Large mammalian herbivores and woody plant species diversity in Zimbabwe

Study sites from various tree savannas and miombo woodland with adjacentareas with different herbivore species (game and cattle) and stocking rates wereselected from around Zimbabwe. Using the fence-lines separating the adjacentareas, 60 m² plots were placed on both sides of thefence at 18 randomly chosen positions. The identity and number of plants of eachwoody species were recorded in paired 60 m² plots. Therewere no significant differences in the woody species richness between pairedplots for any of the fence-line contrasts. For only two of the fence-linecontrasts were there significant differences (P < 0.05)in the relative abundance of woody species. For the first fence-line contrast,the stocking rates were the same, but the herbivore species present weredifferent, while for the second fence-line contrast, the numbers of herbivorespecies present were the same, but the stocking rates differed. Even thoughthere were no differences in the numbers of woody plant species present, therewere differences in the woody plant species and the numbers of plants of eachspecies: the second most common species was different for three fence-linecontrasts and the third most common species was different for four fence-linecontrasts.     

Effects of plant diversity on invertebrate herbivory in experimental grassland

The rate at which a plant species is attacked by invertebrate herbivores has been hypothesized to depend on plant species richness, yet empirical evidence is scarce. Current theory predicts higher herbivore damage in monocultures than in species-rich mixtures. We quantified herbivore damage by insects and molluscs to plants in experimental plots established in 2002 from a species pool of 60 species of Central European Arrhenatherum grasslands. Plots differed in plant species richness (1, 2, 4, 8, 16, 60 species), number of functional groups (1, 2, 3, 4), functional group and species composition. We estimated herbivore damage by insects and molluscs at the level of transplanted plant individuals (“phytometer” species Plantago lanceolata, Trifolium pratense, Rumex acetosa) and of the entire plant community during 2003 and 2004. In contrast to previous studies, our design allows specific predictions about the relative contributions of functional diversity, plant functional identity, and species richness in relation to herbivory. Additionally, the phytometer approach is new to biodiversity-herbivory studies, allowing estimates of species-specific herbivory rates within the larger biodiversity-ecosystem functioning context. Herbivory in phytometers and experimental communities tended to increase with plant species richness and the number of plant functional groups, but the effects were rarely significant. Herbivory in phytometers was in some cases positively correlated with community biomass or leaf area index. The most important factor influencing invertebrate herbivory was the presence of particular plant functional groups. Legume (grass) presence strongly increased (decreased) herbivory at the community level. The opposite pattern was found for herbivory in T. pratense phytometers. We conclude that (1) plant species richness is much less important than previously thought and (2) plant functional identity is a much better predictor of invertebrate herbivory in temperate grassland ecosystems.     

Experimental Manipulation of Grassland Plant Diversity Induces Complex Shifts in Aboveground Arthropod Diversity

Changes in producer diversity cause multiple changes in consumer communities through various mechanisms. However, past analyses investigating the relationship between plant diversity and arthropod consumers focused only on few aspects of arthropod diversity, e.g. species richness and abundance. Yet, shifts in understudied facets of arthropod diversity like relative abundances or species dominance may have strong effects on arthropod-mediated ecosystem functions. Here we analyze the relationship between plant species richness and arthropod diversity using four complementary diversity indices, namely: abundance, species richness, evenness (equitability of the abundance distribution) and dominance (relative abundance of the dominant species). Along an experimental gradient of plant species richness (1, 2, 4, 8, 16 and 60 plant species), we sampled herbivorous and carnivorous arthropods using pitfall traps and suction sampling during a whole vegetation period. We tested whether plant species richness affects consumer diversity directly (i), or indirectly through increased productivity (ii). Further, we tested the impact of plant community composition on arthropod diversity by testing for the effects of plant functional groups (iii). Abundance and species richness of both herbivores and carnivores increased with increasing plant species richness, but the underlying mechanisms differed between the two trophic groups. While higher species richness in herbivores was caused by an increase in resource diversity, carnivore richness was driven by plant productivity. Evenness of herbivore communities did not change along the gradient in plant species richness, whereas evenness of carnivores declined. The abundance of dominant herbivore species showed no response to changes in plant species richness, but the dominant carnivores were more abundant in species-rich plant communities. The functional composition of plant communities had small impacts on herbivore communities, whereas carnivore communities were affected by forbs of small stature, grasses and legumes. Contrasting patterns in the abundance of dominant species imply different levels of resource specialization for dominant herbivores (narrow food spectrum) and carnivores (broad food spectrum). That in turn could heavily affect ecosystem functions mediated by herbivorous and carnivorous arthropods, such as herbivory or biological pest control.     

Spatial patterns of woody plant and bird diversity: functional relationships or environmental effects?

Aim To understand cross‐taxon spatial congruence patterns of bird and woody plant species richness. In particular, to test the relative roles of functional relationships between birds and woody plants, and the direct and indirect environmental effects on broad‐scale species richness of both groups. Location Kenya. Methods Based on comprehensive range maps of all birds and woody plants (native species > 2.5 m in height) in Kenya, we mapped species richness of both groups. We distinguished species richness of four different avian frugivore guilds (obligate, partial, opportunistic and non‐frugivores) and fleshy‐fruited and non‐fleshy‐fruited woody plants. We used structural equation modelling and spatial regressions to test for effects of functional relationships (resource–consumer interactions and vegetation structural complexity) and environment (climate and habitat heterogeneity) on the richness patterns. Results Path analyses suggested that bird and woody plant species richness are linked via functional relationships, probably driven by vegetation structural complexity rather than trophic interactions. Bird species richness was determined in our models by both environmental variables and the functional relationships with woody plants. Direct environmental effects on woody plant richness differed from those on bird richness, and different avian consumer guilds showed distinct responses to climatic factors when woody plant species richness was included in path models. Main conclusions Our results imply that bird and woody plant diversity are linked at this scale via vegetation structural complexity, and that environmental factors differ in their direct effects on plants and avian trophic guilds. We conclude that climatic factors influence broad‐scale tropical bird species richness in large part indirectly, via effects on plants, rather than only directly as often assumed. This could have important implications for future predictions of animal species richness in response to climate change.     

Stability of ecosystem properties in response to above-ground functional group richness and composition

While there has been a rapidly increasing research effort focused on understanding whether and how composition and richness of species and functional groups may determine ecosystem properties, much remains unknown about how these community attributes affect the dynamic properties of ecosystems. We conducted an experiment in 540 mini‐ecosystems in glasshouse conditions, using an experimental design previously shown to be appropriate for testing for functional group richness and composition effects in ecosystems. Artificial communities representing 12 different above‐ground community structures were assembled. These included treatments consisting of monoculture and two‐ and four‐species mixtures from a pool of four plant species; each plant species represented a different functional group. Additional treatments included two herbivore species, either singly or in mixture, and with or without top predators. These experimental units were then either subjected to an experimentally imposed disturbance (drought) for 40 d or left undisturbed. Community composition and drought both had important effects on plant productivity and biomass, and on several below‐ground chemical and biological properties, including those linked to the functioning of the decomposer subsystem. Many of these compositional effects were due to effects both of plant and of herbivore species. Plant functional group richness also exerted positive effects on plant biomass and productivity, but not on any of the below‐ground properties. Above‐ground composition also had important effects on the response of below‐ground properties to drought and thus influenced ecosystem stability (resistance); effects of composition on drought resistance of above‐ground plant response variables and soil chemical properties were weaker and less consistent. Despite the positive effects of plant functional group richness on some ecosystem properties, there was no effect of richness on the resistance of any of the ecosystem properties we considered. Although herbivores had detectable effects on the resistance of some ecosystem properties, there were no effects of the mixed herbivore species treatment on resistance relative to the single species herbivore treatments. Increasing above‐ground food chain length from zero to three trophic levels did not have any consistent effect on the stability of ecosystem properties. There was no evidence of either above‐ground composition or functional group richness affecting the recovery rate of ecosystem properties from drought and hence ecosystem resilience. Our data collectively point to the role of composition (identity of functional group), but not functional group richness, in determining the stability (resistance to disturbance) of ecosystem properties, and indicates that the nature of the above‐ground community can be an important determinant of the consistency of delivery of ecosystem services.     

Responses of arthropods to plant diversity: changes after pollution cessation

Data collected from three different polluted sites in the vicinity of a phosphate fertilizer factory that was closed in 1990 are used to test with Mantel tests and smoothing techniques whether the rapid increase of plant species richness following cessation of pollution enhanced associated arthropod assemblage diversity. 132 plant species (between 1990 and 1999) and 66 413 individuals of 680 arthropod species (using sweep net sampling between 1990 and 1996) were recorded. Using top soil pH as a representative pollution parameter we detected an increase of plant species richness, effective diversity and evenness of plant community with decreasing pH both in space and time. While the richness of all studied functional groups of herbivores increased with plant species richness, only the richness of one carnivore functional group showed a similar pattern. Plant species richness was significantly correlated to the abundance patterns of two herbivore and two carnivore groups. But contrary to theoretical predictions consumer abundance tended to decrease with increasing plant diversity only between a plant species richness range of 10 to ca 35. Our results support the findings of previous studies that highlight how increased plant species and functional group richness may result in higher herbivore species richness, and that carnivore richness may be influenced by herbivore and detritivore richness. The functional group approach used in this study has enabled us to detected the very individual interaction patterns that occur between different groups within the same trophic level.     

Herbivore species richness, composition and community structure mediate predator richness effects and top-down control of herbivore biomass

Changes in predator species richness can have important consequences for ecosystem functioning at multiple trophic levels, but these effects are variable and depend on the ecological context in addition to the properties of predators themselves. Here, we report an experimental study to test how species identity, community attributes, and community structure at the herbivore level moderate the effects of predator richness on ecosystem functioning. Using mesocosms containing predatory insects and aphid prey, we independently manipulated species richness at both predator and herbivore trophic levels. Community structure was also manipulated by changing the distribution of herbivore species across two plant species. Predator species richness and herbivore species richness were found to negatively interact to influence predator biomass accumulation, an effect which is hypothesised to be due to the breakdown of functional complementarity among predators in species-rich herbivore assemblages. The strength of predator suppression of herbivore biomass decreased as herbivore species richness and distribution across host plants increased, and positive predator richness effects on herbivore biomass suppression were only observed in herbivore assemblages of relatively low productivity. In summary, the study shows that the species richness, productivity and host plant distribution of prey communities can all moderate the general influence of predators and the emergence of predator species richness effects on ecosystem functioning.     

Plant species loss decreases arthropod diversity and shifts trophic structure

Plant diversity is predicted to be positively linked to the diversity of herbivores and predators in a foodweb. Yet, the relationship between plant and animal diversity is explained by a variety of competing hypotheses, with mixed empirical results for each hypothesis. We sampled arthropods for over a decade in an experiment that manipulated the number of grassland plant species. We found that herbivore and predator species richness were strongly, positively related to plant species richness, and that these relationships were caused by different mechanisms at herbivore and predator trophic levels. Even more dramatic was the threefold increase, from low- to high-plant species richness, in abundances of predatory and parasitoid arthropods relative to their herbivorous prey. Our results demonstrate that, over the long term, the loss of plant species propagates through food webs, greatly decreasing arthropod species richness, shifting a predator-dominated trophic structure to being herbivore dominated, and likely impacting ecosystem functioning and services.     

Effects of restriction of wild herbivore movement on woody and herbaceous vegetation in the Okavango Delta Botswana

We conducted herbaceous and woody vegetation surveys across Botswana's southern Okavango Buffalo Fence, which separates wildlife management from tribal grazing areas, to determine whether the restriction of herbivore movement by fencing has influenced vegetation composition, diversity and structure. We sampled herbaceous and woody vegetation at twenty paired sites every 2 km along the fence. For the herbaceous layer, ten 0.25 m² quadrats were laid every 10 m perpendicular to the fence; while for the woody vegetation, variable quadrat plots were used. Paired t‐tests were run. Results show little difference in forb or grass composition between the two sides. However, the cover and diversity of many woody species were greatly reduced across most height classes on the wildlife management side. Overall woody cover on the wildlife side of the fence was nearly half that of the tribal grazing side (t = 2.83, P = 0.011, df = 19), while overall wood diversity was also significantly less on the wildlife side (t = 3.29, P = 0.004, df = 19). We conclude that the concentration of wildlife due to the fence, while improving habitat for some herbivore species, is having a detrimental effect on plant diversity in general.     

Insects affect relationships between plant species richness and ecosystem processes

This study examined whether insects can alter relationships between plant species diversity and ecosystem function in grassland communities, by (i) altering biomass across a plant diversity gradient, (ii) altering relative abundances of plant species, or (iii) altering ecosystem function directly. We measured herbivore damage on seminatural grassland plots planted with 1, 2, 4, 8, or 12 plant species, and compared plant biomass in a subset of these plots with replicates in which insect levels were reduced. Plant biomass and herbivore damage increased with species richness. Reducing insect populations resulted in greater evenness of relative plant species abundances and revealed a strong positive relationship between plant species richness and above-ground biomass. Reducing insects also changed the relationship between plant species richness and decomposition. Plant species mixtures and their relative abundances partially explained plant biomass results, but not decomposition results. These results suggest that insects can alter relationships between plant diversity and ecosystem processes through all three mechanisms.     

Short-term responses of the understory to the removal of plant functional groups in the cold-temperate deciduous forest

It is widely believed that functional diversity contributes to the stability of ecosystems. Indeed, greater redundancy among species within functional groups and greater complementarity among functional groups within communities should increase the resistance and resilience of ecosystems. In the present study, we tested for functional group complementarity by examining how the loss of specific functional groups may alter the role that other groups play in ecosystem functions. We removed different functional groups, one at a time, from the understory of three maple-dominated forests in southern Québec (Canada) and followed the understory response over a 2-year period. The experimental design included a control and five removal treatments. Five functional groups were defined: spring-flowering ephemeral species; spring-flowering persistent species; summer-flowering species; fern species; and seedlings and juveniles of woody species. Richness, cover, soil pH and organic matter content were determined after two years of removal. The results of our experiment revealed that richness was significantly lower than what we expected when spring-flowering persistent species or seedlings and juveniles of woody species were removed, suggesting not only direct but also indirect positive effects of both of these groups on understory richness (mostly through effects on summer-flowering species and fern species). Removal of the seedlings and juveniles of woody species and, to a lesser extent, of spring-flowering persistent species and of fern species lead to a decrease in the cover of summer-flowering species, implying a positive effect of the former groups on the latter. The cover–richness relationship in the control and in each one of the five removal treatments was positive and well fitted by a linear regression. Yet, the slope of the relationship differed among treatments, but not between the control and any one of the removal treatments (pair-wise comparisons). Our results suggest that the different functional groups are complementary and that positive interactions predominate over negative ones. Contrary to common belief, understory plants can respond quite rapidly to changes in community functional composition. Although we have not investigated the specific mechanisms responsible for the short-term responses reported here, we suggest that complex intergroup interactions may favour functional diversity and enhance ecosystem functions.     

Land-use intensification reduces functional redundancy and response diversity in plant communities

Ecosystem resilience depends on functional redundancy (the number of species contributing similarly to an ecosystem function) and response diversity (how functionally similar species respond differently to disturbance). Here, we explore how land-use change impacts these attributes in plant communities, using data from 18 land-use intensity gradients that represent five biomes and > 2800 species. We identify functional groups using multivariate analysis of plant traits which influence ecosystem processes. Functional redundancy is calculated as the species richness within each group, and response diversity as the multivariate within-group dispersion in response trait space, using traits that influence responses to disturbances. Meta-analysis across all datasets showed that land-use intensification significantly reduced both functional redundancy and response diversity, although specific relationships varied considerably among the different land-use gradients. These results indicate that intensified management of ecosystems for resource extraction can increase their vulnerability to future disturbances.
Ecology Letters (2010) 13: 76–86     

放牧强度和地形对内蒙古典型草原物种多度分布的影响

为了更好地理解放牧对草原生态系统物种多度分布格局的影响, 以及常见种和稀有种对维持群落多样性的作用, 以内蒙古典型草原为研究对象, 基于长期放牧控制实验平台(包括7个载畜率水平(0、1.5、3.0、4.5、6.0、7.5、9.0 sheep·hm^-2)和两种地形系统(平地和坡地)), 研究了群落内全部物种、常见种和稀有种的丰富度和多度对放牧强度的响应规律, 并选取对数正态模型、对数级数模型和幂分割模型, 对物种多度数据进行拟合。结果表明: 1)平地系统中, 物种丰富度和多度在低放牧强度下(1.5、3.0 sheep·hm^-2)增加, 而在中、高度放牧强度下(4.5-9.0 sheep·hm^-2)降低, 全部物种的多度分布在大多数放牧强度下符合幂分割模型, 在高放牧强度下也符合对数正态模型; 坡地系统中, 物种丰富度和多度随着放牧强度增加而显著降低, 全部物种的多度分布在各个放牧强度下, 均符合幂分割模型和对数正态模型。2)随着放牧强度增加, 常见种的多度响应趋势与全部物种的响应趋势一致, 其多度分布均符合幂分割模型和对数正态模型; 稀有种的丰富度响应趋势与全部物种的响应趋势一致, 其多度分布符合幂分割模型, 同时也部分符合对数正态和对数级数模型。总之, 适宜的载畜率有利于生物多样性和初级生产力的提高, 平地系统中物种多度的响应在一定程度上支持放牧优化假说; 而坡地系统中不同物种多度的响应差异说明: 确定最佳载畜率时, 还需要考虑地形因素的影响。此外, 模型的拟合结果表明: 生态位分化机制对内蒙古典型草原物种多度分布起着主要作用, 常见种和稀有种通过不同的响应方式共同维持着草原生态系统的物种多样性。     

Contrasting effects of plant richness and composition on insect communities: a field experiment

We experimentally separated the effects of two components of plant diversity-plant species richness and plant functional group richness-on insect communities. Plant species richness and plant functional group richness had contrasting effects on insect abundances, a result we attributed to three factors. First, lower insect abundances at higher plant functional group richness were explained by a sampling effect, which was caused by the increasing likelihood that one low-quality group, C4 grasses, would be present and reduce average insect abundances by 25%. Second, plant biomass, which was positively related to plant functional group richness, had a strong, positive effect on insect abundances. Third, a positive effect of plant species richness on insect abundances may have been caused by greater availability of alternate plant resources or greater vegetational structure. In addition, a greater diversity of insect species, whose individual abundances were often unaffected by changes in plant species richness, may have generated higher total community abundances. After controlling for the strong, positive influence of insect abundance on insect diversity through rarefaction, insect species richness increased as plant species richness and plant functional group richness increased. Although these variables did not explain a high proportion of variation individually, plant species richness and plant functional group richness had similar effects on insect diversity and opposing effects on insect abundances, and both factors may explain how the loss of plant diversity influences higher trophic levels.     

不同间伐强度对南亚热带杉木人工林林下植物功能群的影响

间伐作为我国森林经营的主要措施之一,对提高森林生态系统内部生物多样性起着不可忽视的作用。然而,不同间伐强度对森林林下植物功能群的影响程度尚不明确。以广西凭祥热林中心经过4种不同强度抚育间伐8年后的杉木人工林为研究对象(轻度间伐ST,34%;中度间伐MT,50%;重度间伐HT,74%;不进行间伐的对照,CK),对林下植被及其环境因子进行调查和测定。研究结果表明:不同间伐强度对禾草植物功能群的物种丰富度均无显著影响(P0.05),MT显著增加杂草植物功能群的物种丰富度(P0.05),HT显著提高蕨类植物功能群的物种丰富度(P0.05),ST显著增加木本植物功能群的物种丰富度(P0.05),与CK相比,ST、MT和HT均能显著增加藤本植物功能群的物种丰富度(P0.05);不同间伐强度对禾草和木本植物功能群的重要值均无显著影响(P0.05),但HT显著降低了杂草植物功能群的重要值(P0.05),ST显著降低了蕨类植物功能群的重要值(P0.05),ST显著增加藤本植物功能群的重要值(P0.05)。主成分分析(PCA)表明,ST和HT的林下植物功能群组成和分布与对照组相比均发生了显著的变异。方差分解分析(Variation partitioning analyses)结果显示,林分和土壤因子对林下植物功能群变异的解释率相似,二者在决定杉木人工林林下植物功能群变异中都起着重要作用。     

The effects of long-term nitrogen loading on grassland insect communities

Just as long-term nitrogen loading of grasslands decreases plant species richness and increases plant biomass, we have found that nitrogen loading decreases insect species richness and increases insect abundances. We sampled 54 plots that had been maintained at various rates of nitrogen addition for 14 years. Total insect species richness and effective insect diversity, as well as herbivore and predator species richness, were significantly, negatively related to the rate of nitrogen addition. However, there was variation in trophic responses to nitrogen. Detritivore species richness increased as nitrogen addition increased, and parasitoids showed no response. Insect abundances, measured as the number of insects and insect biovolume (an estimate of biomass), were significantly, positively related to the rate of nitrogen addition, as were the abundances of herbivores and detritivores. Parasitoid abundance was negatively related to the rate of nitrogen addition. Changes in the insect community were correlated with changes in the plant community. As rates of nitrogen addition increased, plant species richness decreased, plant productivity and plant tissue nitrogen increased, and plant composition shifted from C₄ to C₃ grass species. Along this gradient, total insect species richness and effective insect diversity were most strongly, positively correlated with plant species richness. Insect biovolume was negatively correlated with plant species richness. Responses of individual herbivores varied along the nitrogen gradient, but numbers of 13 of the 18 most abundant herbivores were positively correlated with their host plant biomass. Although insect communities did not respond as strongly as plant communities, insect species richness, abundance, and composition were impacted by nitrogen addition. This study demonstrates that long-term nitrogen loading affects the entire food chain, simplifying both plant and insect communities. Received: 18 May 1999 / Accepted: 5 January 2000     

Grazing without grasses: Effects of introduced livestock on plant community composition in an arid environment in northern Patagonia

Question: How does grazing intensity affect plant density, cover and species richness in an Patagonian arid ecosystem? Location: Monte steppe ecoregion, SW Argentina. Methods: I analysed the effect of grazing on plant density, cover and species richness using a stocking rate gradient within the same habitat. Six paddocks were used with stocking rates ranging between 0.002 – 0.038 livestock/ha. Plant density, species richness, plant cover and percentage of grazed branches were determined by sampling plots within each paddock. The percentage of grazed branches was used as an independent measurement of grazing intensity. Results: Higher stocking rates were related to lower plant density, species richness and plant cover. The paddock with the lowest grazing intensity had 86% more plants per unit area, 63% more plant cover and 48% higher species richness. The percentage of grazed branches and the quantity of dung increased with stocking rate. Conclusions: Introduced livestock seriously affect native vegetation in the Patagonian Monte. The damage observed in this xerophytic plant community suggests that plant adaptations to aridity do not provide an advantage to tolerate or avoid grazing by vertebrate herbivores in this region. Plant degradation in this arid environment is comparable to the degradation found in more humid ecosystems.     

Experimental tests of the dependence of arthropod diversity on plant diversity

ABSTRACT Because a diversity of resources should support a diversity of consumers, most models predict that increasing plant diversity increases animal diversity. We report results of a direct experimental test of the dependence of animal diversity on plant diversity. We sampled arthropods in a well-replicated grassland experiment in which plant species richness and plant functional richness were directly manipulated. In simple regressions, both the number of species planted ([Formula: see text] transformed) and the number of functional groups planted significantly increased arthropod species richness but not arthropod abundance. However, the number of species planted was the only significant predictor of arthropod species richness when both predictor variables were included in ANOVAs or a MANOVA. Although highly significant, arthropod species richness regressions had low [Formula: see text] values, high intercepts (24 arthropod species in monocultures), and shallow slopes. Analyses of relations among plants and arthropod trophic groups indicated that herbivore diversity was influenced by plant, parasite, and predator diversity. Furthermore, herbivore diversity was more strongly correlated with parasite and predator diversity than with plant diversity. Together with regression results, this suggests that, although increasing plant diversity significantly increased arthropod diversity, local herbivore diversity is also maintained by, and in turn maintains, a diversity of parasites and predators.     

Functional identity versus species richness: herbivory resistance in plant communities

The resistance of a plant community against herbivore attack may depend on plant species richness, with monocultures often much more severely affected than mixtures of plant species. Here, we used a plant–herbivore system to study the effects of selective herbivory on consumption resistance and recovery after herbivory in 81 experimental grassland plots. Communities were established from seed in 2002 and contained 1, 2, 4, 8, 16 or 60 plant species of 1, 2, 3 or 4 functional groups. In 2004, pairs of enclosure cages (1 m tall, 0.5 m diameter) were set up on all 81 plots. One randomly selected cage of each pair was stocked with 10 male and 10 female nymphs of the meadow grasshopper, Chorthippus parallelus. The grasshoppers fed for 2 months, and the vegetation was monitored over 1 year. Consumption resistance and recovery of vegetation were calculated as proportional changes in vegetation biomass. Overall, grasshopper herbivory averaged 6.8%. Herbivory resistance and recovery were influenced by plant functional group identity, but independent of plant species richness and number of functional groups. However, herbivory induced shifts in vegetation composition that depended on plant species richness. Grasshopper herbivory led to increases in herb cover at the expense of grasses. Herb cover increased more strongly in species-rich mixtures. We conclude that selective herbivory changes the functional composition of plant communities and that compositional changes due to selective herbivory depend on plant species richness.