Biodiversity status of a protected area in West Himalaya: Askot Wildlife Sanctuary

SUMMARY

Biodiversity of a protected area of West Himalaya (Askot Wildlife Sanctuary) was studied and analysed for landscape, faunal and floral diversity. The forest and pasture land, ideal habitats for the flora and fauna, covered nearly 52% and 12%, respectively, of total reported area. Among the fauna Himalayan musk deer (Moschus chrysogaster), thar (Himitragus jemlahicus), snow leopard (Panthera uncia), koklas (Pucrassia macrolophas), monal (Lophophorus impejanus) and snow cock (Tetragalus tibetanus) are threatened species. Plant diversity is represented by 1262 species of vascular plants (Angiosperm 1112, Gymnosperm 7, Pteridophytes 143 taxa). Diversity of the species within families, genera, habitats, communities and along vertical gradient zone was analysed. Maximum diversity existed in the family Orchidaceae (120 taxa), genera Polystichum (13 taxa), altitude zone (1001–2000 m; 860 taxa), habitat (forest; 623 taxa) and community (Banj oak: 92 taxa). Seventy-one families were found to be monotypic. Species were further analysed for ethnobotanical use (medicine: 70, edible: 55, fodder: 115, fuel: 31, house building: 13 etc.), domesticated diversity (crops: 19, vegetables: 26, fruits: 16), agroforestry or marginal, threatened and endemic diversity. Similarity in species composition within the habitats indicated maximum similarity in areas of shrubberies and alpine meadows/ slopes (71.65%) and exposed open/grassy slopes and shady moist places (47.32%). 432 (34.2%) taxa are native to Indian Himalaya of which 24 are endemic and 235 are near endemics. 65.8% of taxa are represented in the neighbouring areas and other regions of the globe. Ten taxa occurring in the Sanctuary have been already recorded in the Red Data Book of Indian Plants. Conservation and management of species is focused.     

Divergent composition but similar function of soil food webs of individual plants: plant species and community effects

Soils are extremely rich in biodiversity, and soil organisms play pivotal roles in supporting terrestrial life, but the role that individual plants and plant communities play in influencing the diversity and functioning of soil food webs remains highly debated. Plants, as primary producers and providers of resources to the soil food web, are of vital importance for the composition, structure, and functioning of soil communities. However, whether natural soil food webs that are completely open to immigration and emigration differ underneath individual plants remains unknown. In a biodiversity restoration experiment we first compared the soil nematode communities of 228 individual plants belonging to eight herbaceous species. We included grass, leguminous, and non-leguminous species. Each individual plant grew intermingled with other species, but all plant species had a different nematode community. Moreover, nematode communities were more similar when plant individuals were growing in the same as compared to different plant communities, and these effects were most apparent for the groups of bacterivorous, carnivorous, and omnivorous nematodes. Subsequently, we analyzed the composition, structure, and functioning of the complete soil food webs of 58 individual plants, belonging to two of the plant species, Lotus corniculatus (Fabaceae) and Plantago lanceolata (Plantaginaceae). We isolated and identified more than 150 taxa/groups of soil organisms. The soil community composition and structure of the entire food webs were influenced both by the species identity of the plant individual and the surrounding plant community. Unexpectedly, plant identity had the strongest effects on decomposing soil organisms, widely believed to be generalist feeders. In contrast, quantitative food web modeling showed that the composition of the plant community influenced nitrogen mineralization under individual plants, but that plant species identity did not affect nitrogen or carbon mineralization or food web stability. Hence, the composition and structure of entire soil food webs vary at the scale of individual plants and are strongly influenced by the species identity of the plant. However, the ecosystem functions these food webs provide are determined by the identity of the entire plant community.     

Wild fruits as a contribution to sustainable rural development: a case study from the Garhwal Himalaya

Garhwal Himalaya is an important source of wild fruit species. These wild fruit trees grow abundantly across an altitudinal gradient of Himalaya and the majority of them bear fruits during summer. Fruit varieties are eaten raw by the local inhabitants of the region and whilst they are a rich source of protein, carbohydrate, fat and other elements, compared to cultivated fruits, they have not yet been considered as a source of alternative food products. About 13 potentially exploitable species of wild fruits and one semi-domesticated species having high potential for exploitation were selected for study; six (Aegle marmelos, Berberis asiatica, Hippophae rhamnoides, Myrica nagi, Rubus ellipticus and Prunus armeniaca) were examined in detail for their economic potential. Among the wild fruits, Hippophae rhamnoides was found to be economically efficient, followed by Aegle marmelos, Rubus ellipticus and Myrica nagi, respectively. Prunus armeniaca, a semi-domesticated and less utilized fruit of the higher Himalaya, provides better economic returns on an annual basis. The authors have recently made an attempt to utilize these wild fruits as a source of income, particularly for poor rural inhabitants and unemployed youths of the region by making a variety of edible products such as jam, jelly, juice, squash, sauce, etc. The enterprise was demonstrated to the people to encourage them to adopt it in the form of a small village-level cottage industry. The present paper discusses the distribution, botany, phenology, yield, ethnobotany, and uses of these species, and the cost-benefit analysis of food products prepared from them.     

Effects of Cattle Grazing on Diversity in Ephemeral Wetlands

Abstract:  Cattle are usually thought of as a threat to biodiversity. In regions threatened by exotic species invasion and lacking native wild grazers, however, cattle may produce the type of disturbance that helps maintain diverse communities. Across 72 vernal pools, I examined the effect of different grazing treatments (ungrazed, continuously grazed, wet-season grazed and dry-season grazed) on vernal-pool plant and aquatic faunal diversity in the Central Valley of California. After 3 years of treatment, ungrazed pools had 88% higher cover of exotic annual grasses and 47% lower relative cover of native species than pools grazed at historical levels (continuously grazed). Species richness of native plants declined by 25% and aquatic invertebrate richness was 28% lower in the ungrazed compared with the continuously grazed treatments. Release from grazing reduced pool inundation period by 50 to 80%, making it difficult for some vernal-pool endemic species to complete their life cycle. My results show that one should not assume livestock and ranching operations are necessarily damaging to native communities. In my central California study site, grazing helped maintain native plant and aquatic diversity in vernal pools.     

Wild plants in everyday use: conservation towards sustainable livelihoods in Nigeria

SUMMARY

Despite the declining volumes of biotic resources flowing from natural ecosystems, no sustainable rural-based programmes have been put in place to stabilize habitats and diversify products to meet the needs and livelihoods of forest-dependent communities. Nevertheless, there is increasing evidence that agricultural expansion and rising demands for forest resources are increasingly depleting the forests. Within these extremes, daily used wild plants that sustain rural communities are under threat of over-exploitation.

This study identified major daily used wild plants in rural environments, examined their use categories, and suggested suitable ways to conserve these plants in order to improve the biodiversity capital and stabilize rural livelihoods. Results of data analysis showed that: (i) about 96 species of wild plants were in daily use for food, energy, medicine, shelter and cultural festivals; (ii) the management and utilization of daily used wild plants were based on traditional knowledge that had become inefficient as a result of resource scarcity and loss of habitats. In these circumstances, resource utilisation is leading to the loss of species; (iii) the resource users were willing to conserve wild plants on private lands to meet their ways of life. The success of wild plant conservation however, hinges on the provision of infrastructures for smallholder farmers who are willing to plant trees on their lands. There is urgent need for those responsible for conserving the forests and the environment (Federal Ministry of Environment) to design and implement suitable programmes that will accommodate the needs of the rural people in conserving wild plants in daily use in the country.     

Native and exotic plant species exhibit similar population dynamics during succession

A growing body of literature has led to the debate in invasion biology whether exotic species perform within communities differently than native taxa due to inherent advantages. To address this issue, the population dynamics of native and exotic plant species were assessed from a 48-year record of permanent plot data from the Hutcheson Memorial Forest Center (New Jersey, USA) to determine rate of increase, lag time, maximum frequency, and the year of peak frequency. Overall, native and exotic species exhibited very similar population dynamics. Rates of increase and length of lag times were similar between native and exotic taxa but were strongly influenced by plant life form. Short-lived species were characterized by rapid population growth rates and short lag times. Growth rates decreased and lag times increased with species longevity. Overall, correlations between population metrics were the same in native and exotic taxa, suggesting similar trade-offs in life history patterns. The one difference observed was that, in native species, peak frequency was negatively associated with the year of peak frequency (i.e., early-successional species tended to become more abundant), while there was no relationship in exotic species. These analyses show that exotic species behave in essentially the same way as native taxa within dynamic communities. This suggests that abundant native and exotic plant species are exploiting the same range of ecological strategies resulting in similar roles within communities.     

Protection versus culture-driven exploitation of wild plant resources: the case on Changbai Mountain

Under Chinese culture it is believed that herbal medicine is always safe and wild food is always healthy. Generally, the rarer a plant, the higher its value. The booming economy in China has promoted tourism development in wilderness areas and wild medicinal and food plants are part of the attraction to tourists. Conflicts between wild plant exploitation and protection have emerged in many parts of China, such as Changbai Mountain. Changbai Mountain supports numerous medicinal and food plants but many have become rare and endangered. This paper numerically evaluates 30 plant species that have relatively high conservation value for each type (medicinal, ornamental and food), and briefly describes the uses of four to five top ranked species per type that need more protection on Changbai Mountain. This paper also addresses some tree species with important timber values on Changbai Mountain. Over 90% of China's medicinal, ornamental and food plant species, as well as valuable timber trees are found in the conifer–broadleaf mixed forest zone across the boundary of Changbai Mountain Nature Reserve. It is a major challenge to protect the native biodiversity of mixed forest on Changbai Mountain and more efforts need to be made to protect rare and endangered plant species with high economic value.     

Human impacts, plant invasion, and imperiled plant species in California.

Invasive species are one of the fastest growing conservation problems. These species homogenize the world's flora and fauna, threaten rare and endemic species, and impose large economic costs. Here, we examine the distribution of 834 of the more than 1000 exotic plant taxa that have become established in California, USA. Total species richness increases with net primary productivity; however, the exotic flora is richest in low-lying coastal sites that harbor large numbers of imperiled species, while native diversity is highest in areas with high mean elevation. Weedy and invasive exotics are more tightly linked to the distribution of imperiled species than the overall pool of exotic species. Structural equation modeling suggests that while human activities, such as urbanization and agriculture, facilitate the initial invasion by exotic plants, exotics spread ahead of the front of human development into areas with high numbers of threatened native plants. The range sizes of exotic taxa are an order of magnitude smaller than for comparable native taxa. The current small range size of exotic species implies that California has a significant "invasion debt" that will be paid as exotic plants expand their range and spread throughout the state.     

Are soil mite assemblages structured by the identity of native and invasive alien grasses?

Associations between plants and animals in aboveground communities are often predictable and specific. This has been exploited for the purposes of estimating the diversity of animal species based on the diversity of plant species. The introduction of invasive alien plants into an ecosystem can result in dramatic changes in both the native plant and animal assemblages. Few data exist at the species level to determine whether belowground animal assemblages share the same degree of association to plants. The hypotheses that soil mites (Acari) form assemblages specifically associated with different native grass species in an unmanipulated natural ecosystem and that invasive alien grasses will impact soil mite assemblage composition in this setting were tested. Soil mites sampled beneath five native and two invasive alien species of grasses at the Konza Prairie Biological Station, Kansas, USA, were similarly abundant, species rich, diverse, and taxonomically distinct. No mite species had affinities for a specific grass species. There was no evidence from analysis of similarity, canonical correspondence analysis, or a nonparametric assemblage analysis that the assemblage composition of soil mites was specific to grass species. Results suggest that soil mite assemblages were more related to characteristics of the plant assemblage as a whole or prevailing soil conditions. The most recent invasive alien grass did not support a successionally younger mite fauna, based on the ratio of mesostigmatid to oribatid mites, and neither of the two invasive grasses influenced mite assemblage structure, possibly because they had not yet substantially altered the soil environment. Our results suggest that extrapolations of soil mite diversity based on assumptions of plant specificity would be invalid.     

Impact of Native Plants on Bird and Butterfly Biodiversity in Suburban Landscapes

Abstract:  Managed landscapes in which non-native ornamental plants are favored over native vegetation now dominate the United States, particularly east of the Mississippi River. We measured how landscaping with native plants affects the avian and lepidopteran communities on 6 pairs of suburban properties in southeastern Pennsylvania. One property in each pair was landscaped entirely with native plants and the other exhibited a more conventional suburban mixture of plants—a native canopy with non-native groundcover and shrubs. Vegetation sampling confirmed that total plant cover and plant diversity did not differ between treatments, but non-native plant cover was greater on the conventional sites and native plant cover was greater on the native sites. Several avian (abundance, species richness, biomass, and breeding-bird abundance) and larval lepidopteran (abundance and species richness) community parameters were measured from June 2006 to August 2006. Native properties supported significantly more caterpillars and caterpillar species and significantly greater bird abundance, diversity, species richness, biomass, and breeding pairs of native species. Of particular importance is that bird species of regional conservation concern were 8 times more abundant and significantly more diverse on native properties. In our study area, native landscaping positively influenced the avian and lepidopteran carrying capacity of suburbia and provided a mechanism for reducing biodiversity losses in human-dominated landscapes.     

森林土壤种子库研究进展

土壤种子库与物种多样性存在密切相关性,森林土壤种子库是植被天然更新的物质基础。文章阐述了森林土壤种子库的内涵、森林生态系统土壤种子库的基本特征及其主要研究方法,探讨了影响种子库的基本因素及当前极为关注的热点问题。在受损森林生态系统目标树种培养、植被群落快速恢复和生态系统科学管理等领域仍存在一些理论和实践急待解决的问题,如随着群落进展演替土壤种子库种子数量在增加而质量却在逐渐下降,面临如何解决生态系统健康稳定发育和物种多样性长期维持问题。文章认为今后应加强土壤种子库与生物多样性保护、防止外来物种入侵乡土物种利用及对全球变化的响应等领域的研究工作,以期为从事森林土壤种子库研究和退化森林植被群落恢复实践提供理论指导。     

The Potential Conservation Value of Non‐Native Species

Abstract: Non‐native species can cause the loss of biological diversity (i.e., genetic, species, and ecosystem diversity) and threaten the well‐being of humans when they become invasive. In some cases, however, they can also provide conservation benefits. We examined the ways in which non‐native species currently contribute to conservation objectives. These include, for example, providing habitat or food resources to rare species, serving as functional substitutes for extinct taxa, and providing desirable ecosystem functions. We speculate that non‐native species might contribute to achieving conservation goals in the future because they may be more likely than native species to persist and provide ecosystem services in areas where climate and land use are changing rapidly and because they may evolve into new and endemic taxa. The management of non‐native species and their potential integration into conservation plans depends on how conservation goals are set in the future. A fraction of non‐native species will continue to cause biological and economic damage, and substantial uncertainty surrounds the potential future effects of all non‐native species. Nevertheless, we predict the proportion of non‐native species that are viewed as benign or even desirable will slowly increase over time as their potential contributions to society and to achieving conservation objectives become well recognized and realized.     

Effect of Vertebrate Grazing on Plant and Insect Community Structure

Abstract: We compared species diversity of plants and insects among grazed and ungrazed areas of Ponderosa pine–grassland communities in Arizona. Plant species richness was higher in two of three grassland communities that were grazed by native elk and deer and domestic cattle than in ungrazed areas inside a series of three large (approximately 40-ha) grazing exclosures. Similarly, plant species richness was higher in grazed areas relative to ungrazed areas at one of two series of smaller (approximately 25-m²) and short-term exclosure sites. Evenness of plant distribution, however, was greater inside ungrazed long-term exclosures but was reduced inside ungrazed short-term exclosures relative to grazed areas. Relative abundances of forbs, grasses, trees, and shrubs, and native and introduced plants did not differ between the long- and short-term grazing exclosures and their grazed counterparts. Relative abundances of some plant species changed when grazers were excluded, however. In contrast, insect species richness was not different between grazed and ungrazed habitats, although insect abundance increased 4- to 10-fold in ungrazed vegetation. Our results suggest that vertebrate grazing may increase plant richness, even in nutrient-poor, semi-arid grasslands, but may decrease insect abundances.     

Ranking Lepidopteran Use of Native Versus Introduced Plants

Abstract:  In light of the wide-scale replacement of native plants in North America with introduced, invasive species and noninvasive ornamental plants that evolved elsewhere, we compared the value of native and introduced plants in terms of their ability to serve as host plants for Lepidoptera. Insect herbivores such as Lepidoptera larvae are critically important components of terrestrial food webs and any reduction in their biomass or diversity due to the loss of acceptable host plants is predicted to reduce the production of the many insectivores in higher trophic levels. We conducted an exhaustive search of host records in the literature. We used the data we gathered to rank all 1385 plant genera that occur in the mid-Atlantic states of the United States by their ability to support Lepidoptera richness. Statistical comparisons were made with Welch's test for equality of means. Woody plants supported more species of moths and butterflies than herbaceous plants, native plants supported more species than introduced plants, and native woody plants with ornamental value supported more Lepidoptera species than introduced woody ornamentals. All these differences were highly significant. Our rankings provide a relative measure that will be useful for restoration ecologists, landscape architects and designers, land managers, and landowners who wish to raise the carrying capacity of particular areas by selecting plants with the greatest capacity for supporting biodiversity.     

Aquatic plant community invasibility and scale-dependent patterns in native and invasive species richness

Invasive species richness often is negatively correlated with native species richness at the small spatial scale of sampling plots, but positively correlated in larger areas. The pattern at small scales has been interpreted as evidence that native plants can competitively exclude invasive species. Large-scale patterns have been understood to result from environmental heterogeneity, among other causes. We investigated species richness patterns among submerged and floating-leaved aquatic plants (87 native species and eight invasives) in 103 temperate lakes in Connecticut (northeastern USA) and found neither a consistently negative relationship at small (3-m2) scales, nor a positive relationship at large scales. Native species richness at sampling locations was uncorrelated with invasive species richness in 37 of the 60 lakes where invasive plants occurred; richness was negatively correlated in 16 lakes and positively correlated in seven. No correlation between native and invasive species richness was found at larger spatial scales (whole lakes and counties). Increases in richness with area were uncorrelated with abiotic heterogeneity. Logistic regression showed that the probability of occurrence of five invasive species increased in sampling locations (3 m2, n = 2980 samples) where native plants occurred, indicating that native plant species richness provided no resistance against invasion. However, the probability of three invasive species' occurrence declined as native plant density increased, indicating that density, if not species richness, provided some resistance with these species. Density had no effect on occurrence of three other invasive species. Based on these results, native species may resist invasion at small spatial scales only in communities where density is high (i.e., in communities where competition among individuals contributes to community structure). Most hydrophyte communities, however, appear to be maintained in a nonequilibrial condition by stress and/or disturbance. Therefore, most aquatic plant communities in temperate lakes are likely to be vulnerable to invasion.     

Paleoecology and the Coarse-Filter Approach to Maintaining Biological Diversity

Abstract: The difficulties of saving millions of species from extinction often cause conservationists to focus on a higher level of biological organization, the community. They do so for two reasons: (1) communities are considered important biological entities in their own right; and (2) conserving representative samples of communities is seen as an efficient way to maintain high levels of species diversity. This approach will work if the chosen communities contain almost all species. Because it potentially saves most but not all species, community conservation is a "coarse-filter" approach to the maintenance of biological diversity, and contrasts with the "fine-filter" approach of saving individual species. Paleoecological information on the distribution of plant taxa in North America, however, indicates that most modern plant communities are less than 8,000 years old and therefore are not highly organized units reflecting long-term co-evolution among species. Rather, they are only transitory assemblages or co-occurrences among plant taxa that have changed in abundance, distribution, and association in response to the large climate changes of the past 20,000 years. During periods when climate changes are large, communities are too ephemeral to be considered important biological entities in their own right. Large climatic changes are also likely to occur during the next century because of increased concentrations of CO₂, and we therefore propose that the coarse-filter approach to selecting nature reserves should be more strongly influenced by the distribution of physical environments than by the distribution of modern communities. Ideally, nature reserves should also encompass a broad enough range of environments to allow organisms to adjust their local distribution in response to long-term environmental change and should be connected by regional corridors that would allow species to change their geographic distributions.     

Diversity-invasibility across an experimental disturbance gradient in Appalachian Forests

Research examining the relationship between community diversity and invasions by nonnative species has raised new questions about the theory and management of biological invasions. Ecological theory predicts, and small-scale experiments confirm, lower levels of nonnative species invasion into species-rich compared to species-poor communities, but observational studies across a wider range of scales often report positive relationships between native and nonnative species richness. This paradox has been attributed to the scale dependency of diversity-invasibility relationships and to differences between experimental and observational studies. Disturbance is widely recognized as an important factor determining invasibility of communities, but few studies have investigated the relative and interactive roles of diversity and disturbance on nonnative species invasion. Here, we report how the relationship between native and nonnative plant species richness responded to an experimentally applied disturbance gradient (from no disturbance up to clearcut) in oak-dominated forests. We consider whether results are consistent with various explanations of diversity-invasibility relationships including biotic resistance, resource availability, and the potential effects of scale (1 m2 to 2 ha). We found no correlation between native and nonnative species richness before disturbance except at the largest spatial scale, but a positive relationship after disturbance across scales and levels of disturbance. Post-disturbance richness of both native and nonnative species was positively correlated with disturbance intensity and with variability of residual basal area of trees. These results suggest that more nonnative plants may invade species-rich communities compared to species-poor communities following disturbance.     

How Many Plants Feed the World?

Abstract: FAO food supply data for 146 countries were analyzed to identify the plant commodities that account for the top 90% of each country's per capita supply of food plants by weighs calories, protein, and fat. The plant commodities were divided into two groups: species commodities, such as "cabbages," that can be attributed to particular species; and general commodities, such as "hydrogenated oils," whose species composition is not known. A total of 82 species commodities and 28 general commodities contribute 90% of national per capita supplies of food plants. The 82 species commodities consist of 103 species. Fifty-six of these commodities, comprising 75 species, individually account for 5% or more of at least one county's supply of a nutritional category (plant weight, plant calories, plant protein, plant fag. These figures are several times higher than previous findings that very few (7–30) plant species feed the world. The new figures are considered more accurate because they derive from national supply rather than global production data and from several separate measures of the importance of a food commodity rather than one. The results suggest that (1) plant species diversity remains a significant factor for world food supply; and (2) a conservation priority is to maintain both this wider away of species and the diversity of genetic variants that comprise each species.     

Abiotic constraints eclipse biotic resistance in determining invasibility along experimental vernal pool gradients.

Effective management of invasive species requires that we understand the mechanisms determining community invasibility. Successful invaders must tolerate abiotic conditions and overcome resistance from native species in invaded habitats. Biotic resistance to invasions may reflect the diversity, abundance, or identity of species in a community. Few studies, however, have examined the relative importance of abiotic and biotic factors determining community invasibility. In a greenhouse experiment, we simulated the abiotic and biotic gradients typically found in vernal pools to better understand their impacts on invasibility. Specifically, we invaded plant communities differing in richness, identity, and abundance of native plants (the "plant neighborhood") and depth of inundation to measure their effects on growth, reproduction, and survival of five exotic plant species. Inundation reduced growth, reproduction, and survival of the five exotic species more than did plant neighborhood. Inundation reduced survival of three species and growth and reproduction of all five species. Neighboring plants reduced growth and reproduction of three species but generally did not affect survival. Brassica rapa, Centaurea solstitialis, and Vicia villosa all suffered high mortality due to inundation but were generally unaffected by neighboring plants. In contrast, Hordeum marinum and Lolium multiflorum, whose survival was unaffected by inundation, were more impacted by neighboring plants. However, the four measures describing plant neighborhood differed in their effects. Neighbor abundance impacted growth and reproduction more than did neighbor richness or identity, with growth and reproduction generally decreasing with increasing density and mass of neighbors. Collectively, these results suggest that abiotic constraints play the dominant role in determining invasibility along vernal pool and similar gradients. By reducing survival, abiotic constraints allow only species with the appropriate morphological and physiological traits to invade. In contrast, biotic resistance reduces invasibility only in more benign environments and is best predicted by the abundance, rather than diversity, of neighbors. These results suggest that stressful environments are not likely to be invaded by most exotic species. However, species, such as H. marinum, that are able to invade these habitats require careful management, especially since these environments often harbor rare species and communities.     

A simple plant mutation abets a predator-diversity cascade

Resource consumption often increases with greater consumer biodiversity. This could result either from complementarity among consumers or the inclusion of particular key species, and it is often difficult to differentiate between these two mechanisms. We exploited a simple plant mutation (reduced production of surface waxes) to alter foraging within a community of aphid predators, and thus perhaps shift the nature of resulting predator diversity effects. We found that greater predator species richness dramatically increased prey suppression and plant biomass only on mutant, reduced-wax pea plants (Pisum sativum). On pea plants from a sister line with wild type, waxier plant surfaces, predator species richness did not influence predators' impacts on herbivores or plants. Thus, a change in plant surface structure acted to turn on, or off, the cascading effects of predator diversity. Greater predator richness encouraged higher densities of true predators but did not lead to greater reproduction by a parasitoid, Aphidius ervi; fecundity of each natural enemy species was similar for the two plant types. Behavioral observations indicated that although A. ervi was less likely to forage within species-rich predator communities, low-wax plants mitigated this interference by encouraging generally greater A. ervi foraging and thus high rates of aphid dislodgement (aphids dropped from plants to escape A. ervi, but not the other predators). Thus, only species-rich, low-wax plants simultaneously encouraged strong species-specific effects of A. ervi, and strong complementarity among the other predator species. In summary, our study provides evidence that diversity effects in predator assemblages are sensitive to habitat characteristics. Further, we show that a simple plant morphological trait, controlled by a single gene mutation, can dramatically alter the cascading effects of predator species richness on herbivores and plants.