Alternative stable states and regional community structure

Many models of local species interactions predict the occurrence of priority effects due to alternative stable equilibria (ASE). However, few empirical examples of ASE have been shown. One possible explanation for the disparity is that local ASE are difficult to maintain regionally in patch dynamic models. Here we examine two possible mechanisms for regional coexistence of species engaged in local ASE. Biotically generated heterogeneity (e.g., habitat modification that favors further invasion by conspecifics) results in regional exclusion of one species at equilibrium. In contrast, abiotic heterogeneity due to spatial variation in resource supply ratios generates local-scale ASE and ensures regional coexistence with sufficiently broad environmental gradients. Abiotic heterogeneity can result in a species that is the dominant competitor over some of its range being excluded if the area where it is dominant is too small. Biotic heterogeneity can lead to alternative stable landscapes or regional priority effects, while abiotic heterogeneity results in regional determinism. Broad environmental gradients in resource supply favor regional coexistence of species that exhibit local ASE.     

Methylation of the Putative Tumor Suppressor Gene RASSF1A in Primary Cervical Tumors

Methylation-sensitive restriction endonuclease analysis (MSRA) followed by polymerase chain reaction (PCR) have been used to estimate the methylation level of 13 CpG dinucleotides in the promoter region of the putative suppressor gene RASSF1A (3p21.31) in squamous cell carcinomas of the uterine cervix (SCCs) carrying human papillomavirus (HPV) types 16, 18, and related types. Methylation of 3 to 13 CpG pairs has been found in 64% (25 out of 39) tumor DNA samples, 22% (2 out of 9) DNA samples from morphologically normal tissues adjacent to the tumor (P = 0.0306), and two out of three DNA samples from peripheral blood leukocytes of carcinoma patients. These CpG pairs are not methylated in the DNA of leukocytes of healthy donors (0 out of 10). The methylation level of the RASSF1A promoter region studied in tumors of the patients with regional lymph node metastases is significantly higher than in tumors of the patient that have no metastases (P = 8.5 × 10^–12). The methylation frequency of gene RASSF1A is two times higher than the frequency of hemi- and homozygous deletions in the chromosome 3 region where the gene is located. The data obtained indicate that methylation is one of the main mechanisms of the RASSF1A gene inactivation in HPV-positive human cervical tumors. The methylation of this gene may be an early event in the genesis of cervical tumors, the methylation level increasing with tumor progression.     

Ephemeroptera,Plecoptera, and Trichoptera on Isle Royale National Park,USA, compared to mainland species pool and size distribution

Extensive sampling for aquatic insects was conducted in the orders Ephemeroptera (mayflies), Plecoptera (stoneflies), and Trichoptera (caddisflies) (EPT) of Isle Royale National Park (ISRO), Michigan, United States of America, during summer 2013. The island was ice covered until 8,000 to 10,000 years ago and is isolated by 22–70 km distance from the mainland. Two hypotheses were examined: that ISRO EPT richness would be much reduced from the mainland, and that the species colonizing ISRO would be of smaller size than mainland, adults presumably using updrafts to bridge the distance from mainland sources. Data sets were developed for known mainland EPT species and size for those species. The first hypothesis was confirmed with the mainland species pool consisting of 417 EPT, while ISRO is known to support 73 species. Richness of EPT is directly related to the number of specimens examined. Small streams supported five EPT species, while 15–25 species were found in larger streams. Lakeshores had intermediate diversity. The second hypothesis was substantiated for stoneflies, but not for mayflies or caddisflies. Stoneflies apparently are poorer fliers than either of the other two orders.     

Systematics of Pseudorchis albida s.l. (Orchidaceae) in Europe and North America

In Scandinavia Pseudorchis albida (Orchidaceae)usually divided into the lowland and subalpine P. albida s.s. and the more or less alpine P. straminea. There have been some uncertainties and conflicting views concerning die taxonomic treatment of diese taxa. To address this issue, herbarium specimens of P. albida s.l. were studied for variation in morphological characters. A small-scale population study approach was used, as herbarium sheets with two or three plants were used as population samples. Canonical Variates Analysis (CVA) indicated a distinction between taxa in population means, corresponding to P. albida s.s. and P. straminea , respectively. Principal Components Analysis (PCA), however, revealed an overlap between individuals of the two taxa. The PGA analysis, furthermore, revealed that the overlap was considerably larger in material from Central Europe man in material from Fennoscandia. Student t -tests on separate characters confirmed the picture, wim more characters significantly different in Fennoscandian than in Central European material. Furthermore, a Tukey-Kramer test revealed that there were small differences between regional populations of P. albida s.s. , while there were several significant differences in single characters between the Norm American regional population of P. straminea , as compared with the Central European and Fennoscandian regional populations. In Central Europe there is no clear separation between taxa, while in Fennoscandia the taxa are more clearly separated. This probably means that there is a difference in the time of establishment in the different regions. The author suggests a distinction of taxa at the subspecies level, and argues that the clear distinction seen in Fennoscandian material is due to separate immigration histories for die two subspecies into Fennoscandia after the last period of glaciation.     

AMMI模型在旱地春小麦稳定性分析中的应用

基因型与环境的互作(GEI)决定了作物在多变环境下性状的稳定性。AMMI模型是一种将方差分析和主成分分析结合于一体,能更有效分析GEI、进而评价基因型稳定性和环境对基因型差异分辨力的有力工具。利用AMMI模型对10个品种(系)、13个试点组成的全国旱地春小麦区域试验产量资料分析表明,试点间平均产量变幅为396.6~4050.2 kg.hm-2,现代品种间的平均产量变幅为1318.6~2315.6 kg.hm-2;基因型间、环境间和GEI引起的产量变异达到极显著水平,三者的变异平方和分别占总处理平方和的6.2%、70.3%、23.5%,表明环境和GEI对产量变化的影响远大于基因型。用前3个代表了90.8%GEI信息的显著主成分计算基因型稳定性参(Di)和试点分辨力(Dj),基因型间Di最大相差达3倍、而试点间Dj最大相差19倍;属于高产、稳产的品种有:定西35、西旱1号、定丰889,而在这两方面均表现最差的品种为蒙麦35号。有些品种对某些试点有特殊适应性,局部推广价值也大。     

农田灌溉对印度区域气候的影响模拟

为满足人类对粮食的需求,全球灌溉农田面积迅速扩张,农田灌溉对区域气候的影响引起广泛地关注。利用区域环境系统集成模式(RIEMS2.0)和最新的土地利用变化资料,选取农田灌溉面积最大的印度区域作为研究区域,进行雨养农田和灌溉农田的对比试验,探讨农田灌溉对区域气候的影响。结果表明:(1)农田灌溉使得印度区域年平均气温降低1.4℃,年平均降水率增加0.35mm/d。农田灌溉对印度区域气候的影响存在明显的季节波动,季风前期及6月份该区域气候对下垫面变化的响应最为敏感;7-9月各气候要素变化较小。(2) 农田灌溉使得印度区域地表净辐射增加,且地表净辐射在潜热通量和感热通量之间的分配发生了较大的改变,潜热通量增加,感热通量减少;对地表起冷却作用;同时由于土壤湿度增加,蒸散作用增强,大气中水汽含量增加,潜热不稳定能量增加,导致对流性降水增加。     

Species–area curve and distance–decay relationships indicate habitat thresholds of ectomycorrhizal fungi in an old‐growth Pseudotsuga menziesii landscape

Aim

Ectomycorrhizal fungi (EMF) are a diverse and essential biota of forests that are vulnerable to species loss through reductions in late‐seral habitat. We examined how the spatial ecology of this biota, particularly distance–decay and species–area relationships, could better inform habitat thresholds for EMF conservation planning.

Location

Southeast Vancouver Island near Victoria, British Columbia, Canada.

Methods

Using a stratified sampling design, 11 plots (0.15 ha in size) were established at 0.05–17.5 km apart across 2,800 ha of mesic old‐growth Pseudotsuga menziesii var. menziesii and Tsuga heterophylla forests. EMF communities were compiled through molecular analysis of root tips and sporocarps.

Results

The EMF community was comprised of many Cortinarius, Piloderma, Russula and Tricholoma species typical of mesotrophic habitat. A total of 238 EMF species were observed, of which 86 species were detected only once. The ratio of average species richness per plot (84 taxa) to total richness was low at 0.35, and inherent stochasticity of the EMF community was estimated to be 31% community dissimilarity for species incidence. Distance decay of EMF communities was nonlinear, with an estimated slope break at 2.6 km, followed by a largely unchanging trend in β‐diversity. Accumulated species–area curves were fitted best by the cumulative Weibull sigmoid model, and the asymptote (367 species) at approx. 50 ha was consistent with nonparametric estimates of γ‐diversity (342–362 spp.).

Main conclusions

Old‐growth forests host an impressive amount of EMF diversity, and many of the Ramaria, Inocybe and Russula species are likely to be endemic to the Pacific Northwest. Both niche‐ and neutral‐based processes influenced EMF community composition, resulting in a minimum threshold of 50 ha (1.8% of the sample area) for capturing γ‐diversity. These spatial patterns will help design and evaluate conservation efforts, such as retention forestry, to sustain fully diverse EMF communities over managed landscapes.

     

Crop production structure and stability under climate change in South America

Southern South America is expected to play an increasingly important role in global food production, but climate change could seriously threaten it. Here we have analysed long‐term historical data for major crops (rice, oats, barley, sunflower, soybean, sorghum, wheat, maize) at subnational scale to (a) look for common features among crop yield dynamics, evaluating their structure and implications for the persistence of that crop; (b) address complex crop responses to changes in environmental growing conditions; and (c) identify climate impact hotspots that are crucial for adaptation and mitigation. We have proposed a novel methodological approach based on dynamics systems in order to understand the processes behind annual crop yield fluctuations. We report the results of general patterns in the internal process (biophysical adjustments by rapid negative feedbacks) regulating crop production and analyse how it influences crop persistence and yield ceilings. The structure of a crop yield dynamic system defines its behaviour, but climate variations could displace it from yield equilibrium and affect its stability. Our findings suggest that weather conditions have a stronger impact on yield growth at high rather than at low yield levels (non‐additive impacts). This allows agriculture management to be refined and applied more efficiently, weakening the relationship between crop productivity and climate change and predicting the response of crop production to yield‐improvement strategies. We have identified those crops and regions which are most vulnerable to the current climate change trends in southern South American agroecosystems. Our results allow us to point to new ways to enhance self‐regulatory success, maximising the efficiency of crop production and reducing climate impacts. We have discussed important implications for crop management and climate change mitigation in an area where agriculture plays a key role in its socioeconomic and ecologic dimensions.     

Untangling ecological complexity on different scales of space and time

Ecological systems are complex and essentially unpredictable, because of the multitude of interactions among their constituents. However, there are general statistical patterns emerging on particular spatial and temporal scales, which indicate the existence of some universal principles behind many ecological phenomena, and which can even be used for the prediction of phenomena occurring on finer scales of resolution. These generalities comprise regular frequency distributions of particular macroscopic variables within higher taxa (body size, abundance, range size), relationships between such variables, and general patterns in species richness. All the patterns are closely related to each other and although there are only a few major explanatory principles, there are plenty of alternative explanations. Reconciliation of different approaches cannot be obtained without careful formulation of testable hypotheses and rigorous quantitative empirical research. Two especially promising ways of untangling ecological complexity comprise: (1) analysis of invariances, i.e. universal quantitative relationships observed within many different systems, and (2) detailed analysis of the anatomy of macroecological phenomena, i.e. explorations of how emergent multispecies patterns are related to regular patterns concerning individual species.

Zusammenfassung

Ökologische Systeme sind komplex und im Wesentlichen aufgrund der Vielzahl von Interaktionen zwischen ihren Bestandteilen nicht vorhersagbar. Dennoch gibt es allgemeine statistische Muster, die in bestimmten räumlichen und zeitlichen Skalen auftreten. Dies weist auf die Existenz von einigen universellen Prinzipien hinter diesen ökologischen Phänomenen hin, die sogar für die Vorhersage von Phänomenen genutzt werden können, die auf kleineren Skalen auftreten. Diese Allgemeingültigkeiten bestehen aus Häufigkeitsverteilungen von bestimmten makroskopischen Variablen innerhalb höherer Taxa (Körpergröße, Abundanz, Arealgröße), den Beziehungen zwischen diesen Variablen und allgemeinen Mustern des Artenreichtums. Alle Muster stehen in enger Beziehung zueinander und obwohl es nur wenige bedeutende Erklärungsprinzipien gibt, existieren viele alternative Erklärungen. Die Abstimmung zwischen verschiedenen Ansätzen kann ohne eine sorgfältige Formulierung von testbaren Hypothesen und rigorose quantitative empirische Forschung nicht erreicht werden. Zwei besonders vielversprechende Wege ökologische Komplexität zu entwirren beinhalten (1) die Analyse von Invarianten, d.h. universellen quantitativen Beziehungen, die innerhalb verschiedener Systeme beobachtet werden, und (2) detaillierte Analysen der Anatomie von makroökologischen Phänomenen, d.h. Untersuchungen darüber, in welcher Beziehung die auftauchenden Muster von Multi-Arten-Systemen zu regulären Mustern individueller Arten stehen.