The alpine cushion plant Silene acaulis as foundation species: a bug's-eye view to facilitation and microclimate

Alpine ecosystems are important globally with high levels of endemic and rare species. Given that they will be highly impacted by climate change, understanding biotic factors that maintain diversity is critical. Silene acaulis is a common alpine nurse plant shown to positively influence the diversity and abundance of organisms--predominantly other plant species. The hypothesis that cushion or nurse plants in general are important to multiple trophic levels has been proposed but rarely tested. Alpine arthropod diversity is also largely understudied worldwide, and the plant-arthropod interactions reported are mostly negative, that is,. herbivory. Plant and arthropod diversity and abundance were sampled on S. acaulis and at paired adjacent microsites with other non-cushion forming vegetation present on Whistler Mountain, B.C., Canada to examine the relative trophic effects of cushion plants. Plant species richness and abundance but not Simpson's diversity index was higher on cushion microsites relative to other vegetation. Arthropod richness, abundance, and diversity were all higher on cushion microsites relative to other vegetated sites. On a microclimatic scale, S. acaulis ameliorated stressful conditions for plants and invertebrates living inside it, but the highest levels of arthropod diversity were observed on cushions with tall plant growth. Hence, alpine cushion plants can be foundation species not only for other plant species but other trophic levels, and these impacts are expressed through both direct and indirect effects associated with altered environmental conditions and localized productivity. Whilst this case study tests a limited subset of the membership of alpine animal communities, it clearly demonstrates that cushion-forming plant species are an important consideration in understanding resilience to global changes for many organisms in addition to other plants.     

Exploring the relationship between macrofungi diversity, abundance, and vascular plant diversity in semi-natural and managed forests in north-east Hungary

The diversity of easy-to-study organisms (e.g. vascular plants) is often used as a proxy for the diversity of other organisms whose investigation needs more effort, time and specialist knowledge. Some previous studies have found positive relationships between plant and macrofungal diversity and thus support this approach, while others question this practice. Our aim was to explore the possibility of using plant diversity as surrogate for macrofungal diversity in the forests of the Pannonian ecoregion. A total of 19 permanent plots in north-east Hungary were sampled for vascular plants and macrofungi. The effect on macrofungal abundance and diversity, as well as degradation level, of plant evenness and richness was tested using generalized linear models. Species richness of macrofungi assemblages proved to be independent of the diversity and naturalness of vascular plant communities; however, there was congruence in the composition of the two communities. In contrast to diversity, macrofungi abundance was significantly negatively correlated to plant species richness. There was a hump-backed relationship between the abundance of terricolous macrofungi and the degradation level estimated on the basis of the occurrence of vascular plants, although degradation did not influence the abundance of lignicolous macrofungi. Our results question the reliability of decisions on nature conservation actions based on a few groups of easy-to-observe organisms, and underline the necessity of studying as wide a range of taxonomic groups as possible.     

Indirect interactions mediated by leaf shelters in animal–plant communities

Leaf shelters indirectly mediate interactions in animal–plant communities by providing the occupants with several kinds of benefits, as physical ecosystem engineering. The occupants benefit from favorable microhabitat, reduction in antiherbivore defense, and protection from natural enemies. The primary shelter maker has to spend energy and time and producing silk, but shelter users have great advantages without incurring costs. Shelter users consist of a wide range of arthropod taxa and can be divided into two groups: coexisting organisms that live with a primary shelter maker in the same shelter, and secondary users, which inhabit a leaf shelter after it is utilized by a shelter maker. Leaf shelters mediate interactions between (1) primary shelter makers and coexisting organisms or (2) primary shelter makers and secondary users, (3) secondary users, (4) shelter users and their natural enemies, and (5) primary shelter makers, secondary users, and their host plants. Most interactions between primary shelter makers and coexisting organisms constitute a direct trophic linkage rather than indirect ones. There are actually unidirectional beneficial effects from a primary shelter maker to secondary shelter users, whereas leaf shelters mediate competition and predation among shelter users. By providing a leaf shelter, a shelter maker leads to increased diversity of interactions. Leaf shelters modify the distribution of organisms on the host plant and influence herbivory on the host plant. In tritrophic interactions, leaf shelters act as cues for natural enemies that search for a shelter user as prey. Furthermore, by enhancing habitat heterogeneity, leaf shelters affect the abundance and species richness of arthropods on host plants. Received: July 24, 2000 / Accepted: February 15, 2001     

Disentangling vegetation diversity from climate–energy and habitat heterogeneity for explaining animal geographic patterns

Broad‐scale animal diversity patterns have been traditionally explained by hypotheses focused on climate–energy and habitat heterogeneity, without considering the direct influence of vegetation structure and composition. However, integrating these factors when considering plant–animal correlates still poses a major challenge because plant communities are controlled by abiotic factors that may, at the same time, influence animal distributions. By testing whether the number and variation of plant community types in Europe explain country‐level diversity in six animal groups, we propose a conceptual framework in which vegetation diversity represents a bridge between abiotic factors and animal diversity. We show that vegetation diversity explains variation in animal richness not accounted for by altitudinal range or potential evapotranspiration, being the best predictor for butterflies, beetles, and amphibians. Moreover, the dissimilarity of plant community types explains the highest proportion of variation in animal assemblages across the studied regions, an effect that outperforms the effect of climate and their shared contribution with pure spatial variation. Our results at the country level suggest that vegetation diversity, as estimated from broad‐scale classifications of plant communities, may contribute to our understanding of animal richness and may be disentangled, at least to a degree, from climate–energy and abiotic habitat heterogeneity.     

Plant composition,not richness,drives occurrence of specialist herbivores

1. How herbivore plant diversity relationships are shaped by the interplay of biotic and abiotic environmental variables is only partly understood. For instance, plant diversity is commonly assumed to determine abundance and richness of associated specialist herbivores. However, this relationship can be altered when environmental variables such as temperature covary with plant diversity. 2. Using gall‐inducing arthropods as focal organisms, biotic and abiotic environmental variables were tested for their relevance to specialist herbivores and their relationship to host plants. In particular, the hypothesis that abundance and richness of gall‐inducing arthropods increase with plant richness was addressed. Additionally, the study asked whether communities of gall‐inducing arthropods match the communities of their host plants. 3. Neither abundance nor species richness of gall‐inducing arthropods was correlated with plant richness or any other of the tested environmental variables. Instead, the number of gall species found per plant decreased with plant richness. This indicates that processes of associational resistance may explain the specialised plant herbivore relationship in our study. 4. Community composition of gall‐inducing arthropods matched host plant communities. In specialised plant herbivore relationships, the presence of obligate host plant species is a prerequisite for the occurrence of its herbivores. 5. It is concluded that the abiotic environment may only play an indirect role in shaping specialist herbivore communities. Instead, the occurrence of specialist herbivore communities might be best explained by plant species composition. Thus, plant species identity should be considered when aiming to understand the processes that shape diversity patterns of specialist herbivores.     

Flavonoids as developmental regulators

Flavonoids, usually regarded as dispensable phytochemicals derived from plant secondary metabolism, play important roles in the biology of plants by affecting several developmental processes. Bioactive flavonoids also signal to microbes, serve as allelochemicals and are important nutraceuticals in the animal diet. Despite the significant progress made in identifying flavonoid pathway genes and regulators, little is currently known about the protein targets of flavonoids in plant or animal cells. Recently, there have been advances in our understanding of the roles that flavonoids play in developmental processes of plants. The multiple cellular roles of flavonoids can reflect their chemical diversity, or might suggest the existence of cellular targets shared between many of these seemingly disparate processes.     

An ecological perspective on bacterial biodiversity

Bacteria may be one of the most abundant and species-rich groups of organisms, and they mediate many critical ecosystem processes. Despite the ecological importance of bacteria, past practical and theoretical constraints have limited our ability to document patterns of bacterial diversity and to understand the processes that determine these patterns. However, recent advances in molecular techniques that allow more thorough detection of bacteria in nature have made it possible to examine such patterns and processes. Here, we review recent studies of the distribution of free-living bacterial diversity and compare our current understanding with what is known about patterns in plant and animal diversity. From these recent studies a preliminary picture is emerging: bacterial diversity may exhibit regular patterns, and in some cases these patterns may be qualitatively similar to those observed for plants and animals.     

Woody plant phylogenetic diversity mediates bottom–up control of arthropod biomass in species-rich forests

Global change is predicted to cause non-random species loss in plant communities, with consequences for ecosystem functioning. However, beyond the simple effects of plant species richness, little is known about how plant diversity and its loss influence higher trophic levels, which are crucial to the functioning of many species-rich ecosystems. We analyzed to what extent woody plant phylogenetic diversity and species richness contribute to explaining the biomass and abundance of herbivorous and predatory arthropods in a species-rich forest in subtropical China. The biomass and abundance of leaf-chewing herbivores, and the biomass dispersion of herbivores within plots, increased with woody plant phylogenetic diversity. Woody plant species richness had much weaker effects on arthropods, but interacted with plant phylogenetic diversity to negatively affect the ratio of predator to herbivore biomass. Overall, our results point to a strong bottom–up control of functionally important herbivores mediated particularly by plant phylogenetic diversity, but do not support the general expectation that top–down predator effects increase with plant diversity. The observed effects appear to be driven primarily by increasing resource diversity rather than diversity-dependent primary productivity, as the latter did not affect arthropods. The strong effects of plant phylogenetic diversity and the overall weaker effects of plant species richness show that the diversity-dependence of ecosystem processes and interactions across trophic levels can depend fundamentally on non-random species associations. This has important implications for the regulation of ecosystem functions via trophic interaction pathways and for the way species loss may impact these pathways in species-rich forests.     

Impacts of invasive plants on resident animals across ecosystems,taxa, and feeding types: a global assessment

As drivers of global change, biological invasions have fundamental ecological consequences. However, it remains unclear how invasive plant effects on resident animals vary across ecosystems, animal classes, and functional groups. We performed a comprehensive meta‐analysis covering 198 field and laboratory studies reporting a total of 3624 observations of invasive plant effects on animals. Invasive plants had reducing (56%) or neutral (44%) effects on animal abundance, diversity, fitness, and ecosystem function across different ecosystems, animal classes, and feeding types while we could not find any increasing effect. Most importantly, we found that invasive plants reduced overall animal abundance, diversity and fitness. However, this significant overall effect was contingent on ecosystems, taxa, and feeding types of animals. Decreasing effects of invasive plants were most evident in riparian ecosystems, possibly because frequent disturbance facilitates more intense plant invasions compared to other ecosystem types. In accordance with their immediate reliance on plants for food, invasive plant effects were strongest on herbivores. Regarding taxonomic groups, birds and insects were most strongly affected. In insects, this may be explained by their high frequency of herbivory, while birds demonstrate that invasive plant effects can also cascade up to secondary consumers. Since data on impacts of invasive plants are rather limited for many animal groups in most ecosystems, we argue for overcoming gaps in knowledge and for a more differentiated discussion on effects of invasive plant on native fauna.     

环境DNA技术在地下生态学中的应用

地下生态过程是生态系统结构、功能和过程研究中最不确定的因素。由于技术和方法的限制,作为"黑箱"的地下生态系统已经成为限制生态学发展的瓶颈,也是未来生态学发展的主要方向。环境DNA技术,是指从土壤等环境样品中直接提取DNA片段,然后通过DNA测序技术来定性或定量化目标生物,以确定目标生物在生态系统中的分布及功能特征。环境DNA技术已成功用于地下生态过程的研究。目前,环境DNA技术在土壤微生物多样性及其功能方面的研究相对成熟,克服了土壤微生物研究中不能培养的问题,可以有效地分析土壤微生物的群落组成、多样性及空间分布,尤其是宏基因组学技术的发展,使得微生物生态功能方面的研究成为可能;而且,环境DNA技术已经在土壤动物生态学的研究中得到了初步应用,可快速分析土壤动物的多样性及其分布特征,更有效地鉴定出未知的或稀少的物种,鉴定土壤动物类群的幅度较宽;部分研究者通过提取分析土壤中DNA片段信息对生态系统植物多样性及植物分类进行了研究,其结果比传统的植物分类及物种多样性测定更精确,改变了以往对植物群落物种多样性模式的理解。同时,环境DNA技术克服传统根系研究方法中需要洗根、分根、只能测定单物种根系的局限,降低根系研究中细根区分的误差,并探索性地用于细根生物量的研究。主要综述了基于环境DNA技术的分子生物学方法在土壤微生物多样性及功能、土壤动物多样性、地下植物多样性及根系生态等地下生态过程研究中的应用进展。环境DNA技术对于以土壤微生物、土壤动物及地下植物根系为主体的地下生态学过程的研究具有革命性意义,并展现出良好的应用前景。可以预期,分子生物学技术与传统的生态学研究相结合将成为未来地下生态学研究的一个发展趋势。     

Nonnative plant invasion increases urban vegetation structure and influences arthropod communities

Aim

Ecological theory and empirical evidence indicate that greater structural complexity and diversity in plant communities increases arthropod abundance and diversity. Nonnative plants are typically associated with low arthropod abundance and diversity due to lack of evolutionary history. However, nonnative plants increase the structural complexity of forests, as is common in urban forests. Therefore, urban forests are ideal ecosystems to determine whether structural complexity associated with nonnative plants will increase abundance and diversity of arthropods, as predicted by complexity literature, or whether structural complexity associated with nonnative plants will be depauperate of arthropods, as predicted by nonnative plant literature.

Location

We sampled 24 urban temperate deciduous and mixed forests in two cites, Raleigh, North Carolina and Newark, Delaware, in the eastern United States.

Methods

We quantified ground cover vegetation and shrub layer vegetation in each forest and created structural complexity metrics to represent total, nonnative and native understory vegetation structural complexity. We vacuum sampled arthropods from vegetation and quantified the abundance, biomass, richness and diversity of spiders and non-spider arthropods.

Results

Nonnative plants increase understory vegetation complexity in urban forests. In Raleigh and Newark, we found support for the hypotheses that dense vegetation will increase arthropod abundance and biomass, and against the hypothesis that nonnative vegetation will decrease arthropods. Urban forest arthropod abundance and biomass, but not diversity, increased with greater nonnative and native structural complexity.

Main Conclusions

Invaded urban forests may provide adequate food in the form of arthropod biomass to transfer energy to the next trophic level, but likely fail to provide ecological services and functions offered by diverse species, like forest specialists. Urban land managers should survey urban forests for nonnative and native plant communities and prioritize replacing dense nonnative plants with native species when allocating vegetation maintenance resources.     

Soil Environmental Conditions and Microbial Build-Up Mediate the Effect of Plant Diversity on Soil Nitrifying and Denitrifying Enzyme Activities in Temperate Grasslands

Random reductions in plant diversity can affect ecosystem functioning, but it is still unclear which components of plant diversity (species number – namely richness, presence of particular plant functional groups, or particular combinations of these) and associated biotic and abiotic drivers explain the observed relationships, particularly for soil processes. We assembled grassland communities including 1 to 16 plant species with a factorial separation of the effects of richness and functional group composition to analyze how plant diversity components influence soil nitrifying and denitrifying enzyme activities (NEA and DEA, respectively), the abundance of nitrifiers (bacterial and archaeal amoA gene number) and denitrifiers (nirK, nirS and nosZ gene number), and key soil environmental conditions. Plant diversity effects were largely due to differences in functional group composition between communities of identical richness (number of sown species), though richness also had an effect per se. NEA was positively related to the percentage of legumes in terms of sown species number, the additional effect of richness at any given legume percentage being negative. DEA was higher in plots with legumes, decreased with increasing percentage of grasses, and increased with richness. No correlation was observed between DEA and denitrifier abundance. NEA increased with the abundance of ammonia oxidizing bacteria. The effect of richness on NEA was entirely due to the build-up of nitrifying organisms, while legume effect was partly linked to modified ammonium availability and nitrifier abundance. Richness effect on DEA was entirely due to changes in soil moisture, while the effects of legumes and grasses were partly due to modified nitrate availability, which influenced the specific activity of denitrifiers. These results suggest that plant diversity-induced changes in microbial specific activity are important for facultative activities such as denitrification, whereas changes in microbial abundance play a major role for non-facultative activities such as nitrification.     

Intraspecific chemical diversity among neighbouring plants correlates positively with plant size and herbivore load but negatively with herbivore damage

Intraspecific plant diversity can modify the properties of associated arthropod communities and plant fitness. However, it is not well understood which plant traits determine these ecological effects. We explored the effect of intraspecific chemical diversity among neighbouring plants on the associated invertebrate community and plant traits. In a common garden experiment, intraspecific diversity among neighbouring plants was manipulated using three plant populations of wild cabbage that differ in foliar glucosinolates. Plants were larger, harboured more herbivores, but were less damaged when plant diversity was increased. Glucosinolate concentration differentially correlated with generalist and specialist herbivore abundance. Glucosinolate composition correlated with plant damage, while in polycultures, variation in glucosinolate concentrations among neighbouring plants correlated positively with herbivore diversity and negatively with plant damage levels. The results suggest that intraspecific variation in secondary chemistry among neighbouring plants is important in determining the structure of the associated insect community and positively affects plant performance.     

Diversity of plant–animal interactions: Possibilities for a new plant defense indicator value?

The interactions between herbivores and plants are of general interest in ecology. Even though the extensive research carried out during the last decades has culminated in many theories, additional studies are necessary to validate these findings. In particular, the hypotheses dealing with the complex interrelations of plant defense mechanisms and herbivores continue to be debated.In this paper, we develop a new indicator value that quantifies the defense mechanisms of Central European woody plants against large mammalian herbivores. The indicator value is based on three plant-specific traits: chemical defense (toxic compounds, digestion inhibitors), mechanical defense and leaf size. Our validation of the newly established indicator shows that evergreen woody plants have a significantly higher indicator value than deciduous woody plants. Moreover, plant defense is correlated with growth height: woody plants growing in the browsing zone preferred by large mammalian herbivores have significantly higher levels of defense compared with woody plants capable of growth high above the reach of large herbivores.We conclude that the new plant defense indicator value is a valuable tool for the validation of existing hypotheses and habitat calibration on a statistical basis. The quantification of plant mechanisms of defense against large herbivores produces a significantly better understanding of the multifaceted nature of plant–animal interactions and should contribute positively to future studies.     

The Microbial <Emphasis Type="BoldItalic">Phyllo</Emphasis>geography of the Carnivorous Plant <Emphasis Type="BoldItalic">Sarracenia alata</Emphasis>

Carnivorous pitcher plants host diverse microbial communities. This plant–microbe association provides a unique opportunity to investigate the evolutionary processes that influence the spatial diversity of microbial communities. Using next-generation sequencing of environmental samples, we surveyed microbial communities from 29 pitcher plants (Sarracenia alata) and compare community composition with plant genetic diversity in order to explore the influence of historical processes on the population structure of each lineage. Analyses reveal that there is a core S. alata microbiome, and that it is similar in composition to animal gut microfaunas. The spatial structure of community composition in S. alata (phyllogeography) is congruent at the deepest level with the dominant features of the landscape, including the Mississippi river and the discrete habitat boundaries that the plants occupy. Intriguingly, the microbial community structure reflects the phylogeographic structure of the host plant, suggesting that the phylogenetic structure of bacterial communities and population genetic structure of their host plant are influenced by similar historical processes.     

Abundance,origin, and phylogeny of plants do not predict community‐level patterns of pathogen diversity and infection

Pathogens have the potential to shape plant community structure, and thus, it is important to understand the factors that determine pathogen diversity and infection in communities. The abundance, origin, and evolutionary relationships of plant hosts are all known to influence pathogen patterns and are typically studied separately. We present an observational study that examined the influence of all three factors and their interactions on the diversity of and infection of several broad taxonomic groups of foliar, floral, and stem pathogens across three sites in a temperate grassland in the central United States. Despite that pathogens are known to respond positively to increases in their host abundances in other systems, we found no relationship between host abundance and either pathogen diversity or infection. Native and exotic plants did not differ in their infection levels, but exotic plants hosted a more generalist pathogen community compared to native plants. There was no phylogenetic signal across plants in pathogen diversity or infection. The lack of evidence for a role of abundance, origin, and evolutionary relationships in shaping patterns of pathogens in our study might be explained by the high generalization and global distributions of our focal pathogen community, as well as the high diversity of our plant host community. In general, the community‐level patterns of aboveground pathogen infections have received less attention than belowground pathogens, and our results suggest that their patterns might not be explained by the same drivers.     

Context‐dependent biotic interactions control plant abundance across altitudinal environmental gradients

Many biotic interactions influence community structure, yet most distribution models for plants have focused on plant competition or used only abiotic variables to predict plant abundance. Furthermore, biotic interactions are commonly context‐dependent across abiotic gradients. For example, plant–plant interactions can grade from competition to facilitation over temperature gradients. We used a hierarchical Bayesian framework to predict the abundances of 12 plant species across a mountain landscape and test hypotheses on the context‐dependency of biotic interactions over abiotic gradients. We combined field‐based estimates of six biotic interactions (foliar herbivory and pathogen damage, fungal root colonization, fossorial mammal disturbance, plant cover and plant diversity) with abiotic data on climate and soil depth, nutrients and moisture. All biotic interactions were significantly context‐dependent along temperature gradients. Results supported the stress gradient hypothesis: as abiotic stress increased, the strength or direction of the relationship between biotic variables and plant abundance generally switched from negative (suggesting suppressed plant abundance) to positive (suggesting facilitation/mutualism). For half of the species, plant cover was the best predictor of abundance, suggesting that the prior focus on plant–plant interactions is well‐justified. Explicitly incorporating the context‐dependency of biotic interactions generated novel hypotheses about drivers of plant abundance across abiotic gradients and may improve the accuracy of niche models.     

Construction of Sand Shinnery Oak Communities of the Llano Estacado: Animal Disturbances, Plant Community Structure, and Restoration

In land restoration it is imperative to study the potential role of disturbances, biotic or abiotic, that may provide sites for colonization by specific plants. Disturbances can alter community composition by removing species or allowing others to become established. In communities where animal-generated disturbances open sites for seedling establishment, animals may have important indirect effects on several aspects of plant community structure. Animal disturbances in Quercus havardii communities of western Texas appear to open sites for colonization by herbaceous species. These animal disturbances vary in spatial distribution, density, and abiotic and biotic characteristics. The abundance of herbaceous plant seedlings is positively related to bare ground and the number of distinct disturbances. Thus, the density and the spatial distribution of these disturbances may be expected to have an important influence on the abundance and dispersion of plant species. Therefore, successful restoration efforts of sand shinnery oak communities and other similar habitats must consider the effects of animal disturbances and the role of plant-animal and plant-soil microbe interactions on plant community composition and the maintenance of plant species diversity.     

有机肥和植被去除管理对人工林土壤节肢动物多样性的影响

施用有机肥和林下抚育（植被去除）是人工林重要的管理措施;土壤节肢动物物种丰富,是土壤生态系统的重要组成成分,对环境变化敏感,可以作为森林管理的指示生物。人工林植被去除和施肥管理影响土壤性质、资源输入量及微生物多样性,从而影响土壤节肢动物多样性,但是相关研究还十分缺乏。以沿海地区杨树人工林为对象,研究了施用有机肥和林下植被去除对土壤节肢动物的数量和多样性的影响。结果表明,有机肥和植被去除管理对不同土壤层土壤节肢动物的数量和多样性指标影响不一致。有机肥增加0-10 cm深度土壤节肢动物总数量、蜱螨目数量,降低土壤节肢动物群落物种丰富度、均匀度和Shannon多样性指数;植被去除减少0-10 cm深度土壤节肢动物总数量和弹尾目数量,降低均匀度指数。两种处理对10-20 cm深度土壤节肢动物群落的数量和各多样性指标影响不显著。总体来说（0-20 cm）,有机肥处理土壤节肢动物的数量显著增加,优势类群前气门亚目（Prostigmata）的数量增长为对照的4倍,但是土壤节肢动物群落的均匀度和Shannon多样性指数显著降低,这可能是土壤节肢动物优势类群前气门亚目密度急剧增加,而物种丰富度没有变化所导致;此外,施用有机肥增加了土壤有机质、总氮、有效磷的含量,降低土壤pH值,并且与前气门亚目密度显著相关。林下植被去除没有影响0-20 cm深度土壤节肢动物的数量和各多样性指标。