On the inability of ants to protect their plant partners and the effect of herbivores on different stages of plant reproduction

Ants co‐occur with herbivorous thrips in several tropical plants, but their interactions are largely unexplored. Should thrips be deterred by ants, a positive effect of ants on plant fitness might be expected. Here, by using an experimental study design with ant‐present and ant‐excluded treatments, we investigated the influence of Camponotus blandus on Pseudophilothrips obscuricornis abundance and herbivory in three extrafloral nectaried species: Banisteriopsis malifolia, B. laevifolia and B. stellaris. In addition, we examined the effect of thrips herbivory on flower set and fruit development and dispersion. Thrips abundance and herbivory were higher on ant‐present stems of B. malifolia and B. laevifolia, where thrips managed to escape from ants by hiding in between clusters of flower buds (thygmotaxis behaviour). In B. stellaris the results were the opposite, as flower bud clusters did not offer hiding places, so thrips were unable to hide from ants; thus both thrips abundance and herbivory were lower on ant‐present stems. Thrips herbivory had no significant effect on flower and fruit set, but samaras (V‐shaped winged fruits of Malpighiaceae) attacked by thrips presented severe distortions and asymmetries. This caused damaged fruits to be dispersed closer to the mother plant, whereas uninjured fruits were dispersed further away. This study is evidence that ant–plant–herbivore systems have variable outcomes depending on the species involved, their behaviour and the plant structure under consideration. Unlike other herbivores, thrips negatively influence the very last stage of plant reproduction. The minute and furtive herbivorous thrips have long been ignored in natural systems, but because of their wide host range, they may be important herbivores even in extrafloral nectaried plants, which are usually fiercely protected by ants.     

Similar responses of insect herbivores to leaf fluctuating asymmetry

Fluctuating asymmetry (FA) represents small, random variation from symmetry and it has been used as an indicator of plant quality and susceptibility to herbivory. In this study, the effects of FA on the responses of distinct herbivore species belonging to several guilds were examined along an environmental gradient in south Florida. This approach was chosen because it relies on a multi-species approach to the study of fluctuating asymmetry and patterns of herbivory between and within plants along an environmental gradient of salinity and plant stress. To examine differences in FA between and within plant communities, seven plant species were investigated. Four of these plants were coastal species and three species occurred in upland communities. Levels of FA were assessed before herbivory and plants were followed for the whole herbivory season in 2006. Coastal plants exhibited significantly higher salt concentration, higher percentage of asymmetric leaves and higher asymmetry levels than upland plants. Herbivore abundance varied widely amongst the seven species studied, but quantitative syntheses of our results indicated significant and positive responses of insect herbivores to leaf asymmetry: insects were 25.11% more abundant on more asymmetric plants and stronger effects of asymmetry were observed for leaf miners compared to gall-formers. As demonstrated by other recent studies, FA might be used as a reliable stress indicator, leading to similar responses of insect herbivores to variation in leaf symmetry.     

Fluctuating asymmetry,leaf thickness and herbivory in <Emphasis Type="Italic">Tibouchina granulosa</Emphasis>: an altitudinal gradient analysis

Gradient of stressful conditions affect plant physiological and morphological traits. Previous studies have shown that plants located at higher altitudes might exhibit higher levels of both fluctuating asymmetry and leaf thickness. Although it is expected that higher fluctuating asymmetry levels should be accompanied by higher leaf consumption by herbivores, lower herbivory could be expected for elevated leaf thickness. Aiming to investigate this contradiction our objective was to determine the effects of altitude on fluctuating asymmetry and leaf thickness, and evaluate the importance of these two morphological traits on herbivory levels of Tibouchina granulosa Cogn. (Melastomatecea) in Brazilian Atlantic Forest. The study was conducted in southern Brazil, along a continuous altitudinal gradient raging from 1275 to 1950 m, where we measured fluctuating asymmetry, leaf thickness and herbivory from leaves of 29 individuals of T. granulosa. There was a positive effect of altitude on both fluctuating asymmetry and leaf thickness but only fluctuating asymmetry was related to herbivore. Our results suggest that as altitude increases plants face more stressful conditions, leading to higher fluctuating asymmetry. This may lead to a higher nutritional quality of leaves and herbivores may use leaf asymmetry as a cue for plant quality. The lack of a relationship between leaf thickness and herbivory gives us evidence that, in the studied location, leaf thickness is not primarily used as plant defense and probably has other functions related, for example, to water, solar radiation, and nutrient stresses. These results may be considered a baseline for the understanding on how altitudinal stress and potential herbivory pressure influence plant populations.     

Perfect is best: low leaf fluctuating asymmetry reduces herbivory by leaf miners

Fluctuating asymmetry (FA) represents small, random variation from symmetry and can be used as an indicator of plant susceptibility to herbivory. We investigated the effects of FA of two oak species, Quercus laevis and Q. geminata, and the responses of three herbivore guilds: leaf miners, gallers, and chewers. To examine differences in FA and herbivory between individuals, 40 leaves from each tree were collected, and FA indices were calculated. To examine differences in FA and herbivory within-individuals, we sampled pairs of mined and unmined leaves for asymmetry measurements. Differences in growth of leaf miners between leaf types were determined by tracing 50 mines of each species on symmetric leaves and asymmetric leaves. Asymmetric leaves contained significantly lower concentrations of tannins and higher concentrations of nitrogen than symmetric leaves for both plant species. Both frequency of asymmetric leaves on plants and levels of asymmetry positively influenced the abundance of Brachys, Stilbosis and other leaf miners, but no significant relationship between asymmetry and herbivory was observed for Acrocercops. Brachys and Stilbosis mines were smaller on asymmetric leaves, but differences in mine survivorship between symmetric and asymmetric leaves were observed only for Stilbosis mines. This study indicated that leaf miners might use leaf FA as a cue to plant quality, although differential survivorship among leaf types was not observed for all species studied. Reasons for the different results between guilds are discussed.     

Sex, secondary compounds and asymmetry. Effects on plant–herbivore interaction in a dioecious shrub

We analysed the links between herbivory, anthraquinone content and developmental instability of leaves in Rhamnus alpinus, taking into account possible effects of sexual dimorphism. The amount of leaf loss caused by herbivores averaged 3%, rarely exceeding 25%. Leaf losses were evenly distributed in the shrubs, with highest variability among leaves of the same shoot, thus hiding possible shrub, sex or population effects. This pattern of herbivory implies a shifting of caterpillars from one leaf to another before consuming all readily available material. We suggest that this behaviour might be triggered by a short-term change in leaf palatability by means of an increase in the production of secondary compounds. Supporting this hypothesis, we have found a higher anthraquinone content in damaged leaves compared with undamaged ones. The leaves of male plants exhibited a higher concentration of anthraquinones than those of females, which contrasts with classic hypotheses. We relate this to the lower rate of biomass increase in males, which should allow them to allocate more resources to defence. Leaves showed fluctuating asymmetry (FA), but we did not find any relationship between the degree of asymmetry and sex, herbivory or anthraquinone content at any level considered. Therefore, FA cannot be considered as an indicator of susceptibility to damage by herbivores or of the ability to induce the production of defensive compounds in R. alpinus.     

Covariation of fluctuating asymmetry, herbivory and chemistry during birch leaf expansion

Fluctuating asymmetry (FA) is used to describe developmental instability in bilateral structures. In trees, high FA of leaves has been assumed to indicate the level of environmental or genetic stress, and for herbivores leaves from such trees have been shown to be in some cases (though not invariably) of higher quality compared to trees with symmetrical leaves. We demonstrated that FA of birch leaves correlated positively with growth rate of leaves, and with the amount of leaf biomass consumed by larvae of the geometrid Epirrita autumnata. Since asymmetry per se cannot define leaf quality for a herbivore, we determined the biochemical compounds which covary with the degree of foliage FA, in order to elucidate relationships between leaf FA, chemistry and herbivory. High foliar FA was characteristic of birches with high initial concentrations, and rapid seasonal decline in the concentrations of gallic acid and hydrolysable tannins, and with rapid seasonal changes in the concentrations of flavonoid-glycosides and sugars. In contrast, leaf FA was not related to concentrations of proanthocyanidins, protein-bound amino acids or soluble phenylalanine, the precursor of proanthocyanidins and proteins with aromatic amino acids. The positive correlation between leaf FA and consumption by E. autumnata was presumably related to the previously demonstrated compensatory consumption of E. autumnata to high concentrations of foliar gallotannins. Furthermore, sugars are well-known feeding stimulants. We propose that the variable results in studies correlating leaf FA and herbivory may stem from variable chemical associations of FA in different plants and of species-specific effects of compounds on insects. Received: 15 July 1999 / Accepted: 24 September 1999     

Fluctuating asymmetry of leaves is a poor indicator of environmental stress and genetic stress by inbreeding in Silene vulgaris

Fluctuating asymmetry (FA) is often used as a measure of developmental instability and has been proposed as an indicator of both environmental and genetic stress. However, the empirical evidence for the effects of stress on FA in plants is inconsistent, and there are few controlled experimental studies. We analyzed different distance- and shape-based measures of the fluctuating asymmetry of the leaves of clonally replicated self- and cross-pollinated lineages of Silene vulgaris (Moench) Garcke (Caryophyllaceae) grown under a control and seven different stress treatments (drought, copper, simulated herbivory, and two levels of nutrient deficiency and of shade). Overall, FA differed among stress treatments, but was not generally higher under stress and even reduced in some treatments. Different measures of FA were only weakly correlated. Inbreeding increased only one measure of leaf FA, and only under high stress intensities. Our findings suggest that in S. vulgaris leaf fluctuating asymmetry does not serve as an indicator of environmental stress or of genetic stress by inbreeding.     

Fire triggers the activity of extrafloral nectaries,but ants fail to protect the plant against herbivores in a neotropical savanna

Herbivores are attracted to young shoots and leaves because of their tender tissues. However, in extrafloral nectaried plants, young leaves also attract patrolling ants, which may chase or prey on herbivores. We examined this scenario in extrafloral nectaried shrubs of Banisteriopsis malifolia resprouting after fire, which promoted both the aseasonal production of leaves and the activity of extrafloral nectaries (EFNs). Results were compared between resprouting (burned) and unburned control plants. The aggressive ant species Camponotus crassus and the herbivorous thrips Pseudophilothrips obscuricornis were respectively rapidly attracted to resprouting plants because of the active EFNs and their less sclerophyllous leaves. The abundance of these insects was almost negligible in the control (unburned) shrubs. Ants failed to protect B. malifolia, as no thrips were preyed upon or injured by ants in resprouting plants. Consequently, on average, 37 % of leaves from resprouting shrubs had necrosis marks. Upon contact with ants, thrips released small liquid droplets from their abdomen, which rapidly displaced ants from the surroundings. This study shows that P. obscuricornis disrupted the facultative mutualism between C. crassus and B. malifolia, since ants received extrafloral nectar from plants, but were unable to deter herbivore thrips.     

Leaf trait variation on Erythroxylum tortuosum (Erythroxylaceae) and its relationship with oviposition preference and stress by a host‐specific leaf miner

It has been suggested that plant physical and chemical traits vary considerably in space and time. Hence, leaf‐mining insects may adjust their oviposition in response to leaf attributes representing high quality. Moreover, herbivorous insects can modify leaf morphology by acting as stressors, increasing, for example, fluctuating asymmetry (FA) levels. Here, we investigate oviposition preference in Agnippe sp.2, a leaf‐mining moth of Erythroxylum tortuosum, in relation to differences in leaf nutritional quality (i.e. levels of water, nitrogen and tannin content), leaf area (i.e. quantity of resource hypothesis) and FA. We also verify whether temporal variation in plant nutritional quality emerges as an alternative hypothesis to explain oviposition distribution in time, and whether this leaf miner is a stress‐causing agent, increasing FA during larval development. Mined leaves and leaves with and without eggs were periodically collected from plants located in a Cerrado fragment in Brazil. In the laboratory, leaf traits were assessed (using image analysis software) and quantified (biochemical analysis) according to the aims previously determined. Oviposition probability did not change in relation to variations in nitrogen, tannins and FA of leaves. However, leaf‐miner females preferred to oviposit on leaves having large areas and low water contents. It was also verified that new leaves of E. tortuosum, which carried most leaf‐miner eggs, presented significantly lower tannins and greater levels of nitrogen and water than old leaves. The oviposition choice exhibited by leaf miners was found to be non‐random because they appear to use resource quantity and water content as cues as where to lay their eggs. The temporal variation of plant nutritional quality is likely to influence the time of leaf‐miner oviposition; and leaf FA was not increased during larval feeding, suggesting that these herbivores do not cause variations in FA levels.     

Consequences of herbivory in the mountain birch (Betula pubescens ssp tortuosa): importance of the functional organization of the tree

Summary Three types of experiments indicate that the functional organization of the mountain birch may influence the ways in which the tree responds to simulated or natural herbivory. The first experiment showed that herbivory to both short and long shoot leaves affects plant development but, because growth largely proceeds by resources of the previous year, is manifested only in the year following the damage. The second experiment showed that even partial damage to a single long shoot leaf caused the axillary bud of that leaf to produce a shorter shoot the next year. Therefore, the value of a leaf depends also on the organ which it is subtending. In the third experiment we manipulated the apical dominance of shoots in ramets and caused improvement to leaf quality in extant shoots. Ramets within a tree responded individually, probably mediated by disturbance of the hormonal control because removal of apical buds elicited the response although removal of the same number of basal buds did not. Induced amelioration is a different response to induced resistance. The two responses are triggered by different cues and may occur in the same plant. By altering hormonal balance of shoots it is potentially possible for herbivores to induce amelioration of food quality. The ways in which herbivory is simulated may explain variability of results obtained when herbivory-induced responses in plants have been studied.     

Herbivore effects on developmental instability and fecundity of holm oaks

Plants are able to compensate for loss of tissue due to herbivores at a variety of spatial and temporal scales, masking detrimental effects of herbivory on plant fitness at these scales. The stressing effect of herbivory could also produce instability in the development of plant modules, and measures of such instability may reflect the fitness consequences of herbivory if instability is related to components of plant fitness. We analyse the relationships between herbivory, developmental instability and production of female flowers and fruits of holm oak Quercus ilex trees by means of herbivore removal experiments. Removal of leaf herbivores reduced herbivory rates at the tree level, but had no effect on mean production of female flowers or mature fruits, whereas herbivory tended to enhance flower production and had no effect on fruit abortion at the shoot level. Differences in herbivory levels between shoots of the same branch did not affect the size and fluctuating asymmetry of intact leaves. These results indicate compensation for herbivory at the tree level and over-compensation at the shoot level in terms of allocation of resources to female flower production. Removal of insect herbivores produced an increase in the mean developmental instability of leaves at the tree level in the year following the insecticide treatment, and there was a direct relationship between herbivory rates in the current year and leaf fluctuating asymmetry the following year irrespective of herbivore removal treatment. Finally, the production of pistillate flowers and fruits by trees was inversely related to the mean fluctuating asymmetry of leaves growing the same year. Leaf fluctuating asymmetry was thus an estimator of the stressing effects of herbivory on adult trees, an effect that was delayed to the following year. As leaf fluctuating asymmetry was also related to tree fecundity, asymmetry levels provided a sensitive measure of plant performance under conditions of compensatory responses to herbivory.     

Do defoliating insects distinguish between symmetric and asymmetric leaves within a plant?

1. Plants represent a highly heterogeneous resource for herbivores. One dimension of this heterogeneity is reflected by the within‐plant variation in the leaf fluctuating asymmetry (FA), i.e. in the magnitude of the random deviations from the symmetry in leaf shape. 2. This study is the first to test experimentally the hypothesis that variation in the quality of individual leaves for defoliating insects (11 species) within a plant (seven tree and shrub species) is associated with the FA of these leaves. 3. It was demonstrated that specialist defoliators generally distinguish between nearly symmetric (low FA) and highly asymmetric (high FA) leaves, but do not distinguish between discs cut from these leaves. Low‐FA leaves of Salix caprea, Salix myrsinifolia and Populus tremula were of better quality for insects than high‐FA leaves, as demonstrated by both preference tests and performance trials. By contrast, high‐FA leaves of Betula pubescens were of better quality for insects than low‐FA leaves, whereas insects feeding on Alnus incana showed similar responses to high‐ and low‐FA leaves. 4. It is concluded that insect herbivores can distinguish between leaves with high and low FA, and that FA may be associated with the quality of an individual leaf for insects, although the direction and strength of the effect of leaf FA on insect preference and performance vary among study systems. The ecological significance of substantial within‐plant variation in leaf FA remains to be explored.     

Fluctuating asymmetry and herbivory in two ontogenetical stages of Chamaecrista semaphora in restored and natural environments

Reintroduced environments represent stressful conditions to plants that can be observed in different ways. We evaluated the relationships between fluctuating asymmetry (FA), herbivory, and plant ontogeny of Chamaecrista semaphora (Fabaceae) under natural and restored habitat conditions. The patterns of leaf FA and herbivory by folivorous insects (chewing) on saplings and mature plants in each habitat were determined. No relationship was found between FA and herbivory on the two ontogenetic stages in both environments, suggesting that FA did not represent an indicator of stress. The frequency and amount of leaf area removed by folivores were higher in saplings compared to adult plants under the natural habitat, while the opposite trend was observed on restored habitat for adult plants. The restored habitat did not represent an environmental stress condition to C. semaphora, indicating that this endemic plant may represent a good candidate to restoration programs in harsh environments. However, we observed great differences in leaf FA and herbivory among individuals within habitats. Knowledge on plant quality, competition, physiology, and interactions with natural enemies are highly needed to support long lasting programmes on restoration of harsh environments.     

The response of leaf resin to artificial herbivory in Eriodictyon californicum

Herbivore damage induces the production of defensive chemicals in many plant species. However, defensive chemicals sometimes have functions other than protection from herbivores, and these chemicals may respond to hervibory differentialy than those which are primarily defensive. A well-studied group of leaf constituents with multiple functions is the phenolic leaf resins, which protect leaves from herbivores, UV radiation, and possibly excess water loss. The effects of herbivory on phenolic leaf resins were investigated in the chapparral shrub Eriodictyon californicum by artificially damaging leaves during the growing season and subsequently measuring resin content and composition. We found that (i) resin content declined in leaves damaged by artificial herbivory; (ii) resin declined (at the P < 0.1 level) in undamaged leaves present on the same plant as those heavily damaged; and (iii) resin composition, as measured by the ratio of the major components, was unaffected by artificial herbivory.     

Explaining differential herbivory in sun and shade: the case of Aristotelia chilensis saplings

Differential herbivory in contrasting environments is commonly explained by differences in plant traits. When several plant traits are considered, separate correlation analyses between herbivory and candidate traits are typically conducted. This makes it difficult to discern which trait best explain the herbivory patterns, or to avoid spurious inferences due to correlated characters. Aristotelia chilensis saplings sustain greater herbivory in shaded environments than in open habitats. We measured alkaloids, phenolics, trichomes, leaf thickness and water content in the same plants sampled for herbivory. We conducted a multiple regression analysis to estimate the relationship between herbivory and each plant trait accounting for the effect of correlated traits, thus identifying which trait(s) better explain(s) the differential herbivory on A. chilensis. We also estimated insect abundance in both light environments. Palatability bioassays tested whether leaf consumption by the main herbivore on A. chilensis was consistent with field herbivory patterns. Overall insect abundance was similar in open and shaded environments. While saplings in open environments had thicker leaves, lower leaf water content, and higher concentration of alkaloids and phenolics, no difference in trichome density was detected. The multiple regression analysis showed that leaf thickness was the only trait significantly associated with herbivory. Thicker leaves received less damage by herbivores. Sawfly larvae consumed more leaf tissue when fed on shade leaves. This result is consistent with field herbivory and, together with results of insect abundance, renders unlikely that the differential herbivory in A. chilensis was due to greater herbivory pressure in open habitats.     

Friend or foe?: a plant's induced response to an omnivore

Omnivorous natural enemies of herbivores consume plant-based resources and may elicit induced resistance in their host plant. A greater induction threshold for damage produced by omnivorous predators than for strict herbivores might be expected if omnivore performance is enhanced on noninduced plants, allowing them to reduce future levels of herbivory. Currently, it is not known if a plant responds to feeding by omnivorous predators and by herbivores similarly. To examine this question, we chose herbivore and omnivore species that produce the same kind of quantifiable damage to cotton leaves, enabling us to control statistically for the intensity of plant damage, and ask whether plant responses differed depending on the identity of the damaging species. We first compared changes in plant peroxidase activity, gossypol gland number and density, and leaf area in response to feeding by the spider mite Tetranychus turkestani (Ugarov and Nikolski) (an herbivore) and by one of the mite's principal natural enemies, the western flower thrips Frankliniella occidentalis (Pergande) (an omnivore). Both species increased the activity of peroxidase, but when we controlled for the amount of damage, the peroxidase activity of mite-damaged plants was higher than that of thrips-damaged plants. We also found that thrips, but not spider mites, increased the density of gossypol glands in the second true leaf. In a second experiment we included an additional herbivore, the bean thrips Caliothrips fasciatus (Pergande), to see if the different responses of cotton to thrips and mite herbivory we first observed were attributable to differences in trophic function (herbivore versus omnivore) or to other differences in feeding generated by thrips versus mites. Cotton plants exhibited the same pattern of induced responses (elevated peroxidase, increased number of glands, reduced leaf area) to herbivory generated by the bean thrips (an herbivore) and western flower thrips (an omnivore), suggesting that trophic function was not a key determinant of plant response. Thrips-damaged plants again showed a significantly higher density of gossypol glands than did mite-damaged plants. Overall, our results suggest that (1) an omnivorous predator systemically induces resistance traits in cotton and (2) whereas there is evidence of taxonomic specificity (thrips versus mites), there is little support for trophic specificity (herbivorous thrips versus omnivorous thrips) in the elicitation of induced responses.     

Does insect herbivory on oak depend on the diversity of tree stands?

Studies on the effects of plant diversity on insect herbivory have produced conflicting results. Plant diversity has been reported to cause positive and negative responses of herbivores. Explanations for these conflicting responses include not only various population-level processes but also changes in plant quality that lead to changes in herbivore performance. In a tree diversity experiment, we investigated the effects of tree diversity on insect herbivory on oak in general and whether the effects of tree diversity on herbivore damage are reflected by the performance (leaf consumption, growth) of the generalist herbivore Lymantria dispar. Our study showed that the feeding damage caused by naturally occurring herbivores on oak trees decreased with increasing diversity of tree stands. The performance of L. dispar on oak leaves was not affected by tree diversity, neither in field nor laboratory experiments. Our results can be explained by the various processes behind the hypothesis of associational resistance.     

The effects of drought and herbivory on plant–herbivore interactions across 16 soybean genotypes in a field experiment

相似文献   

The Invasive Plant Alternanthera philoxeroides Was Suppressed More Intensively than Its Native Congener by a Native Generalist: Implications for the Biotic Resistance Hypothesis

Prior studies on preferences of native herbivores for native or exotic plants have tested both the enemy release hypothesis and the biotic resistance hypothesis and have reported inconsistent results. The different levels of resistance of native and exotic plants to native herbivores could resolve this controversy, but little attention has been paid to this issue. In this study, we investigated population performance, photosynthesis, leaf nitrogen concentration, and the constitutive and induced resistances of the successful invasive plant, Alternanthera philoxeroides, and its native congener, Alternanthera sessilis, in the presence of three population densities of the grasshopper, Atractomorpha sinensis. When the grasshopper was absent, leaf biomass, total biomass, photosynthesis, and leaf nitrogen concentration of A. philoxeroides were higher than those of A. sessilis. However, the morphological and physiological performances of A. philoxeroides were all decreased more intensively than A. sessilis after herbivory by grasshoppers. Especially as the concentrations of constitutive lignin and cellulose in leaf of A. philoxeroides were higher than A. sessilis, A. philoxeroides exhibited increased leaf lignin concentration to reduce its palatability only at severe herbivore load, whereas, leaf lignin, cellulose, and polyphenolic concentrations of A. sessilis all increased with increasing herbivory pressure, and cellulose and polyphenolic concentrations were higher in A. sessilis than in A. philoxeroides after herbivory. Our study indicated that the capability of the invasive plant to respond to native insect damage was lower than the native plant, and the invasive plant was suppressed more intensively than its native congener by the native insect. Our results support the biotic resistance hypothesis and suggest that native herbivores can constrain the abundance and reduce the adverse effects of invasive species.     

Cascading effects of induced terrestrial plant defences on aquatic and terrestrial ecosystem function

Herbivores induce plants to undergo diverse processes that minimize costs to the plant, such as producing defences to deter herbivory or reallocating limited resources to inaccessible portions of the plant. Yet most plant tissue is consumed by decomposers, not herbivores, and these defensive processes aimed to deter herbivores may alter plant tissue even after detachment from the plant. All consumers value nutrients, but plants also require these nutrients for primary functions and defensive processes. We experimentally simulated herbivory with and without nutrient additions on red alder (Alnus rubra), which supplies the majority of leaf litter for many rivers in western North America. Simulated herbivory induced a defence response with cascading effects: terrestrial herbivores and aquatic decomposers fed less on leaves from stressed trees. This effect was context dependent: leaves from fertilized-only trees decomposed most rapidly while leaves from fertilized trees receiving the herbivory treatment decomposed least, suggesting plants funnelled a nutritionally valuable resource into enhanced defence. One component of the defence response was a decrease in leaf nitrogen leading to elevated carbon : nitrogen. Aquatic decomposers prefer leaves naturally low in C : N and this altered nutrient profile largely explains the lower rate of aquatic decomposition. Furthermore, terrestrial soil decomposers were unaffected by either treatment but did show a preference for local and nitrogen-rich leaves. Our study illustrates the ecological implications of terrestrial herbivory and these findings demonstrate that the effects of selection caused by terrestrial herbivory in one ecosystem can indirectly shape the structure of other ecosystems through ecological fluxes across boundaries.