Shrubs and species identity effects on the distribution and diversity of ground-dwelling arthropods in a Gobi desert

Disentangling the relationship between shrub vegetation and ground-dwelling arthropods at multiple levels of taxonomic resolution is essential to developing a suitable management strategy for the conservation of shrub-associated arthropod biodiversity in shrubland ecosystems. Using Gobi desert (dominated by shrub species Nitraria sphaerocarpa and Reaumuria soongorica) occurring widely in inland arid areas of northwest China as a model system, we sampled ground-dwelling arthropods by pitfall trapping method under canopies of both shrubs and in intershrub bare areas during spring, summer and autumn. Our aim was to determine whether the presence and species identity of shrubs influence the distribution of ground-dwelling arthropods and whether the influence of shrub presence and species identity differs among trophic and taxonomic groups. At the community level, total arthropod abundance and species richness were significantly greater under shrubs than in intershrub bare habitats, whereas more arthropods were captured under N. sphaerocarpa than under R. soongorica. At the trophic group level, the abundance of predator and decomposer arthropods was significantly greater under shrubs than in intershrub bare habitats, whereas herbivore and decomposer arthropods were more abundant under N. sphaerocarpa than under R. soongorica. At the family level, the abundance of Carabidae, Gnaphosidae, Karschiidae, Tenebrionidae and Thomisidae was consistently much greater under shrubs than in intershrub bare habitats, whereas that of Formicidae, Philodromidae and Tettigoniidae did not differ between the shrub microhabitats and the intershrub bare habitats. However, the abundance of Curculionidae under R. soongorica and the abundance of Geotrupidae under N. sphaerocarpa were significantly lower than that in intershrub bare habitats. N. sphaerocarpa was commonly preferred by arthropods in the families of Curculionidae and Tenebrionidae, whereas R. soongorica was commonly preferred by arthropods in the family Geotrupidae, but shrub species identity did not affect the abundance of the remaining families. Our results suggest that shrubs and species identity play important roles in structuring ground-dwelling arthropod communities, but the response of arthropods differed among trophic or taxonomic groups. This study may have important implications for the conservation of invertebrate biodiversity in Gobi desert ecosystems.     

Clump spacing in a desert dwarf shrub community

A Monte Carlo method based on Ripley's K function-a cumulative function related to the number of plants encountered at different distances from other plants-is used to test the null hypothesis of random distribution of shrub clumps in a desert dwarf shrub community in Namaqualand, South Africa, where Psilocaulon arenosum is the dominant shrub. The method takes into account the apparent regularity of pattern caused by the finite size (up to 2 m diameter) of the clumps. It is shown that the clump centres are significantly aggregated (compared to random expectation) at distances on the order of 1 m. Such aggregation is expected, as a simple result of regeneration near to seed sources, if the time between catastrophic droughts is short in relation to the time required for development of a non-aggregated or regular pattern determined by moisture competition. No significant regulatiry was detected at distances of 3 m or less. One subplot showed regularity above 3 m, but this pattern was not shown by the other subplot and may not be a competition effect. These results support a hypothesis of aggregation caused by regeneration pattern decaying slowly toward randomness as larger individuals compete.We thank C. J. F. ter Braak for suggesting the method of spatial analysis; 1. Noy-Meir, C. J. F. ter Braak and two unnamed reviewers for helpful comments; the Netherlands Science Research Council (ZWO) for financial support to I. C. Prentice (grant B84-218); and Prof. D. von Willert for material support to M. J. A. Werger.     

黑河中游荒漠灌丛斑块地面甲虫群落分布与微生境的关系

关于西北干旱区荒漠灌丛草地地面甲虫群落分布与微生境关系的系统研究尚鲜有报道。采用多元回归分析和RDA群落排序分析等方法,定量研究了甲虫群落分布与微生境因子的关系及其季节变异特征。多元回归分析表明,甲虫群落数量分布与土壤粗砂、中细砂和粘粉粒含量存在显著关系,3个因子解释了21%的甲虫群落变异。多元回归分析还表明,甲虫群落数量分布与春季地面/地下日平均温度和土壤含水量有显著关系(3个因子解释了32%的甲虫群落变异),而与夏季和秋季地面/地下日平均温度和土壤含水量无显著关系。RDA群落排序分析表明,土壤粗砂含量、中细砂含量、地面温度和地下温度对春季甲虫种群分布有显著的影响,解释了34.3%的甲虫种群变异;土壤粗砂和中细砂含量对夏季甲虫种群分布有显著影响,解释了18.8%的甲虫种群变异;土壤粗砂含量、地下日均温和土壤含水量对秋季甲虫种群分布有一定的影响,解释了17.1%的甲虫种群变异。Pearson相关分析表明不同甲虫种群对微生境因子的响应模式不同。主要结论是:微生境的非生物环境因子是决定荒漠甲虫群落空间分布格局的重要因子之一,但是环境因子的影响作用存在明显的季节变异,并且因种类不同而异。     

鄂尔多斯高原荒漠化草原与草原化荒漠灌木类群生物多样性的研究

研究了灌木群落生物多样性随环境梯度变化的分布特点并分析了各环境因子对群落生物多样性的影响．结果表明，灌木类群多样性取决于群落的空间配置，特别是群落的草本层组成．从荒漠化草原到草原化荒漠灌木类群的多样性逐渐减小；水分梯度变化是诸生态因子（ 地理坐标、年均温度、最冷、最热月均温、年均蒸发量、日照百分率、年均风速和年均沙暴日数等） 中对群落多样性影响最大的因子，但其显著性偏低，这主要是人类过度放牧和破坏给灌木群落的烙印远远超过了水分梯度变化的影响．     

Revegetated shrub species recruit different soil fungal assemblages in a desert ecosystem

Plant and Soil - Revegetation with xeric shrubs is a widely applied measure for restoring degraded ecosystems in the deserts of northern China. However, knowledge on the soil fungal assemblages in...     

荒漠生态系统鼠类对土壤和植被的扰动效应

干扰形成的斑块对荒漠生态系统时空异质性的维系和发展具有重要意义。鼠类作为生物干扰的重要代表,是荒漠生态系统斑块形成的主要来源,它们已从生理、形态、行为进化出一系列特点适应了荒漠生态系统的严酷环境,同时其挖掘、采食行为也深刻影响着荒漠生态系统的环境。本文主要从鼠类活动对土壤(包括土壤发生过程、土壤斑块的形成、土壤理化性质)和植物群落(包括物种多样性、生产力、植物种子)的扰动效应做了归纳总结,旨在阐明鼠类在荒漠生态系统中的作用。     

人工灌丛化对荒漠草原生态系统碳储量的影响

宁夏盐池县从20世纪70年代开始在荒漠草原上人工种植柠条灌木用以防风固沙和生态恢复,这一人为措施极大地改变了区域生态系统的植被结构和碳循环,而定量评估人工灌丛化对荒漠草原生态系统碳储量的影响,不仅能够揭示人类活动的碳循环反馈机制,而且可为地方政府生态治理提供理论指导。结合Biome-BGC模型和Logistics生长模型模拟了1958—2017年间荒漠草原人工灌丛化前后的碳储量变化,定量分析了人工灌丛化对生态系统碳储量和组分的影响。结果表明:(1)结合Biome-BGC模型和Logistics生长模型可以较准确地模拟出荒漠草原人工灌丛化过程中生态系统碳储量的变化。(2)人工灌丛化会快速改变荒漠草原的碳储量累积特征,柠条灌木种植后的快速生长阶段极大增强了生态系统的总碳储量,导致生态系统的碳储量特征由草地型向灌木型转变。(3)人工灌丛化改变了生态系统各类型碳储量的组分结构,其对地上植被和枯落物碳储量的影响非常明显,灌丛化后生态系统的植被和枯落物碳分别增加了6倍和1.76倍;因植被碳向土壤碳转化过程较慢,故人工灌丛化对地下土壤碳储量的影响在短期内较为微弱。以上结果显示,荒漠草原人工灌丛化能显...     

Influence of temporal heterogeneity in nitrogen supply on competitive interactions in a desert shrub community

Soil nutrients in arid systems are supplied to plants in brief pulses following precipitation inputs. While these resource dynamics have been well documented, little is known about how this temporal heterogeneity influences competitive interactions. We examined the impacts of the temporal pattern of N supply on competitive intensity and ability in an N-limited desert shrub community. At our field site, the three codominant shrubs, Atriplex confertifolia, A. parryi, and Sarcobatus vermiculatus, differ in seasonal growth patterns, with A. confertifolia and S. vermiculatus achieving higher growth rates earlier in the growing season than A. parryi. We predicted that these timing differences in maximum growth rate may interact with temporal variation in N supply to alter competitive abilities over time. Seedlings of the two Atriplex species were planted either individually in field plots or as target plants surrounded by neighbor seedlings. After one year of establishment, the same amount of ¹⁵N was applied to plots either as early spring pulses, mid spring pulses or continuously through the second growing season. Competitive effects were observed under continuous and pulsed N supply. Averaged across all target–neighbor treatments, competitive intensity was ∼1.8-fold greater when N was pulsed compared to when N was supplied continuously, but overall, the outcome of competitive interactions was not influenced by N pulse timing. While the timing of resource supply did not differentially influence the competitive abilities of coexisting species in this system, the temporal pattern of resource supply did alter the intensity of competitive interactions among species. While additional studies in other systems are needed to evaluate the generality of these results, this study suggests that competitive intensity may not necessarily be a direct function of productivity or resource availability as traditionally assumed. Instead, the intensity of competitive interactions in resource-poor systems may depend upon the temporal pattern of resource supply.     

Changes in ground beetle diversity and community composition in age structured forests (Coleoptera, Carabidae)

We examined diversity, community composition, and wing-state of Carabidae as a function of forest age in Piedmont North Carolina. Carabidae were collected monthly from 396 pitfall traps (12×33 sites) from March 2009 through February 2010, representing 5 forest age classes approximately 0, 10, 50, 85, and 150 years old. A total of 2,568 individuals, representing 30 genera and 63 species, were collected. Carabid species diversity, as estimated by six diversity indices, was significantly different between the oldest and youngest forest age classes for four of the six indices. Most carabid species were habitat generalists, occurring in all or most of the forest age classes. Carabid species composition varied across forest age classes. Seventeen carabid species were identified as potential candidates for ecological indicators of forest age. Non-metric multidimensional scaling (NMDS) showed separation among forest age classes in terms of carabid beetle community composition. The proportion of individuals capable of flight decreased significantly with forest age.     

Gut microbial community response to herbicide exposure in a ground beetle

Gut microbiota plays a key role in physiological processes of insects, including nutritional metabolism, development, immunity and detoxification. Environmental stressors such as herbicides, used to optimize and improve crop yields, may interfere with the mutualistic relationships causing negative consequences for the host health. Dinitroaniline herbicides, for example pendimethalin, are used worldwide in pre-emergence application to control grass and some broadleaf weeds. They target microtubules to arrest cell division and inhibit the development of roots and shoots. Effects of a pendimethalin-based herbicide were assessed on the gut microbial community of Pterostichus melas italicus Dejean, 1828 (Coleoptera, Carabidae). The exposure effect was tested in vivo by using a recommended field rate (4 L per ha, 330 gL⁻¹ of active ingredient) and evaluating the variability of responses in 21 days, corresponding to the half-life of pendimethalin. The 16S rRNA sequencing data showed that the gut lumen was dominated by Proteobacteria, Firmicutes, Fusobacteria, Tenericutes and Bacteroidetes. The exposure interfered with the bacterial community richness and diversity associated with the gut from 2 days after the treatment. The differential abundance analyses highlighted a shift involving Lactobacillaceae, Streptomycetaceae, Neisseriaceae, Ruminococcaceae and Enterobacteriaceae. An increase in species such as Enterobacter sp., Pseudomonas sp., Pantoea sp and Paracoccus sp. involved in the herbicide degradation was also recorded after 21 days of exposure. Phylogenetic investigation of communities by reconstruction of unobserved states (PICRUSt) analysis indicated that the exposure has effects on the most predicted functional categories of gut microbiota related to metabolic function including carbohydrate, amino acid and lipid metabolism. These results demonstrate that pendimethalin can impact microbial communities associated with generalist predators inhabiting croplands leading to severe implications for the species’ ecological role. Understanding the effects of herbicides such as pendimethalin on ground beetles may help to protect beneficial soil insects that have a crucial role in the ecosystem services.     

Hydrated mucilage reduces post-dispersal seed removal of a sand desert shrub by ants in a semiarid ecosystem

Post-dispersal seed removal by animals can lead to extensive seed loss and thus is an important factor in structuring plant communities. However, we know much less about post-dispersal seed predation than about other forms of herbivory. Mucilage plays many ecological roles in adaptation of plants to diverse environments; nevertheless, until now the role of mucilage in ant-mediated seed movement remains largely hypothetical. We studied the role of mucilage in seed removal of Artemisia sphaerocephala by ants in Mu Us Sandland in Inner Mongolia, China. Messor aciculatus was the most active seed predator of Artemisia sphaerocephala. Time to first ant collecting (T _1st) of wet intact seeds was longest and significantly different from that for dry intact seeds, wet demucilaged seeds, and dry demucilaged seeds; number of seeds removed to ant nests was lowest for wet intact seeds. After they were collected by ants, 5 % of wet intact seeds were dropped during transport. Our results indicate that seed mucilage of Artemisia sphaerocephala may play a significant role in post-dispersal seed removal by (1) making seeds less attractive to ants, thus resulting in a delay of collection time; (2) forming a strong bond to soil particles, making it difficult for ants to remove seeds; and (3) making seeds more likely to be dropped during transport, thereby allowing them to escape from predation even after collection by ants. This study demonstrates the importance of mucilage in reducing seed removal by ants and thus in anchoring seeds of desert plants in the vicinity of mother plants.     

Effect of protection and controlled grazing on the vegetation of a Mediterranean desert ecosystem in Northern Egypt

The present study provides preliminary assessments of the effect of protection and controlled grazing on the vegetation composition and phytomass in a Mediterranean desert ecosystem, 80 km W of Alexandria.Plots were fenced in 1974 and 1977, and different degrees of grazing pressure (no grazing, 25 and 50% of the grazing pressure freely practiced by the inhabitants) were applied. Changes in density, cover, frequency, phytomass and the phenological sequence of species were recorded and compared to those of the same species outside the fenced plots.Density and cover of perennials, frequency and presence of annuals, and total phytomass increased as a result of protection and controlled grazing. The arrangement of stands along ordination axes correlated with the degree of grazing pressure, which indicated that the distribution of species in the study area was more related to overgrazing than to the factors of the physical environment.Nomenclature of vascular plants follows Täckholm, V., Student's Flora of Egypt, Cairo University Press, 1974.This study was carried out within the framework of the Project of Regional Environmental Management of Mediterranean Desert Ecosystems of Northern Egypt (REMDENE), sponsored by the Egyptian Academy of Scientific Research and Technology, and supported by grants from the USA Environmental Protection Agency and the Ford Foundation.     

Influences of frost-heaving on vegetation and nutrient regime of polygon-patterned ground

Actively frost-heaved polygon ground in an alpine area of nutrient-poor shrub heaths, had a large number of basophilous vascular plant species and cryptogams. The soils of the polygons had much higher concentrations of extractable plant nutrients and higher pH values than the surrounding stable ground, probably due to mixing of soils, intense weathering of the raw soil and lack of podzolization under conditions of high frost activity. Plant distribution was correlated to the intensity of frost-heaving; basophyte dominance was consistent with high pH and high extractable nutrient levels on the most actively upheaved polygon centres, whereas heath vegetation became increasingly dominant towards polygon borders with weaker activity, and on polygons with weak recent activity. Empetrum-heath species, usually distributed at sites with thin snow cover during winter, seemed better adapted to weak frost-heaving than species characteristic of communities normally developed in places with medium snow cover.     

The effects of harvester ant (Messor ebeninus Forel) nests on vegetation and soil properties in a desert dwarf shrub community in north-eastern Arabia

In desert ecosystems, harvester ants have been shown to be important granivores and seed dispersers. Because many desert plants exist as seeds in the ground for long periods, harvester ants may greatly influence plant population dynamics. In this study, we examine the effects of harvester ant nests on vegetation and soil properties in a desert ecosystem dominated by the dwarf shrub Rhanterium epapposum in Kuwait, north-eastern Arabia. Soil properties were greatly modified in the circular refuse zone around the nests of the harvester ants, with elevated levels of nutrients (except nitrogen) and organic matter. Plant species richness and productivity were also significantly enhanced in the refuse zone. The vast majority of species inhabiting this zone were desert annuals, but there is no evidence to suggest that the species involved have any distinct association with ant nests. Harvester ants therefore contribute substantially to small-scale spatial heterogeneity in this aridland plant community. It is also suggested that the significance of ant nests in providing favourable sites for plant growth is enhanced in drier years, when many species in off-nest sites may die prematurely due to drought. Furthermore, because ants occasionally abandon their nests and create new colonies, the addition of nutrient-rich patches to the landscape over time could represent an important mechanism for maintaining fertility of desert soils, possibly with long-term implications for plant biodiversity. Harvester ants can therefore be regarded as a key ecosystem engineer in this relatively undisturbed desert ecosystem of Kuwait.     

Species and plant community distribution in a Mojave-Great Basin desert transition

Multivariate analyses were used to describe the vegetation characteristics of a transition from lowelevation Mojave desert to higher-elevation Great Basin desert. Vegetation data used were from Plutonium Valley in the Nevada Test Site. Data from forty nine releves were analyzed with two classifications (two-day indicator analysis or TWINSPAN and unweighted paried group cluster analysis or CLUSTER). Three ordinations, reciprocal averaging (RA), detrended reciprocal averaging (DCA) and non-metric multidimensional scaling (MNDS), were also used. A rotational correlation analysis was used to determine the vector direction of environmental gradients that correlate best with ordination results. Only token correspondence was found between multivariate classes generated by TWINSPAN and CLUSTER, and seven classes (plant communities) identified from field reconnaissance. The latter seven communities were based on differences in dominant species. Distribution of the vegetation was related more to beta diversity than alpha diversity. Individual species were much less diagnostic than the amount of plant cover, groups or guilds of species or differences in elevation and steepness of slope. Because of the high beta diversity the NMDS ordination gave results with the greatest ease of interpretation.     

Influence of vegetation structure on the small mammal community in a shortgrass prairie ecosystem

The structure of vegetation, and how this structure varies across a landscape, is crucial to understanding the distribution of wildlife species. Between 2002 and 2004, we sampled small mammal communities and measured vegetation structure at 185 locations across a range of disturbance regimes in a shortgrass prairie ecosystem in southeastern Colorado, USA. At each sampling location, the local disturbance regime was some combination of varying intensity of livestock grazing, military training activity, and fire. Vegetation structural characteristics measured included percent bare ground, basal cover, litter, shrub density, and mean grass and shrub height. Rodent communities were described by richness, diversity, total and per capita biomass, and species abundances. Northern grasshopper mice (Onychomys leucogaster), Ord's kangaroo rats (Dipodomys ordii), silky pocket mice (Perognathus flavus), western harvest mice (Reithrodontomys megalotis), white-footed mice (Peromyscus leucopus), southern plains wood rats (Neotoma micropus), thirteen-lined ground squirrels (Spermophilus tridecemlineatus), deer mice (Peromyscus maniculatus), and spotted ground squirrels (Spermophilus spilosoma) accounted for >99 % of all captures. Canonical correlation analysis was used to assess the relationship between small mammals and vegetation structure. The first two canonical variates explained over 50 % of the variation in vegetation structure and were related to the ratio of bare ground to basal coverage and litter accumulation. Rodent community indices were most strongly related to litter accumulation and shrub density, though the models had low explanatory power. Our results agreed with published findings regarding microhabitat associations and indicated small mammal communities benefited from a system of interacting disturbances and the resulting landscape mosaic.     

Factors influencing above‐ground and soil seed bank vegetation diversity at different scales in a quasi‐Mediterranean ecosystem

Questions

Are factors influencing plant diversity in a fire‐prone Mediterranean ecosystem of southeast Australia scale‐dependent?

Location

Heathy woodland, Otways region, Victoria, southeast Australia

Methods

We measured patterns of above‐ground and soil seed bank vegetation diversity and associated them with climatic, biotic, edaphic, topographic, spatial and disturbance factors at multiple scales (macro to micro) using linear mixed effect and generalized dissimilarity modelling.

Results

At the macro‐scale, we found species richness above‐ground best described by climatic factors and in the soil seed bank by disturbance factors. At the micro‐scale we found species richness best described above‐ground and in the soil seed bank by disturbance factors, in particular time‐since‐last‐fire. We found variance in macro‐scale β‐diversity (species turnover) best explained above‐ground by climatic and disturbance factors and in the soil seed bank by climatic and biotic factors.

Conclusions

Regional climatic gradients interact with edaphic factors and fire disturbance history at small spatial scales to influence species richness and turnover in the studied ecosystem. Current fire management regimes need to incorporate key climatic–disturbance–diversity interactions to maintain floristic diversity in the studied system.

     

沙漠前沿不同植被恢复模式的生态服务功能差异

沙漠是具有生态脆弱性和生态功能特殊性的生态系统,其生态系统的恢复与重建,更多的是考虑其防风固沙、生物多样性的产生与维持、气候调节、土壤保护等非实物型生态服务功能的发挥。根据植被样地调查、土壤分析和风因子监测等相关数据,开展了新疆奇台县沙漠前沿不同植被恢复模式的生态服务功能差异研究。结果表明:人工植被恢复模式较天然植被恢复模式对风速和风动能的消抵作用明显,人工植被恢复区比天然植被恢复区多58.8 d/a无风天;年均降低风速0.88 m/s,消抵65.2%的风动能,人工植被恢复对北向和西北向风的消抵作用最显著,对西南向风的消抵作用最弱;不同植被恢复模式的生物多样性保育功能差异较大,天然植被恢复的植物群落较之人工植被恢复的植物群落,物种丰富度指数和Shannon-Wiener指数更高,Pielou指数则相对较低,天然恢复的植物群落的稳定性更高,其维持、繁衍和保持植物多样性的能力更强;不同植被恢复模式对土壤部分化学性质的影响有明显差异,人工植被恢复模式能够通过植物的生理代谢,降低沙漠前沿土壤的含盐量和pH值,但对土壤有机质含量影响不显著。上述研究结果可以为高效的沙漠前沿植被恢复模式的筛选提供必要的理论支撑。     

Microbial community structure and diversity in a native forest wood-decomposed hollow-stump ecosystem

The aim of this study is to investigate the microbial community structure and diversity in a wood-decomposed hollow-stump ecosystem. Microbial communities of SD-1, a lateritic soil sample from forest hollow-stump ecosystems in Fuzhou (a southeastern coast city of China), were characterized by constructing and analyzing rRNA gene clone libraries. Sixty-six phylotypes were identified from 112 bacterial clones, including Acidobacteria (71.5%), Proteobacteria (24.1%) and Verrucomicrobia (0.9%). A total of 40 phylotypes were obtained from 138 fungal clones, including Basidiomycota (42.8%), Ascomycota (36.2%), Zygomycota (13.8%), Chytridiomycota (2.9%) and Fungi incertae sedis (4.3%). The results showed a variety of clones related to the reported lignocellulose-decomposing microorganisms. They included some important bacterial decomposers, such as Sphingomonas and Burkholderia, and a number of wood-decaying fungi, including Tricholomataceae, Strophariaceae and Agaricaceae of Basidiomycota; Orbilia, Aspergillus, Phialocephala, Epicoccum and Phoma of Ascomycota and Mucorales of Zygomycota. The result indicated that the lignocellulolytic microorganisms worked synergically with a unique community structure to biodegrade lignocellulose in the hollow-stump ecosystem.