Otolith size changes related with body growth,habitat depth and temperature

Synopsis Size variation in the sagittal otoliths of six species of the genus Merluccius, and five species of the genus Coelorhynchus was compared, using a digital image processing system and multivariate analysis. It is proposed that otolith growth occurs under dual regulation, overall shape is regulated genetically, and otolith size is influenced by environmental conditions. The decline of temperature with increasing habitat depth seems to be an important factor regulating the growth of otoliths in carbonate-saturated levels. The relative growth of the otoliths is usually negatively allometric.     

Climatic signals in tree rings of <Emphasis Type="Italic">Burkea africana</Emphasis> and <Emphasis Type="Italic">Pterocarpus angolensis</Emphasis> from semiarid forests in Namibia

Tree-ring studies contribute worldwide to the understanding of climate and its relation to tree growth. Long tree-ring chronologies serve as climate proxies for the reconstruction of past, pre-instrument climate and its recent change. In tropical regions, the availability of exactly dated tree-ring chronologies is limited. The dendroclimatic potential of two dominant species from dry forests in northern Namibia was examined in the study presented in this paper. Both species (Burkea africana Hook and Pterocarpus angolensis DC) were sampled at two sites (ca. 900 km apart), and the response to several climatic variables, including ENSO indices, is studied. All specimens showed distinct growth rings and cross-dating between radii was successful for all trees. Species-specific mean curves were built for both sites. The mean curves of different species of the same site synchronised significantly, allowing the construction of a site-specific chronology. Synchronisation between sites was not possible, but spectral analysis of the chronologies implied that both show similar long-term (6.7 year) oscillation patterns. B. africana is more sensitive to rainfall variation than P. angolensis at both sites. Growth response to rainfall was positive, but a time-lag in the reaction occurred between the sites, corresponding to the time-lag of the beginning of the rainy season. Air temperature showed a negative correlation with stem increment at both sites. The response at the westernmost site to two ENSO indices indicates a tree growth decrease during El Niño years, which are generally dry in southern Africa.     

Comparative analysis of glycogen and trehalose accumulation in methylotrophic and nonmethylotrophic yeasts

Trehalose and glycogen accumulate in certain yeast species when they are exposed to unfavorable growth conditions. Accumulations of these reserve carbohydrates in yeasts provide resistance to stress conditions. The results of this study indicate that certain Pichia species do not accumulate high levels of glycogen and trehalose under normal growth conditions. However, depending on the Pichia species, both saccharides accumulate at high levels when the Pichia cells are exposed to unfavorable or stress-inducing growth conditions. Growth in glycerol or methanol medium mostly led to trehalose accumulation in Pichia species tested in this study. It was shown that the metabolic pathways for glycogen and trehalose biosynthesis are present in Pichia species. However, it appears that the biosynthesis of trehalose and glycogen may be regulated in different manners in Pichia species than in the yeast S. cerevisiae. Published in Russian in Mikrobiologiya, 2006, Vol. 75, No. 6, pp. 737–741. The text was submitted by the author in English.     

Growth hormone differentially regulates growth and growth-related gene expression in closely related fish species

Zebrafish (Danio rerio) have become an important model organism for developmental biology and human health studies. We recently demonstrated differential growth patterns between the zebrafish and a close relative the giant danio (Danio aequipinnatus), where the giant danio appears to exhibit indeterminate growth similar to most fish species important for commercial production, while zebrafish exhibit determinate growth more similar to mammalian growth. This study focused on evaluating muscle growth regulation differences in adult zebrafish and giant danio utilizing growth hormone treatment as a mode of growth manipulation. Growth hormone treatment resulted in increased overall growth in giant danio, but failed to increase growth in the zebrafish. Growth hormone treatment increased muscle IGF-I and GHrI gene expression in both species, but to a larger degree in the giant danio. In contrast, zebrafish exhibited a larger increase in IrA and IGF-IrB gene expression in muscle in response to GH treatment. In addition muscle myostatin levels were differentially regulated between the two species, with a down-regulation observed in rapidly growing, GH-treated giant danio and an up-regulation in zebrafish not actively growing in response to GH. This is the first report of differential expression of growth-regulating genes in closely related fish species exhibiting opposing growth paradigms. These results further support the role that the zebrafish and giant danio can play important model organisms for determinate and indeterminate growth.     

Quorum-sensing in Rhizobium

Quorum-sensing signals are found in many species of legume-nodulating rhizobia. In a well-characterized strain of R. leguminosarum biovar viciae, a variety of autoinducers are synthesised, and all have been identified as N-acyl-homoserine lactones. One of these N-acyl-homoserine lactones, is N-(3-hydroxy-7-cis-tetradecenoyl)-L-homoserine lactone, previously known as small bacteriocin, which inhibits the growth of several R. leguminosarum strains. The cinRI locus is responsible for the production of small bacteriocin. CinR induces cinI in response to the AHL made by CinI, thus forming a positive autoregulatory induction loop. A complex cascade of quorum-sensing loops was characterized, in which the cinIR locus appears to be the master control for three other AHL-dependent quorum-sensing control systems. These systems include the raiI/raiR, traI/triR and rhiI/rhiR. Other rhizobial strains appear to share some of these quorum sensing loci, but not all loci are found in all strains. Small bacteriocin along with the other N-acyl-homoserine lactones produced by these three AHL-based control systems regulate (i) growth inhibition of sensitive strains, (ii) transfer of the symbiotic plasmid pRL1JI, and (iii) expression of the rhizosphere-expressed (rhi) genes that influence nodulation. Some of the genes regulated by these systems have been identified. While the functions of some, such as the trb operon regulated by triR are clear, several of the regulated genes have no homologues of known function. It is anticipated that several other genes regulated by these systems have yet to be identified. Therefore, despite the regulation of one of the most complex quorum-sensing cascade being understood, several of the functions regulated by the quorum-sensing genes remain to be elucidated. This revised version was published online in August 2006 with corrections to the Cover Date.     

Inhibition of <Emphasis Type="Italic">Zizania latifolia</Emphasis> growth by <Emphasis Type="Italic">Phragmites australis</Emphasis>: an experimental study

The influence of Phragmites australis on the growth of Zizania latifolia, and the morphological characteristics of both species, were investigated at two nutrient levels. The experiment was carried out over three growing seasons between May 2003 and December 2005. The experimental plot was longitudinally divided into two equal halves, one of which was planted with Zizania latifolia (Zizania zone) and the other one with Phragmites australis (Phragmites zone). Four weeks after transplantation, the plot was again divided horizontally, perpendicular to the previous division, and subject to low (LN) and high nutrient (HN) treatments. Measured growth indices of the two species were more developed in the HN than in the LN treatments. Both species were observed to invade each other’s zone, but Phragmites latifolia seemed to out-compete Zizania latifolia individuals. This was evident from the decrease in below ground biomass of Zizania latifolia in the third growing season and deterioration in above ground organs with time. It was concluded that Phragmites australis out-competes Zizania latifolia due to better developed root and rhizome system.     

The effect of bacteria on interspecific relationships between the euryhaline rotifer Brachionus rotundiformis and the harpacticoid copepod Tigriopus japonicus

Inconsistent results have been obtained on the population growth of Brachionus rotundiformis and Tigriopus japonicus, when results from single-species and two-species mixed cultures are compared. Bacteria growth was not regulated in these experiments, which could be the cause for this. In order to test this possibility, we conducted similar experiments under axenic and synxenic (with presence of one species of bacteria) conditions. The population growth of B. rotundiformis was suppressed by the presence of T. japonicus in axenic cultures. T. japonicus could not persist in axenic cultures, but its population increased when grown in synxenic cultures. T. japonicus used RT bacteria strain as a food source, while these bacteria were toxic to B. rotundiformis. These results suggest that bacteria can modify the interspecific relationship between B. rotundiformis and T. japonicus.     

与物种多样性有关的长白落叶松人工林生物量

对不同龄组长白落叶松(Larix olgensis)人工林群落的物种多样性和生物量及二者关系研究分析。结果表明:1)随林龄增大,群落物种组成结构和多样性特征发生了很大变化。物种更迭现象明显,春榆等阔叶树重要值上升,长白落叶松优势地位逐渐下降,植被类型向针阔混交林演替。群落Sorensen相似性指数降低,Shannon-Winner多样性指数呈"S"型曲线增长,Pielou均匀度指数呈反"S"型曲线下降,Margalef丰富度指数呈单峰曲线增长趋势;2)随林龄增大,群落生物量"S"型曲线增长趋势明显,分配序列为:乔木层木质物残体层灌木层草本层,占群落生物量比例分别为82.41%、15.10%、1.69%和0.81%。长白落叶松生物量占据主导地位,但所占比例持续下降,属于衰退型种群,而春榆等阔叶树比例上升。林下植被层中,草本的主导地位逐渐丧失,灌木取而代之,生物量所占比例明显升高。地表木质物残体生物量比例缓慢下降;3)群落中物种多样性测度指标与生物量之间单调线性增长的关系明显,Shannon多样性指数较之Pielou均匀度指数更适合作群落生物量度量指标,生物量与Margalef丰富度指数无明显相关性。     

<Emphasis Type="Italic">Myrothecium verrucaria</Emphasis> – a potential biological control agent for the invasive ‘old world climbing fern’ (<Emphasis Type="Italic">Lygodium microphyllum</Emphasis>)

One of the greatest threats to the native ecosystems in any part of the world is the invasion and permanent colonization of ecosystems by non-native species. Florida is no exception to this biological invasion, and is currently colonized by an extensive variety of exotic plant species. Originally imported from Asia over 30 years ago, Old World Climbing Fern Lygodium microphyllum (Cavanilles) R. Brown) has become one of the most invasive and destructive weeds in southern Florida. To date different effective control measures of its growth and spread have not been successful; fire and herbicide applications that are currently employed are neither cost effective nor environmentally friendly. In light of the highly delicate ecosystem that is being affected by L. microphyllum, we tested the soil fungus Myrothecium verrucaria (Albertini and Schwein) Ditmar: Fr. for its pathogenicity on the invasive fern. In greenhouse studies the effect of two conidial concentrations of M. verrucaria on L. microphyllum was investigated. Plants were spray inoculated with M. verrucaria which resulted in successful disease development with leaf necrosis symptoms. The higher conidial concentration (1 × 10⁸ ml⁻¹) produced a disease index of approximately 3 on a scale of 0 to 4, day 24 postinitial inoculation, demonstrating the efficacy of this fungus as a severe retardant of Lygodium growth. Preliminary screening of selected native plant species for susceptibility to M. verrucaria showed low disease indices after repeated spray inoculations; the highest index attained was 0.4 by Slash pine (Pinus elliottii).     

玉米KNOX基因家族鉴定及组织和逆境表达分析

为揭示玉米转录因子KNOX家族基因功能,采用生物信息学手段在玉米基因组水平鉴定KNOX家族成员,并对家族基因逆境和组织表达谱进行分析。结果显示:(1)玉米基因组有22个ZmKNOX基因,根据其在染色体上的位置依次命名为ZmKNOX1-ZmKNOX22;编码蛋白质亚细胞定位预测发现,除ZmKNOX5、ZmKNOX11、ZmKNOX12和ZmKNOX15定位于线粒体以及ZmKNOX7定位于细胞质外,其余家族蛋白质均定位于细胞核;进化树分析表明,大多数ZmKNOX与高粱聚在一个分支,表明两物种系统发育关系较近,且基因结构与蛋白进化分类存在一定关联性。(2)全生育期组织表达分析发现,ZmKNOX具有不同的表达模式,且基因的生育期表达模式与蛋白进化分类具有一定相关性。其中ZmKNOX13、ZmKNOX20、ZmKNOX1和ZmKNOX21属全生育期组成型高表达,ZmKNOX3、ZmKNOX5、ZmKNOX6和ZmKNOX14为全生育期组成型低表达,而ZmKNOX4、ZmKNOX8、ZmKNOX9和ZmKNOX17-19的表达具有阶段性和组织特异性,并在胚胎、种子萌发时期、胚芽鞘、茎尖、茎节间、顶端分生组织和花序中较高表达;进一步对生育期数据进行共表达分析发现,ZmKNOX13所在的与根分生发育期相关性最高的模块,与蛋白质泛素化生物学过程密切相关。(3)在盐、冷、热和UV处理下,有8个ZmKNOX家族基因表现出不同的响应模式,但基因表达量变化不大。其中冷处理下ZmKNOX6表达明显上调,热处理下ZmKNOX14明显下调表达,盐胁迫下ZmKNOX13明显上调表达而ZmKNOX13和ZmKNOX14却明显下调,上述3个基因(除ZmKNOX13)均具有生育期低表达的特点。(4)测序数据分析发现,盐处理下叶片中上调的ZmKNOX3和ZmKNOX13基因,根系中下调的ZmKNOX3、ZmKNOX6和ZmKNOX17基因的表达模式基本一致,在不同处理时间ZmKNOX3在叶片和根中均稳定表达,但表达方式相反。研究表明,玉米ZmKNOX家族基因在玉米生长发育和逆境响应过程中具有重要作用。     

不同光照和水分下三叶鬼针草与本地种金盏银盘生长特征的比较研究

为探讨三叶鬼针草(Bidens pilosa)成功入侵机制,利用盆栽试验对不同光照和水分条件下三叶鬼针草与本地种金盏银盘(B.biternata)的生长特征进行了比较研究。结果表明,两物种对光和水的变化均具有较大可塑性,但与金盏银盘相比,在有利环境下三叶鬼针草具有较大的株高、叶面积、生物量;在不利环境下,三叶鬼针草具有较大的比叶面积和叶面积比;除叶面积比和叶生物量比外,三叶鬼针草各生理参数的可塑性指数均高于本地种。这说明三叶鬼针草具有较强的表型可塑性和入侵适应性,这些特性促进了其成功入侵。     

Territory occupancy rate of goshawk and gyrfalcon: no evidence of delayed numerical response to grouse numbers

Two recent studies on territory occupancy rates of goshawk Accipiter gentilis and gyrfalcon Falco rusticolus report a 2–3-year-delayed numerical response to grouse numbers, which is a requirement for a hypothesis of predator-generated grouse cycles. The time lags were assumed to reflect the average age of sexual maturity in the raptor species. In southern Norway, however, subadult (two-year-old) goshawk hens occupied only 18–25% of territories where occupancy was not recorded in the preceding year, and there was no significant relationship between the proportion of subadults among recruits and grouse indices two years earlier. We argue that territory occupancy rates are not appropriate indices of total raptor population levels, but rather reflect the proportion of territorial pairs that attempt to nest. Because this depends on the body condition of the hens, fluctuations in other important winter resident prey species (most important for the goshawk) and winter weather (most important for the gyrfalcon) should also be addressed. During 1988–2006, the annual proportion of goshawk territories with recorded nesting attempts in southern Norway was most closely related to the preceding autumn’s population indices of black grouse Tetrao tetrix and mountain hare Lepus timidus, whereas the annual proportion of gyrfalcon territories with observations of falcons or with confirmed breeding attempts in central Norway were best explained by population indices of willow grouse Lagopus lagopus and ptarmigan L. mutus from the previous autumn, and by December temperatures. Hence, our studies do not support the predation hypothesis for grouse cycles.     

Autotoxicity and chemical defense: nicotine accumulation and carbon gain in solanaceous plants

We quantified the accumulation of and tolerance to exogenously-fed nicotine by monitoring photosynthetic capacity and growth in two nicotine producing species of Solanaceous plants (Nicotiana sylvestris andN. glauca) as well as two Solanaceous species (Datura stramonium andLycopersicon esculentum) that do not produce nicotine to examine the relationship between tolerence and the ability to produce nicotine in defensive quantities. SinceN. sylvestris uses nicotine as an inducible defense, we examined whether nicotine tolerance is induced by damage to examine further the relationship between nicotine tolerence and synthesis. All species were grown in a 1 mM nicotine-containing hydroponic solution. Reductions in the photosynthetic capacity of nicotine-fed plants were found in all species tested. Nicotine-producing species showed no greater tolerance as measured by photosynthetic capacity than the two non-producing species. Leaf damage marginally increased the tolerence ofN. sylvestris to exogeneouslyfed nicotine suggesting that photosynthetic tolerance is coordinated with nicotine production in this nicotine-producing species.N. glauca plants regained photosynthetic capacity after their accumulated nicotine was demethylated to form nornicotine. Leaf nicotine pools in the other three species did not decrease, suggesting that for these species alkaloid metabolism does not play a major role in tolerance. Tolerance, as measured by biomass gained, was higher in the two non-producing species than in the nicotine-producing species suggesting that nicotine may also be functioning as a growth regulator. These results do not support the hypothesis that tolerance is as important as biosynthetic ability in determining which species accumulate defensively significant quantities of nicotine.     

Interactive effects of leaf maturation and phenolics on consumption and growth of a geometrid moth

Phenolic compounds are commonly regarded as the main chemical defenses of deciduous woody plants against insects. To examine how indices of leaf maturation (water content, toughness, and sugar/protein ratio) modified larval consumption and growth relative to phenolics and phenolic-related leaf traits, we measured consumption and growth of fourth-instar Epirrita autumnata (Bkh.) (Lepidoptera: Geometridae) larvae on three different days on young, normal, and mature leaves, respectively, from the same mountain birch (Betula pubescens ssp. czerepanovii (Orlova) Hämet-Ahti) trees. The larvae achieved the same growth rates on young and normal leaves, but had to consume 40% more on the latter. On more mature leaves, larval growth was poorer and was positively correlated with sugar/protein ratios (although the ratio peaked at that time). Indices of leaf maturation correlated with several phenolics in data pooled over the three study days, but poorly in any individual day. Similarly, in the pooled data, larval consumption and growth correlated with several leaf traits, but correlations between leaf and insect traits were few on any of the three days, and no trait was significant on each of the three days.We next examined whether variation in the maturation indices modified the associations of phenolics with insect consumption and growth. When interactions between phenolics and leaf maturation indices were taken into account, the number of phenolic compounds displaying significant associations with insect traits more than doubled. The relative importance of interactive versus direct associations increased with leaf maturation: on young leaves five phenolics showed direct and eleven interactive associations with insect traits, while in mature leaves we found two phenolics to display direct and thirteen phenolics interactive associations. Leaf water content, either alone or together with toughness and sugar/protein ratio, generally explained more of the variance in Epirrita growth (up to 59%) than any phenolic or phenolic-related trait alone (highest value 20%). Including interactive effects between phenolics and indices of leaf maturation in the model increased the proportion explained of variance in larval growth between 49 and 73%. Maturation indices explained 0 to 23% of variance in consumption, and the phenolic compound with the highest (positive!) correlation alone up to 28%, but taking into account interactions between phenolics and maturation indices raised the degree of explanation much (namely, 32 to 53%) over that explained by indices of leaf maturation alone. This indicates strong interactive effects on consumption between phenolics and indices of leaf maturation.     

Habitat characteristics and the effect of various nutrient solutions on growth and mineral nutrition ofArnica montana L. grown on natural soil

Arnica montana, one of the character species of the replacement plant communityViolion caninae on sandy acid humic podzol, is declining in the Netherlands since 1950. Locally, it is even extinct.This process of decline may be attributed to (i) autonomic succession; (ii) increased rate of acidification of the soil and/or (iii) change in competitive relations amongArnica and more productive plant species, such as the successive dominantDeschampsia flexuosa. This paper examines the last two hypothesized factors, supposedly being regulated by atmospheric input of N-input, by (a) describing the habitat characteristics of a seemingly still healthy individual-rich population ofArnica and (b) growingArnica andDeschampsia in mixed humic podzol soil (mainly A₁ horizon) fertilized with variously-composed nutrient solutions in order to assess the nutrient supplying capacity of the podzol soil and species-specific nutritional demands related to their respective growth capabilities.The results suggest that an increased rate of soil acidification yielding extra supply of ionic Al and Mn is presumably of less importance. The implications of growth rate differences amongArnica andDeschampsia as related to their nutritional demands are likely far more important.Arnica grows more slowly thanDeschampsia in fertilized humus podzol. The latter species has a much more efficient use of nutrients. Furthermore, both species differ in K-nutrition if NH₄ ⁺ is the dominant N-source, a situation normally occurring in acid podzolic soils.Deschampsia possesses the capability to adapt its metabolic nutrition (avoiding nutritional imbalances) to a wide range of nutrient supplies thereby maintaining a rather constant level of growth.Arnica, on the contrary, lacks this capability. These results are discussed in the framework of competitive relations among co-occurring plant species in the plant communityViolion caninae. It is concluded that maintenance ofArnica and likely other character species of that alliance — all characterized by a low growth rate — will only be achieved when the plant community is properly managed by trampling, mowing or light levels of grazing (low stocking rate). Of prime importance is to maintain a low and relatively open vegetation structure at a relatively low level of nutrient supply.     

Increase in the production of allelopathic substances by Prymnesium parvum cells grown under N- or P-deficient conditions

The haptophyte Prymnesium parvum is known to produce a set of highly potent exotoxins, commonly called prymnesins. These toxins have been shown to have several biological activities, including ichthyotoxic, neurotoxic, cytotoxic, hepatotoxic and hemolytic activity towards a range of marine organisms. In addition, recent studies have shown that the toxicity of P. parvum is enhanced when the cells are grown under N- or P-deficient conditions. In this study, the influence of prymnesium toxins on the growth of other phytoplankton species was investigated by addition of cell-free filtrate of P. parvum cultures grown under nutrient-deficient (N or P) or non-deficient conditions. Addition of cell-free filtrate from P. parvum cultures grown under N or P limitation inhibited the growth of Thalassiosira weissflogii, Prorocentrum minimum and Rhodomonas cf. baltica. In contrast, a strain of Prymnesium patelliferum known to produce prymnesium toxins was not negatively affected under any conditions. Furthermore, addition of filtrates from nutrient-sufficient P. parvum cultures did not negatively influence the growth of any of the tested species. These findings suggest that prymnesium toxins may play an allelopathic role, and that the production of allelopathic substances is regulated by the availability of nutrients.     

Demography in relation to population density in two herbivorous marsupials: testing for source–sink dynamics versus independent regulation of population size

We compared demography of populations along gradients of population density in two medium-sized herbivorous marsupials, the common brushtail possum Trichosurus vulpecula and the rufous bettong Aepyprymnus rufescens, to test for net dispersal from high density populations (acting as sources) to low density populations (sinks). In both species, population density was positively related to soil fertility, and variation in soil fertility produced large differences in population density of contiguous populations. We predicted that if source–sink dynamics were operating over this density gradient, we should find higher immigration rates in low-density populations, and positive relationships of measures of individual fitness—body condition, reproductive output, juvenile growth rates and survivorship—to population density. This was predicted because under source–sink dynamics, immigration from high-density sites would hold population density above carrying capacity in low-density sites. The study included 13 populations of these two species, representing a more than 50-fold range of density for each species, but we found that individual fitness, immigration rates and population turnover were similar in all populations. We conclude that net dispersal from high to low density populations had little influence on population dynamics in these species; rather, all populations appeared to be independently regulated at carrying capacity, with a balanced exchange of dispersers among populations. These two species have suffered recent reductions in range, and they are ecologically similar to other species that have declined to extinction in inland Australia. It has been argued that part of the cause of the vulnerability of species like these is that they exhibit source–sink dynamics, and disturbance to source habitats can therefore cause large-scale population collapses. The results of our study argue against this interpretation.     

蒙古沙冬青及其伴生植物AM真菌物种多样性

于2015年7月在内蒙古乌海、磴口2个样地选取蒙古沙冬青(Ammopiptanthus mongolicus)及其伴生植物为研究对象,分别采集0-20 cm和20-40 cm土层根围土样,利用高通量测序方法分析了不同植物AM真菌群落结构和物种多样性,发掘新物种,为补充和完善AM真菌分类体系提供依据。试验共分离鉴定3纲5目6科9属89个AM真菌OTU,属包括Glomus,Funneliformis,Diversispora,Claroideoglomus,Rhizophagus,Septoglomus,Scutellospora,Ambispora和Paraglomus。与形态学研究结果相比,高通量鉴定结果在属水平上更丰富。同一土层不同样地,蒙古沙冬青AM真菌丰度和多样性指数高于伴生植物;同一土层不同植物,AM真菌丰度和多样性指数表现为磴口高于乌海;同一植物不同样地,AM真菌ACE指数和Chao1指数20-40 cm土层高于0-20 cm土层,Simpson指数和Shannon指数0-20 cm土层高于20-40 cm土层。RDA分析表明,AM真菌ACE指数和Chao1指数与土壤碱解N显著正相关,与酸性磷酸酶显著负相关;Simpson指数和Shannon指数与碱性磷酸酶显著正相关,与pH显著负相关。结果表明,蒙古沙冬青AM真菌物种多样性高于伴生植物,同一样地,寄主植物与土壤深度共同作用对AM真菌群落组成有显著影响。     

短花针茅荒漠草原α多样性对绵羊载畜率的响应

以短花针茅(Stipa breviflora)荒漠草原为研究对象,采用巢式样方法分析在不同绵羊载畜率下草地的α多样性以及物种组成的变化,探讨荒漠草原生态系统在放牧利用下α多样性对载畜率的响应。结果表明:物种数和α多样性指数随着载畜率的升高而下降。放牧会减少群落非优势物种的相对多度,非优势物种能够反映α多样性。40 m~2为短花针茅荒漠草原多样性研究的最佳取样面积。种-面积关系以及α多样性指数-面积关系符合对数增长模型:y=aln(x)+b。随着取样面积尺度的增加,α多样性指数沿载畜率梯度差异性逐渐增大,在取样面积为0.16 m~2到0.64 m~2时可以体现中、高载畜率和零、低载畜率水平间的差异性,在160 m~2时可以体现各载畜率水平之间的差异显著性。     

Perfect is best: low leaf fluctuating asymmetry reduces herbivory by leaf miners

Fluctuating asymmetry (FA) represents small, random variation from symmetry and can be used as an indicator of plant susceptibility to herbivory. We investigated the effects of FA of two oak species, Quercus laevis and Q. geminata, and the responses of three herbivore guilds: leaf miners, gallers, and chewers. To examine differences in FA and herbivory between individuals, 40 leaves from each tree were collected, and FA indices were calculated. To examine differences in FA and herbivory within-individuals, we sampled pairs of mined and unmined leaves for asymmetry measurements. Differences in growth of leaf miners between leaf types were determined by tracing 50 mines of each species on symmetric leaves and asymmetric leaves. Asymmetric leaves contained significantly lower concentrations of tannins and higher concentrations of nitrogen than symmetric leaves for both plant species. Both frequency of asymmetric leaves on plants and levels of asymmetry positively influenced the abundance of Brachys, Stilbosis and other leaf miners, but no significant relationship between asymmetry and herbivory was observed for Acrocercops. Brachys and Stilbosis mines were smaller on asymmetric leaves, but differences in mine survivorship between symmetric and asymmetric leaves were observed only for Stilbosis mines. This study indicated that leaf miners might use leaf FA as a cue to plant quality, although differential survivorship among leaf types was not observed for all species studied. Reasons for the different results between guilds are discussed.