盐度对滨海土壤细菌多样性和群落构建过程的影响

滨海盐土是重要的农业土地后备资源.微生物是土壤中物质循环的关键动力,然而盐度对土壤微生物群落特征影响的研究还很缺乏.本研究采集滨海地区的土壤样品,研究非盐、轻盐和高盐3组不同盐度对土壤细菌数量、多样性和群落构建的影响.结果表明:与非盐和轻盐土壤相比,高盐土壤的脱氢酶活性和细菌数量显著降低,而细菌α多样性没有变化,细菌群...     

Coexistence and geographical distribution of Leguminosae in an area of Atlantic forest in the semi-arid region of Brazil

Understanding the factors that affect plant species distribution and coexistence in areas with high plant species diversity is a challenge for ecologists.According to some authors,species occupy specif...     

Spatial Distribution and Coexistence Patterns of Caddisfly Larvae (Trichoptera) in a Hungarian Stream

It is well known that stream macroinvertebrates usually show aggregated spatial distributions caused by extrinsic factors and interactions among species and individuals. In the present study, the spatial distribution of caddisfly assemblages and coexistence patterns of larval caddisfly species (Insecta: Trichoptera) were measured in a Hungarian stream reach at three different spatial scales. Caddisfly assemblages showed aggregated, random and regular distributions as measured by the variance‐mean relationship of species richness as sampling area increased from 0.0225 m² to 0.2025 m². The observed coexistence patterns indicated interactions (lower diversity of unique species combinations than expected by chance) among species for aggregated distributions. These interactions among species proved to be positive associations particularly among species belonging to the same functional feeding group. The positive associations and the aggregated distribution of caddisflies supported the hypothesis that microhabitat patches (patchy microhabitat‐macroinvertebrate model) and/or positive biological interactions among species using the same resource (hypothesis of facilitation) have a deterministic effect on the spatial distribution of caddisfly assemblages. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Coexistence and geographical distribution of Leguminosae in an area of Atlantic forest in the semi‐arid region of Brazil

Abstract Understanding the factors that affect plant species distribution and coexistence in areas with high plant species diversity is a challenge for ecologists. According to some authors, species occupy specific niches, but for others, species coexistence and geographical distribution patterns are random. Floristic composition of the family Leguminosae was studied on moist and dry slopes of the Baturité mountains in semi‐arid northeastern Brazil and was compared with findings for other plant formations elsewhere in Brazil. Substantial floristic differences were found between the moist windward and dry leeward slopes of the Baturité mountains despite their close geographical proximity. The leeward slope was slightly more diverse than the windward slope. Similarity analyses showed that the windward face is floristically allied to the Amazon forest, whereas the leeward slope is similar to other dry‐area formations of northeastern Brazil, such as thorny woodland (caatinga) and seasonal forests. The strong floristic differences that were observed between the windward and leeward slopes corroborate the theory of ecological niche conservatism, which holds that species occurrence is closely linked to environmental factors, such as temperature and precipitation.     

Spatial heterogeneity of mortality and temporal fluctuation in fertility promote coexistence but not vice versa: a random-community approach

Both spatial heterogeneity and temporal fluctuation of the environment are important mechanisms promoting species coexistence, but they work in different manners. We consider many pairs of species with randomly generated survivorship and fertility in the lottery model, and examine how the variability in demographic processes affects the outcome of competition. The results are: [1] Coexistence is easier if habitat difference in mortality is greater, or if year-to-year variation in reproductive rate is larger. But neither habitat-difference in fertility nor temporal variation in mortality promotes coexistence. [2] Mean fertility does not affect the outcome if CV remains constant. In contrast, enhanced mean mortality decreases the fraction of coexisting pairs if the environment fluctuates temporally. [3] We also investigate the effect of limited dispersal of propagules between habitats. Compared with the complete mixing case, the fraction of coexisting pairs is clearly enhanced if the spatial heterogeneity is the major source of environmental variation, but shows slight increase if the temporal fluctuation is dominant. We conclude that spatial heterogeneity is likely to work more effectively in promoting species coexistence than temporal fluctuation, especially when the species suffer relatively high mortality, and disperse their propagules in a limited spatial scale.     

Shoot pruning of a hedgerow perennial legume alters the availability and temporal dynamics of root-derived nitrogen in a subtropical setting

There is increasing interest in the ecology of tree-based intercropping systems, particularly alley cropping, in temperate settings. Shoot pruning of the tree component is an integral practice to alley cropping. Shoot pruning likely results in an input of belowground C and N to soil, with potential, but unknown impacts on the time pattern of N availability. We evaluated the impacts of pruning of Amorpha fruticosa L. on (a) its root dynamics; (b) mineral N and microbial N, and (c) the fate of root-derived N and its importance in determining N availability. For this, we conducted repeated partial pruning and foliar labeling with ¹⁵N under field conditions in Georgia, USA. Pruning altered root dynamics by initially decreasing biomass and later preventing increases, likely due to root death. Pruning modified the time pattern of mineral N by substantially increasing concentrations during the 3?months following pruning. ¹⁵N labeling indicated that root-derived N was an important source of this extra N and that pruning caused the availability of root-derived N to microbes to be extended until the following growing season. Greater concentrations of mineral N, a greater pool of microbial N and prolonged microbial access and storage of root-derived N with pruning has the potential to positively impact system productivity.     

Spatial patterns of a savanna palm tree Borassus aethiopum and its temporal variability

The spatial distributions and associations of plant species in a stand can provide essential information about their dynamics. However, since tree spatial distribution and association depend on factors that operate at different scales, disentangling the effects of environmental heterogeneity and plant–plant interactions requires the choice of a suitable null model for spatial analysis. We analyzed the spatial distributions of the same savanna palm tree populations that were studied, the underlying hypothesis being that these distributions have changed in 20 years. To remove the effect of large-scale environmental heterogeneity, the inhomogeneous L-function under the heterogeneous Poisson null model was used. We showed: (i) unlike 20 years ago, adults had a regular distribution instead of an aggregated distribution in the grass savanna; (ii) although the spatial distribution of seedlings and juveniles was always aggregated, we observed a decrease in the size of the aggregates (intensities); (iii) except for juveniles, no other stages were associated with nutrient-rich patches, which was also different 20 years ago; (iv) we did not observe any particular difference in structure between two study sites, only that female palm trees were spatially associated with entire-leafed seedlings in the reserve while they were spatially independent in the rural area. Our study supports the hypothesis that the spatial distributions have partially changed, and that the management of spatial heterogeneity has improved and given more precision in the results.     

Effects of grazing and ant/beetle interaction on seed production in the legume Vicia sepium in a seminatural grassland

Abstract.  1. Seed production can be affected by cattle grazing, insect herbivores, and seed predators. Bush vetch, Vicia sepium L. (Fabaceae), possess extra floral nectaries (EFNs), which can attract ants that act as plant defenders.
2. In this field study, four different manipulations were used to investigate interactions between V. sepium , ants, aphids, and seed predators, mainly Bruchus atomarius. The experiment was set up in grazed and non-grazed plots in a semi-natural grassland in south-central Sweden.
3. Grazing negatively affected number of V. sepium buds, flowers, and pods. Seed set, defined as the number of developed seeds per number of ovules in a pod, was higher in grazed plots. Ant abundance, however, was not affected by grazing. Ten different ant species were found on V. sepium and the number of ants was positively correlated with the presence of EFNs. Aphids were found only when ants were excluded from the plants. Pod and seed production of V. sepium plants was not affected by the presence of ants. The seed predator B. atomarius was not affected by the presence of ants. No support was found for the supposition that V. sepium benefited from attracting ants by producing extra floral nectar.
4. A small observational study of V. sepium plants in shrub ( Rosa dumalis ) plots compared with grassland plots was added to the experimental study . Vicia sepium plants were longer and had higher seed-set (seeds/ovules) in shrub plots than in grassland plots.     

Geographic and temporal variation in the ant–seed dispersal assemblage of the perennial herb Helleborus foetidus L. (Ranunculaceae)

Spatio-temporal variations in the composition of the animal interactive assemblages may result in variations in selective pressures on the plants. In ant–seed dispersal mutualisms, the study of the magnitude of spatial and temporal variation of ant assemblages is rarely studied, limiting inferences and generalizations on the evolution of this mutualism. Here, we describe the ant–disperser assemblage of the myrmecochorous herb Helleborus foetidus in 14 populations across the Iberian Peninsula, and dissect the variation in the assemblage into spatial and temporal components as a first step to evaluate the evolutionary potential of this interaction. The ant–visitor assemblage of H. foetidus was mainly represented by species of Formicinae and it was highly diverse and variable in composition and function. Ants behaving as legitimate dispersers and those with mixed behaviour numerically dominated the assemblage compared with elaiosome consumers. The magnitude of the spatial variation was higher than the temporal variation, suggesting that the relative frequency of each functional group will be more foreseeable among years in each population than among populations. At the expense of further analysis of the effects of such variation on dispersal success, we can envisage a selection mosaic scenario, where local adaptive responses of plants might arise as a result of local variations in the specific composition and function of the assemblage.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 92 , 135–150.     

Spatial and temporal overlap of caracal and serval in Serengeti National Park,Tanzania

Understanding activity and habitat use are important for identifying mechanisms facilitating species co-occurrence. We studied habitat use and activity patterns of caracals (Caracal caracal) and servals (Leptailurus serval), primarily nocturnal, mid-sized felids that prey extensively on small mammals and co-occur in portions of sub-Saharan Africa. Spatial and temporal patterns of segregation were investigated in a 1,085-km² area of Serengeti National Park, Tanzania from 2010–2012. We used occupancy analysis to quantify habitat use and kernel density estimators and Mardia–Watson–Wheleer tests to analyse activity patterns. We found evidence for habitat divergence but high temporal overlap between species. Servals selected for grassland and avoided shrubland and wooded grassland. In contrast, the findings showed that caracals avoided grassland and woodland–shrubland; however, 73% of caracals were detected in wooded grassland. Overall, caracals and servals co-occurred independently, Species Interaction Factor, (phi = 1). This indicates that differential use of habitats in part facilitated coexistence of caracals and servals. Proper management of the declining grasslands including other habitats are recommended to facilitate continued coexistence. Additional studies, including feeding ecology, would be important to further understand mechanisms facilitating coexistence between caracals and servals.     

Spatial and temporal abundance,substrate partitioning and species co-occurrence in a guild of Neotropical blackflies (Diptera: Simuliidae)

Blackfly larvae were sampled monthly from two smallNeotropical mountain streams 500 m apart from each other in northernVenezuela during a 15-month period, and ten habitat variables weremeasured at two altitudes (800 and 900 m) to determine local spatialand temporal variations in abundance, stream variables, speciesco-occurrence, and substrate preference within the blackflyguild. The blackfly species composition of each stream was the same,with five species (in order of abundance): Simulium ochraceumWalker s.l., S. paynei Vargas, S. metallicum Bellardicytospecies E, Simulium sp., and S. horacioi Okazawa &Onishi. There were clear differences in community structurebetween streams (not among altitudes), although S. ochraceums.l. was the most abundant species in both habitats. Principal component andcorrelation analyses revealed that structural (great depth, width,flow, and discharge) and chemical (low conductivity) factors werethe stream variables best associated to the spatial distribution ofmost blackfly species. Blackfly abundance was greater in the largerstream. Larvae were most abundant on submerged rocks and fallenleaves, although the patterns of substrate use within the guildrevealed substrate partitioning among most blackfly species.There was one general annual peak of abundance at the end of therainy season. We suggest that blackfly community structure in theseNeotropical headwaters streams, over the small spatial scaleexamined here, is largely influenced by interactions among streamsize and velocity-related factors (width, streamflow, discharge andsubstrate availability-stability) and the rainfall regime.     

人工红松林步行虫(Coleoptera:Carabidae)群落物种共存格局动态分析

揭示群落物种共存格局是群落生态学研究的重点内容之一,零模型的应用极大的促进了群落物种共存格局及其调控机制的进展,然而针对地下生物群落共存格局动态特征的研究并不多见。在帽儿山森林生态站的人工红松林内,通过5次调查取样基于零模型模拟分析小尺度空间(20 m×20 m)步行虫群落物种共存格局的动态特征。结果表明:(1)共捕获步行虫20种,2278只个体,其中Carabus billergi maoershanensis为所有调查季节数量最具优势且分布最广泛的物种,步行虫群落结构具明显的时间变异性;(2)2013年6月步行虫群落为集群性共存格局,而2014年8、10月为竞争性共存格局,基于目前的零模型指标和法则难以准确揭示其他月份是集群性还是竞争性的共存格局,但所有季节的群落均表现为明显的非随机性共存格局,这些共存格局的发现并不完全支持Diamond的群落构建机制理论;(3)所有调查季节均发现很少的显著物种对,基于更严格的检验表明群落中集群性物种对多于隔离性物种对,那些表现为显著的非随机性共存关系的物种对往往是群落内数量较大且分布广泛的优势和常见物种。表明非随机性共存格局可能是帽儿山人工红松林小尺度空间步行虫群落的常见格局,这种非随机性格局具一定的短期动态稳定性,但不同季节这种非随机性共存格局类型表现不同,群落内这些较少的显著物种对可能对群落物种共存格局具有一定的贡献。     

Spatial distribution and temporal dynamic of the seed pool in a Danish lowland stream

In this paper we quantify the seed pools in four locations down through a small stream in Denmark. The objectives of the study were (1) to test if the number of plant taxa in the seed pool increases downstream in the stream system; (2) to test if the seed density in the pool is highest in autumn; and (3) to analyze to what extent the seed pool contributes to re-establishment of vegetation in spring. Counting method showed no increase in species taxa in the seed pool down through the stream system. Neither did we find clear seasonal patterns in seed abundance in the seed pool. By concurrent field and laboratory observations in spring we found that seed pools can function as a source for re-establishing the vegetation in spring. However, the actual germination rate in the field was <100 and <10 times the germination rate in the laboratory for aquatic and terrestrial plants, respectively. The results suggest that small lowland streams contain large seed pools in deposition areas throughout the year, and that seed pools are much more important for the re-establishment of riparian stream vegetation in spring than submerged vegetation.     

Untangling the mechanisms of cryptic species coexistence in a nematode community through individual-based modelling

Cryptic species are morphologically identical but genetically distinct, and are prominent across numerous phyla. The coexistence of such closely related species on local scales would seem to run counter to traditional coexistence and competition theory; it has been hypothesized as a consequence of differences in their resource use or tolerances to environmental conditions. We developed an individual-based model of a community of three cryptic Litoditis marina (nematode) species, to understand how individual-level interspecific and intraspecific interactions might explain the coexistence of these closely related species. The model incorporates individuals' reproduction, competition, dispersal and resource use. Data characterizing the cryptic species (growth rates, dispersal ability, competitive interactions and responses to changing environmental conditions) were obtained from laboratory experiments involving both mono- and multispecific nematode cultures, and are used to parameterize the model. Simulation studies are used to investigate which individual-level mechanisms of dispersal and interaction lead to the characteristic population-level patterns observed experimentally. Our results highlight the key role of intraspecific competition in mediating dispersal and therefore co-occurrence of the cryptic species. The differences in dispersal also influence the response of the cryptic species to competition, a combination of factors that provides an explanation for their co-occurrence. These results provide insights into how changes in individual-level processes can be amplified to affect population-level co-occurrence.     

灵山湾国家森林公园刺槐林下垂序商陆种子雨时空动态

垂序商陆(Phytolacca americana)的入侵给山东省沿海防护林的生物多样性及乔木更新造成了严重的危害, 为揭示其繁殖特性和扩散机制, 在灵山湾国家森林公园刺槐(Robinia pseudoacacia)林下由林缘至林内60 m设置5个梯度, 采用机械布点法对垂序商陆的结实量、种子雨分布和扩散格局进行了调查。结果表明: 1)垂序商陆的结实量与种子雨量由林缘至林内逐渐减小, 分别为2 273-1 846和1 382-621粒·m^-2, 不同空间种子雨密度占结实密度的60.80%-33.64%, 平均为49.52%, 人为搂割及动物取食是种子雨量损失的主要原因; 2)种子雨始于9月中旬, 林缘种子雨的发生早于林内, 种子雨的平均强度由林缘至林内逐渐减小, 在10月下旬和12月中旬各有一次种子雨高峰, 最大强度分别为32-4和59-5粒·m^-2·d^-1; 3)种子雨由林缘至林内散布范围逐渐减小, 同时随距母株距离的增加而减小, 其中最大散布距离与加权平均距离分别为210-180 cm和94.32-63.03 cm, 整体加权平均距离为81.00 cm。表明垂序商陆种子雨具有明显的时空异质性, 对预测其扩散潜力及群落结构组成趋势有重要的意义。