Amount Of Herbivory Research Articles

Effects of varying types and amounts of herbivory and nutrient enrichment on a tropicalizing seagrass meadow

Climate change is impacting marine ecosystem community dynamics on a global scale. While many have assessed direct effects of climate change, indirect effects on marine ecosystems produced by biotic interactions remain poorly understood. For example, warming-induced range expansions and increased consumption rates of herbivores can lead to significant and unexpected changes in seagrass-dominated ecosystems. To better understand the threats tropicalization presents for the functioning of turtlegrass (Thalassia testudinum) meadows, we focused on the extensive turtlegrass beds of St. Joseph Bay, Florida in the northern Gulf of Mexico, a location with increasing numbers of tropically-associated green turtles. Our goals were to investigate experimentally how different grazing rates (natural and simulated),including high levels reflective of green turtle herbivory, coupled with nutrient supply, might alter turtlegrass structure and functioning in a higher latitude, subtropical turtlegrass meadow. We found that 4 months of varying levels of herbivory did not affect turtlegrass productivity, while 7 months of herbivory reduced percent cover, and 10 months reduced shoot density. Nutrient additions had few important effects. Ten months into the study, a massive recruitment of the herbivorous sea urchin (Lytechinus variegatus), whose densities reached 19 urchins/m2 completely overgrazed our study area and a large portion of the lush turtlegrass meadows of St. Joseph Bay. While local turtlegrass overgrazing had been previously noted at these urchin densities, a total loss of seagrass in such a large area has rarely ever been recorded. Overgrazing of the kind we observed, likely a result of both urchin and increasing green turtle grazing, can result in the loss of many key ecosystem services. As tropicalization continues, understanding how changes in biotic interactions, such as increased herbivory, affect higher latitude seagrass meadows will be necessary for their proper management and conservation.

Bottom-up control of geographic variation in insect herbivory on wild cotton (Gossypium hirsutum) by plant defenses and climate.

The occurrence and amount of herbivory are shaped by bottom-up forces, primarily plant traits (e.g., defenses), and by abiotic factors. Addressing these concurrent effects in a spatial context has been useful in efforts to understand the mechanisms governing variation in plant-herbivore interactions. Still, few studies have evaluated the simultaneous influence of multiple sources of bottom-up variation on spatial variation in herbivory. We tested to what extent chemical (phenolics, production of terpenoid glands) and physical (pubescence) defensive plant traits and climatic factors are associated with variation in herbivory by leaf-chewing insects across populations of wild cotton (Gossypium hirsutum). We found substantial population variation in cotton leaf defenses and insect leaf herbivory. Leaf pubescence, but not gossypol gland density or phenolic content, was significantly negatively associated with herbivory by leaf-chewing insects. In addition, there were direct effects of climate on defenses and herbivory, with leaf pubescence increasing toward drier conditions and leaf damage increasing toward wetter and cooler conditions. There was no evidence, however, of indirect effects (via plant defenses) of climate on herbivory. These results suggest thatspatial variation in insect herbivory on wild G. hirsutum is predominantly driven by concurrent and independent influences of population variation in leaf pubescence and climatic factors.

Insect herbivory on snow gum (Eucalyptus pauciflora, Myrtaceae) saplings near the alpine treeline: the influence of local- and landscape-scale processes

The distribution and abundance of plant species in high mountain ecosystems are thought to depend largely on abiotic factors that play out at both landscape scales (e.g. steep environmental gradients affected by increasing elevation) and local scales (e.g. changes in topography, aspect and canopy cover). However, relatively little attention has been paid to biotic interactions, and how these might also change with landscape-wide and local factors. Ecological interactions between plants and insect herbivores are likely to alter species performance and affect local abundance, but their role in the Australian Alps remains largely unexplored. Here, we examine the prediction that the amount of herbivory on saplings of the dominant high elevation tree, snow gum Eucalyptus pauciflora Sieb. ex Spreng. (Myrtaceae), are lower at higher elevation because of increasing environmental stress. Using a reciprocal transplant experiment, we tested the prediction that origin of seed (low, mid, high elevation) has less effect on insect herbivory than environmentally-driven changes in plant morphology (height, leaf thickness, specific leaf area). Across all mountains studied, herbivory was best explained by a combination of plant height, canopy openness, leaf thickness and elevation, but not seed origin. This study highlights the individuality of each mountain environment, at landscape and local scales, as well as the complexity of relationships between environmental change, plants and insects. Given the factors that best explain herbivory across mountains, herbivory may decrease with decreasing productivity associated with increasing elevation, a trend in broad agreement with hypotheses associating leaf area loss to the availability of resources and plant vigour.

An equation for determining percentage of herbivory on Pinguicula moranensis ' A correction

Recently Alcalá et al. (2010) explored the potentially defensive function of sticky traps in Pin- guicula moranensis. Specifically, the authors assessed the defensive role of glandular trichomes in the interaction between P. moranensis and its insect herbivores. Alcalá et al. (2010) offered a unique digital photography tool and a method for determining the amount of herbivory. To create a baseline level of insect herbivory the authors developed an equation to determine the percentage of leaf herbivory. Unfortunately, the equation published in the article contained an error. The goal of this article is to offer a correction to the error.

Assessing the latitudinal gradient in herbivory

AbstractPlant–herbivore interactions occur in all ecosystems and provide a major avenue for energy flow to higher trophic levels. A long‐standing hypothesis to explain the latitudinal gradient in species diversity proposes that the relatively stable and frost‐free climate of the tropics should lead to more intense biotic interactions in tropical compared with temperate environments, giving rise to a greater diversity of plants and herbivores. Herbivory rates have been compared across latitudes to test this biotic interactions hypothesis, with herbivory typically being measured from observable leaf damage. However, we argue that a measure of percentage leaf damage alone does not straightforwardly reflect the cost of herbivory to the plant, and on its own does not constitute an appropriate test of the biotic interactions hypothesis. For a given amount of herbivory, the impact of herbivory is dependent upon many factors, such as the construction cost of the leaf, the growth and replacement rates and leaf life span. We investigate the latitudinal gradient in herbivory by analysing a large dataset of herbivory rates for 452 tree species and separating the species into those with short and long leaf life spans. We show that annual herbivory rates tend to be greater at lower latitudes for evergreen species (which have long‐lived leaves), but no trend in herbivory rate with latitude was found for species with short leaf life spans. Phylogenetic least squares regression assuming Ornstein‐Uhlenbeck processes also showed a negative effect of latitude on herbivory rate for evergreen trees, but we caution that viewing herbivory as a species trait is problematic. An integrative approach that incorporates leaf life span, as well as the costs of investment in growth and potential costs of losing leaf tissue, is needed to further our understanding of the ecological and evolutionary dynamics of herbivory.

Plant choice, herbivory and weight gain of wood crickets under the risk of predation

Predators can indirectly reduce herbivory by killing herbivores. In addition, predation risk can influence the feeding rate and feeding location of herbivores. Herbivores are expected to avoid plants currently occupied by a predator. Consequently, less herbivory is expected on plants bearing fresh predator cues. We examined whether wood crickets, Nemobius sylvestris Bosc (Orthoptera: Gryllidae), avoided plants bearing the chemical cues of nursery web spiders, Pisaura mirabilis Clerck (Araneae: Pisauridae), or red wood ants, Formica rufa L. (Hymenoptera: Formicidae). We conducted a series of behavioural experiments, in which crickets had the choice between a plant with spider or ant cues vs. a control plant, a plant with spider cues vs. a plant with ant cues, or two control plants. For all plants, we quantified leaf damage and the position and weight change in the crickets. Crickets avoided plants with spider cues. In contrast, ant cues did not significantly deter crickets. The herbivory pattern among the plants reflected the plant choice of the crickets. However, net herbivory was not affected by the presence of predator cues. Thus, our results suggest that spider cues affect feeding location rather than the total amount of herbivory.

Effect of fragmentation on predation pressure of insect herbivores in a north temperate deciduous forest ecosystem

1. Forest fragmentation affects many ecosystem processes by spatially altering relationships among organisms. Herbivory by arthropods is an important ecosystem processes in forests that fragmentation alters by changing relationships among herbivores, their predators, and their hosts. The relative importance of these factors remains unclear.2. It was tested whether the exclusion of vertebrate predators affected the arthropod abundance or amounts of herbivory in a fragmented, deciduous forest landscape in southern Quebec. Differences in the abundance of arthropod herbivores and amounts of herbivory in forest patches with different landscape characteristics (small isolated patches versus large connected ones), on sugar maple saplings with or without exclosures that restricted access by large vertebrate predators were measured.3. Saplings protected from predators with exclosures had greater abundances of all arthropods (herbivores and invertebrate predators) than those without, indicating potential top‐down effects of vertebrate predators on arthropods. Analysis of effect sizes between exclosure treatments and controls suggests the magnitude of predation effects may be affected by fragmentation.4. Strong top‐down effects of predators on arthropods, and weak effects of fragmentation on predation or amounts of herbivory were found. As a result, herbivory may be regulated by factors other than vertebrate predation in this system.

Selective Herbivory by the Desert Woodrat (Neotoma lepida) on Joshua Trees (Yucca brevifolia)

We studied herbivory by the desert woodrat (Neotoma lepida) on Joshua trees (Yucca brevifolia) in the Mojave Desert to determine whether N. lepida fed selectively based on leaf nitrogen content. We measured leaf nitrogen content and the location and amount of herbivory by woodrats on Y. brevifolia trees in southwestern Utah, USA. Neotoma lepida removed the outer tips of leaves (⅓ to ⅔ of total leaf length) but left leaf bases, which had lower nitrogen content, uneaten. Herbivory by N. lepida also was concentrated on rosettes that were oriented south, and these had significantly higher nitrogen content than rosettes that were oriented north. Finally, N. lepida fed more on trees that had higher mean leaf nitrogen contents. Thus, N. lepida selectively foraged among leaf parts, among rosettes of leaves, and among trees of Y. brevifolia, and disproportionate foraging was correlated with nitrogen content of leaves.

Indirect defense in a highly specific ant–plant mutualism

Although associations between myrmecophytes and their plant ants are recognized as a particularly effective form of protective mutualism, their functioning remains incompletely understood. This field study examined the ant-plant Hirtella physophora and its obligate ant associate Allomerus decemarticulatus. We formulated two hypotheses on the highly specific nature of this association: (1) Ant presence should be correlated with a marked reduction in the amount of herbivory on the plant foliage; (2) ant activity should be consistent with the "optimal defense" theory predicting that the most vulnerable and valuable parts of the plant are the best defended. We validated the first hypothesis by demonstrating that for ant-excluded plants, expanding leaves, but also newly matured ones in the long term, suffered significantly more herbivore damage than ant-inhabited plants. We showed that A. decemarticulatus workers represent both constitutive and inducible defenses for their host, by patrolling its foliage and rapidly recruiting nestmates to foliar wounds. On examining how these activities change according to the leaves' developmental stage, we found that the number of patrolling ants dramatically decreased as the leaves matured, while leaf wounds induced ant recruitment regardless of the leaf's age. The resulting level of these indirect defenses was roughly proportional to leaf vulnerability and value during its development, thus validating our second hypothesis predicting optimal protection. This led us to discuss the factors influencing ant activity on the plant's surface. Our study emphasizes the importance of studying both the constitutive and inducible components of indirect defense when evaluating its efficacy and optimality.

Patterns of host damage by the cabbage tree monophage Epiphryne verriculata Feld (Lepidoptera: Geometridae) across urban, rural and native forest habitats

Little is known about the persistence of host-specialised insect herbivores on their host plants in highly modifi ed urban and rural landscapes, and the ecological processes driving their abundance and distribution in these landscapes. We surveyed cabbage trees (Cordyline australis) at 13 sites encompassing a variety of habitat types located across a highly modifi ed landscape, the Canterbury Plains, for damage by the larvae of the endemic monophagous geometrid moth, Epiphryne verriculata. We recorded the relative amount of E. verriculata herbivory on cabbage tree crowns and measured a number of environmental variables we expected would explain variation in this herbivory. While E. verriculata occurred at all sampled sites and on 244 of the 257 sampled trees, there was substantial variation among trees in the amount of herbivory. Epiphryne verriculata herbivory per tree was higher on adult trees than seedlings and was highest, unexpectedly, in areas of low con specific density within 25 m. We found no effects on herbivory of substrate nor the presence of a skirt of dead leaves, which has been suggested to be an important refuge for adult E. verriculata. The amount of herbivory differed among habitat types, with trees in native forest sites having signifi cantly higher amounts of damage than those in urban and rural sites. This pattern has been found in other New Zealand insect herbivore systems, and may represent a general pattern in the New Zealand insect herbivore fauna. We predict that this pattern is not a result of dispersal limitation in E. verriculata, but rather ecological processes increasing larval mortality, and perhaps decreasing adult fecundity and oviposition, within urban and rural habitats.

Beyond the compensatory continuum: environmental resource levels and plant tolerance of herbivory

The impact that herbivore damage has on plant fitness depends on the environmental conditions in which the plant is growing. It has long been assumed that a plant's tolerance of herbivory should be greater in low‐stress, resource‐rich environments, and this assumption has been formalized in what has become known as the compensatory continuum hypothesis (CCH). Despite the widespread acceptance of the CCH, recently accumulating results from numerous studies relating resource levels to tolerance of herbivory show that the relationship is not as simple as this hypothesis predicts. In fact, plants have often been found to be less tolerant of a given amount of herbivory in resource‐rich environments than they are of the same amount of herbivory in resource‐poor environments. In this article, we present a new model, the limiting resource model (LRM), that can more reliably explain the range of observed effects of resource levels on tolerance. The main advance of this model is that it specifically considers which factors are limiting plant fitness and which resources are affected by particular herbivores. The LRM is presented in a general and flexible form as a flowchart with seven pathways to three potential outcomes: greater tolerance, equal tolerance, or lower tolerance in low‐ vs high‐resource environments. We then review a specific example to illustrate each of these seven pathways with a study from the published literature. We finish with a description of four general criteria to direct the design of future studies to test the predictions of the LRM.

Multitrophic Effects of Elevated Atmospheric CO<SUB>2</SUB> on Understory Plant and Arthropod Communities

Rising levels of atmospheric [CO2] will directly affect the responses and community composition of plants. However, few studies have examined how these changes to plant communities will alter insect communities that rely on them. Here, we report on a study that examined the community-level responses of plants, herbivores, detritivores, predators, parasitoids, and omnivores to increased [CO2] at a Free Air Carbon Enrichment (FACE) facility at Oak Ridge National Laboratory. We found that aboveground net primary productivity for the five dominant plant species in the understory community, C:N ratios of leaf tissue for four of the five dominant understory taxa, amounts of herbivory, and arthropod abundance and richness across all trophic groups did not differ between ambient and elevated CO2 plots. Abundance and richness of particular trophic groups were higher in ambient than in elevated CO2 plots. There were also strong temporal effects on community composition, but no distinct treatment effects. These results, although preliminary, suggest that community-level responses to future atmospheric [CO2] are likely to be species- and trophic-group specific.

Variation in Herbivore Damage to Invasive and Native Woody Plant Species in Open Forest Vegetation on Mahé, Seychelles

Enemy release of introduced plants and variation in herbivore pressure in relation to community diversity are presently discussed as factors that affect plant species invasiveness or habitat invasibility. So far few data are available on this topic and the results are inconclusive. We compared leaf herbivory between native and invasive woody plants on Mahe, the main island of the tropical Seychelles. We further investigated variation in leaf herbivory on three abundant invasive species along an altitudinal gradient (50–550 m a.s.l.). The median percentage of leaves affected by herbivores was significantly higher in native species (50%) than in invasive species (27%). In addition, the species suffering from the highest leaf area loss were native to the Seychelles. These results are consistent with the enemy release hypothesis (ERH). While the invasive species showed significant and mostly consistent variation in the amount of leaf damage between sites, this variation was not related to general altitudinal trends in diversity but rather to local variation in habitat structure and diversity. Our results indicate that in the Seychelles invasive woody plants profit from herbivore release relative to the native species and that the amount of herbivory, and therefore its effect on species invasiveness or habitat invasibility, may be dependent on local community structure and composition.

Wooded habitat edges as refugia from microtine herbivory in tallgrass prairies

Meadow voles, Microtus pennsylvanicus, affect the species composition, distribution, and succession of plants in grassland ecosystems, but the effects of voles on herbaceous plants when grasslands are bordered by wooded edges is not known. We investigated the impact of wooded edges on vole distribution and herbivory of relatively palatable and unpalatable native prairie plant species by studying five reconstructed tallgrass prairies with wooded edges in central Iowa. A 50×50 m trapping grid at each site was established to determine the proportion of voles captured at various distances from the edge. We found that meadow voles were less abundant at wooded edges and, in general, increased in number toward the prairie interior. Seedlings of purple prairie clover (Dalea purpurea) and Illinois bundleflower (Desmanthus illinoensis), a relatively palatable and unpalatable species, respectively, were transplanted onto simulated gopher mounds 2, 5, 10, 20 and 30 m from the edge. The number of plants grazed per species per mound was determined 1 week and 4 weeks after planting. The amount of herbivory on both species was significantly different by distance, with fewer plants eaten 2 m from the edge. Interestingly, the amount of herbivory on relatively unpalatable plants did not differ from more palatable plants. Herbivory on both plant species also varied by site, such that sites with lower vole density tended to have lower amounts of herbivory. These results indicate that wooded edges do have an effect on meadow vole distribution and native prairie seedling herbivory. Because voles avoid wooded edges, seedlings of any species may experience a small refuge from herbivory along wooded edges.

Palatability of weeds from different European origins to the slugs Deroceras reticulatum Müller and Arion lusitanicus Mabille

Abstract As part of a study on the significance of seed provenances in schemes to enhance biodiversity in agricultural habitats, juvenile plants of Cichorium intybus, Daucus carota, Leucanthemum vulgare and Silene alba of different European origins were exposed to grazing by two slug species, Deroceras reticulatum and Arion lusitanicus . Living plants were offered in trays, either in a glasshouse ( Deroceras ) or outdoors ( Arion ). The amount of herbivory was origin-dependent, with higher losses for all four species from German and Hungarian provenances compared with English and Swiss plants. The main trend was similar for both slug species except in the case of Daucus , and there was a significant ‘origin × plant species’ interaction. We found strong correlations between provenance-specific herbivory and certain climatic characteristics of the corresponding regions, i.e. winter minimum temperatures, and dryness in spring and late summer, which are crucial for the development of slugs. The results can be interpreted in terms of a SW-NE European climatic gradient and may be a consequence of differences in the need for plant defences against herbivory by slugs. Additionally, the data on palatability were compared with susceptibility towards two parasites which occurred in a field experiment, a leaf miner on Leucanthemum vulgare and a rust fungus on Silene alba . While specific leaf mining frequencies on Leucanthemum contrasted with the palatability of the different provenances to slugs, the rust infection on Silene was low on local and German plants, and higher on the more distant provenances from England and Hungary.

Factors affecting floral herbivory in a limestone grassland

The amount of herbivore damage to the petals of 41 species of herbaceous plant was surveyed from April to September in a limestone grassland in central England. Damage was recorded as the percentage of the petal area removed. Most damage was caused by invertebrates, particularly slugs. The amount of invertebrate damage differed significantly between plant species and with time of year. The mean damage across all species was only 2 %, ranging from an average of 0 % in Galium sterneri to 8 % in Primula vulgaris. In most species, less than a quarter of flowers received any damage, so those that were damaged were often severely affected. Species flowering early or late in the season received more damage, possibly because of greater slug activity. Hypotheses to explain the inter-specific variation in the amount of herbivory were examined by testing for correlations with a range of plant variables. No correlations with flower-stem length, flower-stem thickness or the longevity of flowers were apparent. The amount of petal damage correlated strongly with flower size and petal thickness. This appeared to result from the prevalence of large-flowered species early and late in the season rather than from a preference for flower size and petal thickness per se. The evolutionary significance of floral herbivory is discussed.

Effects of simulated N deposition on understorey vegetation of a boreal coniferous forest

1. We report the short‐term effects of simulated nitrogen (N) deposition on the understorey of a boreal forest in northern Sweden. Doses of 15N double‐labelled NH4NO3 (0·5, 12·5, 25·0 and 50·0 kg N ha–1) were applied to 1 m2 plots in the summer of 1995 and plants were harvested the following autumn. 2. No significant treatment effects were found in either above‐ or below‐ground biomass which was distributed as follows: the ericaceous shrub Vaccinium myrtillus contributed 76%, the grass Deschampsia flexuosa 4%, and the bryophytes Dicranum majus and Pleurozium schreberi 20%. 3. The recovery of applied N in these species was 24, 27, 27 and 32% of the 0·5, 12·5, 25·0 and 50·0 kg N ha–1 applications, respectively, and thus the recovery increased with the N dose. 4. In the 0·5 kg N ha–1 treated plots, the highest concentrations of fertilizer‐derived 15N were found in the bryophytes, while in plots given the three higher N applications, leaves of D. flexuosa had the highest concentrations. 5. N application resulted in elevated concentrations of free amino acid N, which indicate increased storage of N in plant tissues. Furthermore, the N application resulted in increased damage to V. myrtillus by natural enemies. The severity of disease caused by two foliar parasitic fungi showed a clear numerical response to N treatment, as did the amount of herbivory as a result of Lepidoptera larvae.

Morphological Development of 2 Warm-Season Grasses in the Nebraska Sandhills

Morphological development of grasses has numerous implications to rangeland management including the timing and amount of herbivory. The objective of this study was to quantify the developmental morphology of prairie sandreed [Calamovilfa longifolia (Hook.) Scribn.] and sand bluestem [Andropogon gerardii var. paucipilus (Nash) Fern.] tiller populations. Tiller populations of these 2 grasses were studied for 2 years in the Nebraska Sandhills. Plant development was evaluated using a growth staging system which quantifies the development of tiller populations. A morphological growth index for each species was calculated from either the weighted average of tiller numbers reported as mean stage count (MSC) or tiller weight reported as mean stage weight (MSW) and correlated with the independent variables of growing degree days (GDD) and day of year (DOY). Correlation coefficients with the independent variables were greater than 0.97 for MSC and MSW within years and greater than 0.90 between years. Greater rainfall and warmer temperatures in 1991 increased the number of tillers in the more advanced morphological stages in prairie sandreed, but tiller weight rather than tiller number increased in more advanced stages of sand bluestem. A majority of the harvested tillers were vegetative throughout the sampling period but by the end of the growing season, a wide range of morphological stages were present. The use of grazing to prevent the formation of culmed tillers in these grasses may be unnecessary because of the high proportion of vegetative tillers and the wide range of morphological stages available for selection by livestock.

Interspecific and Intraspecific Interactions Via Plant Responses to Folivory: An Experimental Field Test

I tested the hypothesis that phytophagous insect species compete interspecifically on shared host plants by inducing chemical, physical, and phenological changes in the plant that either directly reduce insect growth and survival or indirectly alter attack by natural enemies. I manipulated levels of simulated folivory on branches within eight trees of Quercus emoryi in a complete randomized block design. Survival and causes of mortality, including attack by natural enemies, of a dominant leafminer, Cameraria sp. nov., were monitored over two growing seasons. Survival varied significantly among trees but not among treatments. Causes of mortality also varied significantly among trees. Death from premature leaf abscission increased significantly with increasing levels of branch damage, while mortality from other causes, including death from bacterial and fungal attack, declined significantly with increasing levels of damage. However, neither of these changes in mortality was sufficient to cause changes in overall survival. Leaf damage did not influence attack by macroscopic natural enemies (hymenopteran parasitoids or vertebrate and invertebrate predators). By far, the most important factor affecting survival and causes of mortality within trees was the presence of co—occurring larvae on leaves (i.e., intraspecific competition). Simulated folivory in the first growing season did not affect folivory by Cameraria or other folivorous arthropods in the next season. Colonization, survival, rate of attack by natural enemies, and amount of herbivory by other arthropods in the second growing season were not affected by levels of leaf damage in the first one. Neither survival nor causes of mortality of Cameraria in the second growing season were associated with folivory by endemic leafchewing arthropods. Simulated folivory in the first growing season did, however, reduce leaf production in the second season. These results do not support the hypothesis that insect species complete interspecifically via induced plant responses and their effects on the third trophic level (natural enemies of the herbivores). The effects of simulated (first growing season) and insect (second growing season) folivory via induced plant responses on the Cameraria population was negligible relative to intraspecific interactions. Further, my results do not support the notion that folivore—induced responses are defensive and that plants have evolved these responses to manipulate the third trophic level. In natural settings, other factors that influence population dynamics of phytophagous insects, such as intraspecific competition and interactions with microparasites, may obscure any negative effects of herbivore—induced plant responses on interactions among herbivore species and their macroscopic natural enemies.

A Neighborhood Analysis of Herbivory in Bouteloua Gracilis

This study examined whether an individual plant's risk of herbivory was affected by its nearest neighbor. Individually potted tillers of Bouteloua gracilis were placed in a natural habitat with one of two neighbors (B. gracilis conspecifics or Aristida spp.), and in one of two cover treatments (high: in center of neighbor canopy, and low: at periphery of canopy). After one month, the experimental tillers were collected and scored for herbivory. We found that the less palatable neighbor, Aristida spp., reduced the probability that herbivores would feed upon experimental tillers in one of the two years of our study, but in both years increased the amount of feeding on those tillers that were attacked. The amount of cover did not alter the proportion of plants fed upon, but did affect the number of feeding marks for plants that were fed upon. Our results demonstrate that small—scale spatial pattern within a community is an important determinant of herbivory. A tiller's neighbor exerted a stronger effect on the amount of herbivory it experienced than did either history of previous herbivory or larger scale spatial effects. Our study also reveals that the ways in which neighbors affect herbivory are complex and may vary from year to year.