Does phylogenetic relatedness influence the strength of competition among vascular plants?

A widely assumed but largely untested hypothesis central to ecology and evolutionary biology has been Charles Darwin's suggestion that closely related species will be more ecologically similar, and thus will compete more strongly with each other than they will with more distantly related species. We provide one of the first direct tests of the “competition-relatedness hypothesis” by combining two data sets: the relative competitive ability of 50 vascular plant species competing against 92 competitor species measured in five multi-species experiments, and measures of the phylogenetic relatedness of these species. In contrast to Darwin's assertion, there were weak relationships between the strength of competition and phylogenetic relatedness. Across all species studied, the competition-relatedness relationship was weak and not significant. This overall lack of pattern masked different responses of monocot and eudicot focal (phytometer) species. When monocots served as the focal (phytometer) species, the intensity of competition increased with the phylogenetic distance separating species, while competition decreased with phylogenetic distance for eudicot phytometers. These results were driven by the monocot-eudicot evolutionary split, such that monocots were poor competitors against eudicots, while eudicots are most strongly suppressed by other eudicots. There was no relationship between relatedness and competition for eudicots competing with other eudicots, while monocots did compete more intensely with closely related monocots than with distantly related monocots. Overall, the relationships between competition intensity and relatedness were weak compared to the strong and consistent relationships between competitive ability and functional traits such as plant size that have been reported by other studies. We suggest that Darwin's assertion that competition will be strongest among closely related species is not supported by empirical data, at least for the 142 vascular plant species in this study.     

Metabolic dissimilarity determines the establishment of cross-feeding interactions in bacteria

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Diet quality determines interspecific parasite interactions in host populations

The widespread occurrence of multiple infections and the often vast range of nutritional resources for their hosts allow that interspecific parasite interactions in natural host populations might be determined by host diet quality. Nevertheless, the role of diet quality with respect to multispecies parasite interactions on host population level is not clear. We here tested the effect of host population diet quality on the parasite community in an experimental study using Daphnia populations. We studied the effect of diet quality on Daphnia population demography and the interactions in multispecies parasite infections of this freshwater crustacean host. The results of our experiment show that the fitness of a low‐virulent microsporidian parasite decreased in low, but not in high‐host‐diet quality conditions. Interestingly, infections with the microsporidium protected Daphnia populations against a more virulent bacterial parasite. The observed interspecific parasite interactions are discussed with respect to the role of diet quality‐dependent changes in host fecundity. This study reflects that exploitation competition in multispecies parasite infections is environmentally dependent, more in particular it shows that diet quality affects interspecific parasite competition within a single host and that this can be mediated by host population‐level effects.     

两个放牧率下藏羊粪在高寒草甸的分解特征

青藏高原拥有全球独特的放牧系统,国内外较少通过定量控制的放牧试验研究放牧率对畜粪分解的作用。用双层盆叠放法比较高寒草甸两个放牧率下藏羊粪的分解规律。8羊/hm~2放牧率下的分解速率大于16羊/hm~2。随着放牧率增加,羊粪C、N、P的归还量、草地残留和淋溶量及其所占比例上升,C、N的大气排放量增加。粪中P的分解与C/N比负相关,C的分解速率与N/P比正相关。用Olson的指数模型拟合,羊粪分解50%和95%所需时间,除了木质素,粪干物质、C、N、P、纤维素、半纤维素的分解时间16羊/hm~2放牧率下均长于8羊/hm~2放牧率。单位重量粪的分解速率,16羊/hm~2放牧率下较快;单位面积草地上,畜粪的分解在16羊/hm~2放牧率下较快。研究结果对于全球变暖背景下,调整高寒草甸放牧策略有指导作用。     

Response to interspecific vocalizations is affected by degree of phylogenetic relatedness in Streptopelia doves

Owing to common descent, related species often show similarity in a number of traits, including those involved in communication. As a result signal similarity and phylogenetic distance are usually inversly related. However, similarity in signal structure need not correspond with similarity in response to such signals. We tested the hypothesis that individuals are more responsive to signals from closely related species than from distantly related ones. We conducted playback experiments on two turtle dove species (African collared-dove, Streptopelia roseogrisea, and vinaceous dove, Streptopelia vinacea) using conspecific and heterospecific vocalizations. Vocalizations were played from species that differed in degree of relatedness and in relative geographical distribution. This enabled us to separate the effects of phylogeny and those of sympatry. There was an effect of phylogenetic distance, with a decrease in response to playback stimuli as phylogenetic distance increased. The results also suggest a minor effect of sympatry, with the response to sympatric species being lower. Copyright 2001 The Association for the Study of Animal Behaviour.     

Phylogenetic niche conservatism, phylogenetic signal and the relationship between phylogenetic relatedness and ecological similarity among species

Ecologists are increasingly adopting an evolutionary perspective, and in recent years, the idea that closely related species are ecologically similar has become widespread. In this regard, phylogenetic signal must be distinguished from phylogenetic niche conservatism. Phylogenetic niche conservatism results when closely related species are more ecologically similar that would be expected based on their phylogenetic relationships; its occurrence suggests that some process is constraining divergence among closely related species. In contrast, phylogenetic signal refers to the situation in which ecological similarity between species is related to phylogenetic relatedness; this is the expected outcome of Brownian motion divergence and thus is necessary, but not sufficient, evidence for the existence of phylogenetic niche conservatism. Although many workers consider phylogenetic niche conservatism to be common, a review of case studies indicates that ecological and phylogenetic similarities often are not related. Consequently, ecologists should not assume that phylogenetic niche conservatism exists, but rather should empirically examine the extent to which it occurs.     

青藏高原高寒草甸土壤环境对线虫功能多样性的影响

土壤线虫是地下食物网的重要组成部分, 在生态系统能量流动和物质循环中起着至关重要的作用。大量研究报道了肥力等土壤环境对土壤线虫物种多样性及各功能群多度的影响, 而我们对土壤线虫功能多样性如何响应土壤环境变化依然知之甚少。本研究以群落水平个体大小和个体大小多样性表征土壤线虫功能多样性。在青藏高原高寒草甸选择3个研究点, 调查和分析了不同生境(沟底平地、阴坡、阳坡和山顶)土壤线虫物种多样性、各功能群多度和功能多样性及其与土壤理化因子和植物多样性的关系。结果表明: (1)土壤线虫个体多度和物种多样性在阳坡最高, 随土壤pH值和土壤总磷增加而升高; 而基于个体大小的土壤线虫功能多样性主要受土壤养分影响, 随土壤总氮和有机质增加而增加, 随土壤总磷含量增加而减少; (2)食细菌和食真菌线虫多度在沟底最高, 植食与捕食杂食线虫多度在山顶最低; 除捕食杂食线虫外, 各功能群多度也主要随土壤磷增加而升高; 除食真菌线虫外, 各功能群多度随植物物种丰富度的增加而减少。本研究强调了土壤线虫物种和功能多样性受不同土壤环境因子的影响, 丰富了土壤线虫多样性研究的内容, 为理解高寒草甸土壤动物多样性形成、维持和变化提供了更广阔的 视角。     

Growing season ecosystem respirations and associated component fluxes in two alpine meadows on the Tibetan Plateau

From 30 June to 24 September in 2003 ecosystem respiration （Re） in two alpine meadows on the Tibetan Plateau were measured using static chamber- and gas chromatography- （GC） based techniques. Simultaneously, plant removal treatments were set to partition Re into plant autotrophic respiration （Ra） and microbial heterotrophic respiration （Rh）. Results indicated that Re had clear diurnal and seasonal variation patterns in both of the meadows. The seasonal variability of Re at both meadow sites was caused mainly by changes in Ra, rather than Rh. Moreover, atthe Kobresia humilis meadow site （K_site）, Ra and Rh accounted for 54% and 46% of Re, respectively. While at the Potentilla fruticosa scrub meadow （P_site）, the counterparts accounted for 61% and 39%, respectively. T test showed that there was significant difference in Re rates between the two meadows （t = 2.387, P = 0.022）. However, no significant difference was found in Rh rates, whereas a significant difference was observed in Ra rates between the two meadows. Thus, the difference in Re rate between the two meadows was mainly attributed to plant autotrophic respirations. During the growing season, the two meadows showed relatively low Q10 values, suggesting that Re, especially Rh was not sensitive to temperature variation in the growing season. Additionally, Re and Rh at the K_site, as well as Rh at the Psite was negatively correlated with soil moisture, indicating that soil moisture would also play an important role in respirations.     

Life history of the plateau pika (Ochotona curzoniae) in alpine meadows of the Tibetan Plateau

The life history of a species is a result of natural selection and reflects how the species is adapted to its environment. Knowledge of life history is crucial for further ecological studies and conservation management. This paper presents aspects of the life history of the plateau pika (Ochotona curzoniae), a small mammal native to alpine meadows of the Tibetan Plateau. The mean lifespan of juveniles from first litters was longer than the mean lifespan of juveniles from second litters. The population consisted of more juveniles than adults (over-wintered animals) in August and these juveniles came primarily from the first litter of the year. The sex ratio of juveniles was female-biased even though the sex ratio of adults did not differ from 1:1. The mortality rate of juveniles and adults during the warm season (May–August) was greater than the mortality rate of these groups during the cold season (September–April). Mean juvenile growth rate during the warm season was 1.4 g/d and the growth rate of the first litters was remarkably slower than that of the second litters.     

Dynamics of development of juvenile plants on the meadows of the alpine belt of northwest Caucasus

We investigated juvenile plants on the Hedysaro caucasicae-Gerametum gymnocauli meadows (Rabotnova and Onipchenko, 2002) of the alpine meadows of the northwest Caucasus. During the course of 5 years, we considered all juvenile plants on 16 plots of 0.5 m². We recorded 4485 sprouts and monitored their destiny. The dominant species were Hedysarum caucasicum Bieb. and Geranium gymnocaulon DC., and most species of Asteraceae had juvenile plants, but without seeds in soil bank of seeds. The grass species rarely produced sprouts and had seeds in the soil bank. The majority of sprouts died after the first winter. Sprouts of the dominant species were in their juvenile stage for a long time, and the sprouts of other species quickly shifted to the vegetative stage.     

Community assembly along a successional gradient in sub‐alpine meadows of the Qinghai‐Tibetan Plateau,China

Community assembly is a dynamic progression that reflects the interaction of several processes functioning at multiple scales. Understanding how these processes work in communities at different successional stages is important for identifying when regional or local processes are more important for community assembly, and for developing effective preservation and restoration strategies. We examined community assembly using a chronosequence of sub‐alpine meadows in Qinghai‐Tibetan Plateau that range from ‘natural’ (never farmed), to those that have been protected from agricultural exploitation for 1 to 10 years. We tested for shifts in species and traits among meadows and also for changes in environmental and spatial correlates of species distributions within meadows. We found that species richness increased and species composition returned to natural conditions within ten years of protection. These changes coincided with shifts in species traits; abundant species had high seed mass and specific leaf area in late‐successional meadows, whereas the opposite occurred in early‐successional meadows. Despite these shifts among meadows of different ages, spatial distributions of species within meadows did not change – when associated with abiotic variables, these spatial patterns reflected changes in soil pH and nitrogen. There was also no consistent change in the relative importance of environmental and spatial correlates of species distributions within meadows. These trends indicate that local processes of community assembly are similar within meadows even when species in those meadows differ. We conclude that successional change is a large‐scale process that alters the species pool and resulting suite of traits that are present within meadows. As a result, regional planning that incorporates successional age should be the focus for the conservation of diversity in this area. In contrast, local processes work within the constraints of the species pool set by successional age, producing consistent patterns within meadows of different ages.     

Exploring the community phylogenetic structure along the slope aspect of subalpine meadows in the eastern Qinghai–Tibetan Plateau,China

Exploring the community assembly has been important for explaining the maintenance mechanisms of biodiversity and species coexistence, in that it is a central issue in community ecology. Here, we examined patterns of the community phylogenetic structure of the subalpine meadow plant community along the slope gradient in the Qinghai–Tibetan Plateau of China. We surveyed all species and constructed the phylogenetic tree of the plant community based on data from the Angiosperm Phylogeny Group III. We selected the net relative index (NRI) and evaluated the community phylogenetic structure along the five slope plants communities. We found that the phylogenetic structure varied from phylogenetic clustering to phylogenetic overdispersion with the slope aspect from north to south. In the north slope, the community phylogenetically cluster indicated that the limiting similarity played a leading role in the community assembly and the maintenance of biodiversity. Community phylogenetic overdispersion in the east, southeast, and south slopes indicated that habitat filtration was the driving force for community assembly. The NRI index of the northeast slope was close to zero, implying random dispersion. But it may be driven by the neutral process or limiting similarity, in that the community assembly process was the result of a combination of several ecological factors and thus required further study.     

高寒草甸种间性状差异和物种均匀度对物种多样性与功能多样性关系的影响

物种多样性(SD)与功能多样性(FD)之间存在多种关系,但由于生态系统功能主要由物种的功能属性决定,因而功能多样性对生态系统功能的影响大于物种多样性的影响。但在种间性状差异和物种均匀度这两个构成功能多样性的基本成分中,何者对功能多样性影响更大,并进而决定SD-FD关系尚不明确。通过在高寒矮嵩草(Kobresia humilis)草甸为期6a的刈割(留茬1 cm、3 cm及不刈割)和施肥(尿素7.5 g m~(-2)a~(-1)+磷酸二胺1.8 g m~(-2)a~(-1)、不施肥)控制实验,研究了种间性状差异(33个物种13个性状)和物种均匀度(所有物种)对物种多样性(所有物种)与功能多样性(33个物种13个性状)之间关系的影响。研究结果显示:(1)物种多样性与功能多样性正相关,它们与多性状种间差异负相关,而与物种均匀度正相关。物种均匀度是导致功能多样性变化的主要因素,也是导致SD-FD正相关的原因,这是因为随着物种多样性增加,物种均匀度的增加程度大于多性状种间差异的减少程度,因而功能多样性增加,SD-FD正相关;(2)功能多样性指数(FD_(Rao)和FDis)随物种多样性指数(H')减速递增,表明群落存在一定的功能冗余,且功能冗余随物种多样性的增大而增大,但尚未达到产生SD-FD无相关性的极限H'值;(3)功能多样性对高寒草甸生态系统地上净初级生产力(ANPP)的影响大于物种多样性的影响,二元线性回归显示在同时考虑二者对ANPP的影响时,可排除物种多样性的作用。但由于物种多样性下降或物种丧失引起的物种功能性状丢失或性状空间维度减小将导致功能多样性降低,表明它们之间存在一定互补性,在研究生物多样性与生态系统功能关系时,同时考虑物种多样性和功能多样性的影响仍十分必要。     

Cushion plants as critical pioneers and engineers in alpine ecosystems across the Tibetan Plateau

Cushion plants are widely representative species in the alpine ecosystem due to their vital roles in influencing abiotic and biotic environments, ecological succession processes, and ecosystem engineering. Importantly, cushion plants, such as Androsace L. and Arenaria L., are considered to be critical pioneers of ecosystem health, restoration, and sustainability across the Tibetan Plateau. This is because cushion plants (a) show tenacious vitality and can modify regional climates, substrates, and soil nutrients in extreme environments; (b) facilitate relationships with the surroundings and maintain the diversity of aboveground and belowground communities; and (c) are highly sensitive to environmental changes and thus can indicate grassland ecosystem health and resilience in the context of global change.     

Detection of Ophiocordyceps sinensis in the roots of plants in alpine meadows by nested-touchdown polymerase chain reaction

Ophiocordyceps sinensis, one of the most important income sources of rural Tibetan families, is an entomopathogenic fungus that parasitizes the ghost moth Thitarodes larvae, which live in alpine meadows on the Tibetan Plateau and in the Himalayas. The annual yield of O. sinensis has gradually declined in recent years. However, there is no effective method to sustain or increase the yield of O. sinensis artificially because the life cycle of the O. sinensis anamorph remains unclear. Here we detected O. sinensis in alpine plant roots by nested-touchdown polymerase chain reaction (PCR). Forty-two alpine plant species were screened. The roots from 23 alpine plant species (54.76 %) tested positive including 13 families and 18 genera. The detection results indicate that O. sinensis is present in the plant roots during the anamorph life cycle, to deal with harsh conditions in alpine habitats and have an increased opportunity to infect the larvae. The finding provides new information regarding the biology and ecology of O. sinensis that may be used to sustain this valuable resource.     

高寒草甸优势植物叶内、根内与土壤原核微生物群落的分异

植物内生菌具有帮助植物吸收营养元素,增强植物免疫力,抵御外界生物和非生物胁迫等功能。植物的根内和叶内存在大量的内生菌,影响着植物的健康生长。但不同植物地下(根内)和地上(叶内)内生原核微生物,以及与土壤微生物在组成和群落结构上的差异和联系还有待探索。以青藏高原高寒草甸三种优势植物青藏苔草(Carex moorcroftii)、火绒草(Leontopodium jacotianum)和高山嵩草(Carex parvula)为对象,研究了高寒草甸优势植物叶内、根内、土壤原核微生物组的组成及其与样品类型和植物类型之间的关系。结果表明:1)在门分类水平上,有13个门在土壤、叶内和根内之间有显著差异,只有5个门在不同植物之间有显著性差异,分别是变形菌门、厚壁菌门、酸杆菌门、疣微菌门以及FBP;2)在α多样性上,同种植物土壤、叶内、根内之间差异显著,而不同植物在土壤和根内差异显著,但在叶内无显著性差异;3)样品类型(叶内、根内以及土壤)是决定植物微生物组差异的最主要因子,对微生物群落变异的贡献度为20.13%;不同植物类型之间微生物群落也有显著性差异,植物类型对总变异的贡献率为14.41%,并且植...     

Seasonal patterns of root and shoot interactions in an alpine meadow on the Tibetan Plateau

Aims Numerous studies have showed that the balance between negative and positive plant–plant interactions shifted along environmental gradients. But little is known how the positive or negative plant–plant interactions varied with temporal fluctuating habitat conditions and plant ontogenetic phases.Methods In a 2-year experiment, the four perennial grasses (Kobresia humilis, Stipa aliena, Elymus nutans and Saussurea superba) were grown under four interaction treatments (no root or shoot interaction, only shoot interaction, only root interaction, root and shoot interaction). Intensity of above- and belowground interactions is proposed to vary with the fluctuation of seasonal climatic conditions and soil available nutrients. Here we report measurements of above- and belowground interactions during entire growing season. Correlation between plant interaction intensity and seasonal soil available N as well as habitat climate conditions was also performed.Important findings Our experiment found that root interactions had negative effect on plant growth for the four species during growing season. However, both negative and positive shoot interactions occurred among the four species. Despite there being shoot facilitative effect for E. nutans and S. superba, the full interaction was negative, suggested that root interaction take more important role on plant growth than that of shoot interaction. The interaction between root and shoot effect varied as a function of species identity and growth phases. The weak correlation of plant interaction intensity to habitat environmental factors suggested that plant ontogenetic characteristics may be primary factors causing temporal variation in plant interaction.     

高寒湿地和草甸退化及恢复对土壤微生物碳代谢功能多样性的影响

为研究高寒湿地、草甸的退化及恢复与土壤微生物碳代谢功能多样性的关系,以及影响土壤微生物碳代谢功能多样性的关键因素,利用BIOLOG Eco微平板法,分析了甘肃玛曲地区5类(湿地、沼泽化草甸、高寒草甸、退化草甸、人工恢复草甸) 14个退化与恢复样地的土壤微生物对单一碳源的利用情况。结果表明,从湿地到沙化草地的逐渐退化过程中,草甸的土壤微生物群落代谢活性差异显著;主要是由于在湿地干化过程中,微生物活性逐渐升高,沼泽草甸土壤微生物活性最高;随着草甸不断退化,微生物活性逐渐降低,沙化草地最低;而人工补播恢复使土壤微生物活性有所增加,表明退化对微生物碳代谢功能多样性造成显著影响,人工恢复措施在一定程度上提高了土壤微生物活性。聚合物类(吐温40、吐温80、环状糊精、肝糖)、氨基酸类及碳水化合物类是土壤微生物主要利用的碳源。冗余分析结果显示,土壤的碳氮比、含水量、有机碳、全氮、容重、氮磷比、p H及植被覆盖度是影响土壤微生物碳代谢功能多样性的关键因子。因此,可用土壤碳代谢功能多样性变化评价高寒湿地及草甸的退化和恢复及其变化程度。