factors controlling glucosinolate biosynthesis are activated by herbivory or wounding. Herbivore induction of glucosinolates has sometimes been demonstrated to increase protection against subsequent herbivore attack, but more research is needed to evaluate the costs and benefits of this phenomenon.

Transcription factor MYC2 is involved in priming for enhanced defense during rhizobacteria‐induced systemic resistance in Arabidopsis thaliana

Upon appropriate stimulation, plants can develop an enhanced capacity to express infection-induced cellular defense responses, a phenomenon known as the primed state. Colonization of the roots of Arabidopsis thaliana by the beneficial rhizobacterial strain Pseudomonas fluorescens WCS417r primes the leaf tissue for enhanced pathogen- and insect-induced expression of jasmonate (JA)-responsive genes, resulting in an induced systemic resistance (ISR) that is effective against different types of pathogens and insect herbivores. Here the molecular mechanism of this rhizobacteria-induced priming response was investigated using a whole-genome transcript profiling approach. Out of the 1879 putative methyl jasmonate (MeJA)-responsive genes, 442 genes displayed a primed expression pattern in ISR-expressing plants. Promoter analysis of ISR-primed, MeJA-responsive genes and ISR-primed, Pseudomonas syringae pv. tomato DC3000 (Pst DC3000)-responsive genes revealed over-representation of the G-box-like motif 5'-CACATG-3'. This motif is a binding site for the transcription factor MYC2, which plays a central role in JA- and abscisic acid-regulated signaling. MYC2 expression was consistently up-regulated in ISR-expressing plants. Moreover, mutants impaired in the JASMONATE-INSENSITIVE1/MYC2 gene (jin1-1 and jin1-2) were unable to mount WCS417r-ISR against Pst DC3000 and the downy mildew pathogen Hyaloperonospora parasitica. Together, these results pinpoint MYC2 as a potential regulator in priming for enhanced JA-responsive gene expression during rhizobacteria-mediated ISR.

Specialization pays off: contrasting effects of two types of tannins on oak specialist and generalist moth species

Phytochemical coevolution theory posits that specialist herbivores will be less sensitive than generalists to the defensive compounds of their host. On the other hand, both types of herbivores should allegedly be similarly sensitive to ‘quantitative’ defences, such as tannin compounds. In this paper, we critically examine the biological effects of two types of tannins: vescalagin (a quantitatively dominant hydrolysable tannin of Quercus robur), and a mix of condensed tannins. In a phylogenetically controlled design, we compare the response of two specialist moth species (Dichonia aprilina and Catocala sponsa) and two generalist species (Acronicta psi and Amphipyra pyramidea) to four artificial diets: a control diet, a diet with 50 mg g−1 vescalagin, a diet with 15 mg/g condensed tannins, and a diet with both 50 mg g−1 vescalagin and 15 mg g−1 condensed tannins. Overall, we find drastic effects of vescalagin and pronounced differences in the responses of generalist and specialist herbivores, but no detectable effects of condensed tannins, and no interaction between the two types of compounds. More specifically, vescalagin reduced the growth of generalist species to one‐half of control levels over 72 h. The compound served as a strong feeding deterrent to generalists, reducing ingestion rates by two‐thirds. Vescalagin also reduced the metabolic and growth efficiency of generalist species to between 16% and 56% of control levels – effects which were lacking or even reversed in specialist species. These patterns suggest that vescalagin forms an important part of the oak's defence against herbivores, and that specialist species have adapted to deal with such substances. In terms of biological effects, condensed tannins seem much less important. Given a quantitative dominance of hydrolysable tannins over condensed tannins in oak leaves, and a seasonal decline in overall tannin levels, these findings contradict the previous notion that widespread spring feeding among oak herbivores could be attributed to tannins.

Simulated herbivory induces extrafloral nectary production in Prunus avium

1. Induced chemical responses to herbivory have been widely documented, however less attention has been given to the induced morphological defences, particularly those that mediate protection mutualisms. One of the most widely studied mutualisms is the ant-plant protection mutualism, in which ants and other predatory arthropods defend plants against herbivores in exchange for food or housing. 2. Chemical and morphological traits that mediate this protection mutualism attract beneficial partners to plants. Thus induction of traits can lead to greater protection by mutualists when herbivores are present. In this study we examined whether extrafloral nectaries (EFNs) are induced in response to simulated herbivory in Prunus avium. 3. In a greenhouse experiment, continuous damage to seedlings was simulated in two treatments intended to mimic different types of herbivores: (i) 50% of the area of each leaf was removed using a paper hole punch (e.g. insect herbivore simulation), and (ii) 50% of the area of each leaf was removed using scissors (e.g. browsing mammal simulation). Seedlings in the control group were not damaged. 4. Post-treatment, damaged plants produced significantly more EFNs per leaf on pre-existing leaves, as well as those that emerged following the onset of damage, than plants in the control group. Regardless of treatment, leaves emerging earlier supported fewer EFNs than leaves emerging later in the experiment. 5. Allocation to defence by seedlings, which have limited resources available, suggests the protection mutualism could be important to plant fitness in the field. Further study of patterns of EFN induction in P. avium seedlings is needed to better understand the significance of this induced response.

Herbivory in gingers from latest Cretaceous to present: is the ichnogenus Cephaloleichnites (Hispinae, Coleoptera) a rolled-leaf beetle?

It is suggested that rolled-leaf hispine beetles (Hispinae, Coleoptera) and plants from the order Zingiberales maintained a highly specialized plant-herbivore interaction for >60 My. The evidence supporting this old and conservative interaction are herbivory marks found on leaves of the genus Zingiberopsis (Zingiberaceae) from the latest Cretaceous and early Eocene. This fossil herbivory was described as the ichnotaxon Cephaloleichnites strongii (Hispinae, Coleoptera), based on the assumption that this type of herbivory can be solely attributed to extant rolled-leaf beetles. This ichnotaxon has been a key element in several analyses on the origin, radiation and diversification of tropical insect herbivores. In this paper we report feeding patterns equivalent to those described in Zingiberopsis fossils but produced by larvae of Pyralidae and Choreutidae (Lepidoptera) and Anopsilus weevils (Curculionidae, Coleoptera) in four families of extant Zingiberales. We discuss the implications of C. strongii not being a rolled leaf beetle and how this may affect the current knowledge of the co-diversification of rolled-leaf beetles and their host plants from the order Zingiberales.

Silencing jasmonate signalling and jasmonate‐mediated defences reveals different survival strategies between two Nicotiana attenuata accessions

To determine the impact of genotypic variation in secondary metabolite production on antiherbivore resistance and plant fitness, we genetically silenced biosynthetic genes for nicotine, trypsin proteinase inhibitors (TPI), and jasmonate (JA) production in two accessions of Nicotiana attenuata: one from Utah (UT) which responds to herbivory with JA-induced nicotine and TPI production, and one from Arizona (AZ) which is TPI-deficient but also produces JA-induced nicotine. Transient silencing of JA biosynthesis increased Manduca sexta larval growth on wild type (WT) plants of both accessions, but not on TPI-deficient UT or nicotine-deficient AZ lines, demonstrating that JA-mediated resistance to M. sexta requires TPIs in the UT and nicotine in the naturally TPI-deficient AZ accession. When transplanted into a native UT population, AZ and UT plants, rendered equally able or unable to produce nicotine and TPIs by stable transformation, received significantly different levels of herbivory. Both accessions differed in their resistance depending on the type of herbivores: resistance to rare, voracious herbivores (Saltatoria and Mammalia) was greater in AZ than UT lines, and dependent on nicotine production, while resistance to small, abundant herbivores (Coleoptera and Thysanoptera) was greater in UT lines, and dependent on TPI production. AZ lines produced more flowers and seed capsules than UT lines independently of TPI production costs. This fitness advantage was lost when accessions did not produce nicotine. We conclude that these two accessions have developed different survival strategies and thus differ in the cost-benefit functions of their JA-mediated defences.

Why Does Herbivore Attack Reconfigure Primary Metabolism?

A plant's resistance to herbivore attack is thought to be principally determined by its secondary metabolism, which can be remarkably plastic and responsive to different grades and types of herbivory. Newer unbiased “omic” approaches, which characterize transcriptomic, metabolomic, and proteomic

Plant Characteristics Associated with Natural Enemy Abundance at Michigan Native Plants

Habitat management is a type of conservation biological control that focuses on increasing natural enemy populations by providing them with plant resources such as pollen and nectar. Insects are known to respond to a variety of plant characteristics in their search for plant-provided resources. A better understanding of the specific characteristics used by natural enemy insects in selecting these resources could greatly improve efficiency in screening plants for habitat management. We examined 5 previously tested and widely recommended resource plants and 43 candidate plants to test whether the number and type of natural enemies and herbivores at each plant were predicted by plant characteristics including: period of peak bloom, floral area, maximum flower height, hue, chroma, and corolla size. Natural enemy abundance increased with week of peak bloom and greater floral area across all plants tested. Ordination of plant characteristics indicated that increasing floral area, period of peak bloom, maximum flower height, and decreasing corolla width grouped together into a single principal component. Both natural enemy and herbivore abundance increased significantly with the principal component for this set of characteristics, but the relationship with herbivore abundance was weaker. These results indicate that, for a given time of the season, selection of plants with the largest floral area has potential to increase natural enemy abundance in habitat management plantings and streamline plant selection for habitat management.

Positive and negative effects of grass, cattle, and wild herbivores on Acacia saplings in an East African savanna

Plant-plant interactions can be a complex mixture of positive and negative interactions, with the net outcome depending on abiotic and community contexts. In savanna systems, the effects of large herbivores on tree-grass interactions have rarely been studied experimentally, though these herbivores are major players in these systems. In African savannas, trees often become more abundant under heavy cattle grazing but less abundant in wildlife preserves. Woody encroachment where cattle have replaced wild herbivores may be caused by a shift in the competitive balance between trees and grasses. Here we report the results of an experiment designed to quantify the positive, negative, and net effects of grasses, wild herbivores, and cattle on Acacia saplings in a Kenyan savanna. Acacia drepanolobium saplings under four long-term herbivore regimes (wild herbivores, cattle, cattle + wild herbivores, and no large herbivores) were cleared of surrounding grass or left with the surrounding grass intact. After two years, grass-removal saplings exhibited 86% more browse damage than control saplings, suggesting that grass benefited saplings by protecting them from herbivory. However, the negative effect of grass on saplings was far greater; grass-removal trees accrued more than twice the total stem length of control trees. Where wild herbivores were present, saplings were browsed more and produced more new stem growth. Thus, the net effect of wild herbivores was positive, possibly due to the indirect effects of lower competitor tree density in areas accessible to elephants. Additionally, colonization of saplings by symbiotic ants tracked growth patterns, and colonized saplings experienced lower rates of browse damage. These results suggest that savanna tree growth and woody encroachment cannot be predicted by grass cover or herbivore type alone. Rather, tree growth appears to depend on a variety of factors that may be acting together or antagonistically at different stages of the tree's life cycle.

The taphonomic record of Upper Siwalik (Pinjor stage) landscapes in the Pabbi Hills, northern Pakistan, with consideration regarding the preservation of hominin remains

The Pabbi Hills contain a Late Pliocene and Early Pleistocene sequence that was extensively surveyed for fossil remains. Ca. 40,000 specimens from an estimated 1000 individual animals were collected from three types of fossil occurrences ( N=445). Twenty fossil accumulations produced ca. 50% of all fossils found, and over half of all fossil occurrences contained <25 specimens. The largest fossil concentrations were found in silts and fine sands in abandoned and shallow stream channels, and the main agents of fossil accumulation were large predators and streams. The fauna was dominated by herbivores (particularly bovids) >100 kg adult body size. Although buried fossils were generally well preserved, much information was lost after re-exposure by fragmentation and sub-aerial weathering. Comparisons with Miocene Siwalik faunas and environments indicate considerable loss of habitat diversity, fewer types of herbivores, increased herbivore body size and an increased role of predators (notably Pachycrocuta) as accumulating agents. The absence of hominin remains can be attributed to biases towards the preservation of larger animals, the effects of fragmentation and the absence or rarity of stone suitable for making stone tools.

Above-ground herbivory causes rapid and sustained changes in mycorrhizal colonization of grasses

Arbuscular mycorrhizal fungi (AMF) play a vital role in ecosystem functioning. In most grasslands, herbivory by both vertebrate and invertebrate herbivores is common and thus in order to assess herbivore effects on multitrophic-level interactions both should be considered. This study investigated the effects of grazing by rabbit and insect herbivores on root-colonization of grasses by AMF in two lowland grasslands in southern England, UK. A long-term exclosure site was used to provide a temporal assessment in order to elucidate whether any short-term responses to herbivore removal were sustained. Root samples from three grass species at each site were analysed in terms of total mycorrhizal colonization and proportional colonization by individual mycorrhizal structures. Colonization levels were up to 1.6 times greater under moderate levels of rabbit grazing (with summer maxima of 25% and winter minima of 11%) than in intensely grazed swards or fenced plots at both sites. The change was fast (within 8 weeks), consistent throughout the sampled field plots, and temporally sustainable over a 19-year period. There was no significant effect of insect herbivory on total colonization but proportional colonization by different AM structures was affected on some sample dates where vertebrate herbivores had been removed, indicating a slight effect on fungal structure allocation. The results suggest that the type of herbivore and perhaps more importantly the intensity of grazing are key determinants of below-ground effects upon mycorrhizal-host plant symbiosis. The data suggest that the extent of mycorrhizal colonization within grass host plants is strongly influenced by C assimilation and allocation.