Evaluation and analysis of intraspecific competition in maize: A case study on plant density experiment

Intraspecific competition is a common phenomenon in agricultural production,and maize is one of the most sensitive grass species to intraspecific competition due to its low tillering ability.This study evaluated and analyzed intraspecific competition in maize,and screened competitive indices that could be used to evaluate intraspecific competition in a maize population.A 2-year field experiment was conducted using the maize hybrid Zhongdan 2 at 12 plant densities ranging from 1.5 to 18.0 plants（pl）m-2.The results showed that the response of single-plant grain yield and dry matter at harvest to increased plant density decreased exponentially and that the harvest index decreased linearly.The response of population-level grain yield to plant density was curvilinear,producing a maximum value at the optimum population density.However,the yielddensity equation agreed well with the Steinhart-Hart equation curves,but not with the quadratic equation curves reported by most previous studies.Competitive indices are used to evaluate competition in a plant population or plant species.The present results show that competitive intensity（CI）and absolute severity of competition（ASC）increased with increasing plant density;however,relative yield（RY）and relative reproductive efficiency（RReff）decreased.The different responses of these indices reflect different aspects of competition.According to the analysis of CI,ASC,RY,and RReff,higher CI and ASC values indicate higher intraspecific competition,whereas higher RY and RReff values indirectly reflect lower intraspecific competition.These competitive indices evaluate not only the intraspecific competitive intensity under different plant densities of the same cultivar but also those of different cultivars under the same plant density.However,some overlap exists in the calculations of ASC,CI,and RY,so one could simply select any one of these indices to evaluate intraspecific competition in a maize population.In conclusion,the present study provides a method to evaluate intraspecific competition in maize populations,which may be beneficial for breeding high-yield maize varieties in the future.

INTRASPECIFIC CROSSINGS OF UNDARIA PINNATIFIDA (HARV.) SUR.-A POSSIBLE TIME-SAVING WAY OF STRAIN SELECTION

Unicellular gametophytes of Undaria pinnatifida (Harv.) Sur. were isolated in Qingdao, P. R. China in April 1993 and in Tokushima, southem Japan in March 1995. Diferent intraspecific crossings by using unicellular male and female gametophytes were successfully undertaken in Sept. of 1995 in Qingdao.Sporophytes were transplanted to two different locations for open an cultivation. One was at Zhanqiao (ZQ) Bay where the water current was slower than that of another location - Taipingjiao(TPJ). A total of218 adult sporophytes were harvested on January 12 and 18 from TPJ and ZQ repectively. For eacncombination, 10 sporophytes un cultivated. Analysis of the mprpholgical characteristics of adult spprophytes indicated that the longest length between two bases of the serration of pinnate bldes (W2) is a morphological characteristic that can be transferred from the parent plant to the next generations regardless of environmental variations. There was evidence that W2 was apparently determined by sex-linked factors, i.e, by male parental grametophyte.. Sporophytes from certain crossing combinations showed more vigorous growth than those from other crossing combinations. It is therrfore possible to select grametophyte strains which can be used as parental gametophytes for the seeding production of sporophytes with more vigorous growth within shorter cultivation period. The morphology of hybrids from a Qingdao strain and a Tokushima cultivated strain resembled that of both parental plants in frond feaures (wrinkled or smooth) and W2. Sporophyll formation also varied with strains. The fact that adult sporophytes resulting from the same crossing combinations have identical morphological characteristics under the same environmental conditions indicates the possibility of a new way to select strains which are expected to be ideal for commerical production by purposely selecting, propagating, and seeding unicellular gametophytes for sporeing production through freeliving techniques of gametophytes.

Potential tradeoffs between intraspecific and interspecific trait variations along an environmental gradient in a subtropical forest

There has been growing attention to intraspecific variation in trait-based plant ecology. However, studies on these changes across ontogenetic stages and the potential trade-offs with interspecific traits along environmental gradients are rare. In this study, we measured six wood and bark traits of 1030 trees of six species(Castanopsis nigrescens; C. carlesii; Lithocarpus polystachyus; L. synbalanos; Ormosia glaberrima; O. pachycarpa) from a10-ha plot in a subtropical forest. Mean intraspecific variation in bark thickness and bark percentage to DBH was more than twice that for wood density and bark density.Bark thickness and bark percentage showed a consistent trend with increasing tree size. Small-tree traits were more variable than the same traits in larger trees. Altitude,convexity and soil nutrients explained the majority of the variations in the six traits, while sibling species had similar relationships between traits and environmental variables.Trees with dense wood and thin bark were usually found on steep slopes at lower altitudes. Our findings show intraspecific trait variability has different spatial patterns compared with interspecific variabilities along an environmental gradient.

Identifying Intraspecific Variation in Venom Yield of Chinese Cobra(Naja atra) from Ten Populations in China's Mainland

Detailed information on venom yield is helpful in preparing antivenoms and treating snakebites, but such information is lacking for many species of venomous snakes. The Chinese cobra(Naja atra) is a large sized, venomous snake commonly found in southeastern China, where it causes a heavy burden of snakebites. To examine the effects of various factors(morphology, sex, age, season, and geographical origin) on the venom yield in this snake, we collected venom samples of 446 individuals(426 adults and 20 neonates) from 10 populations of N. atra over an eightyear period. We used two variables, lyophilized venom mass(venom yield) and solid content of venom(% solids), to quantify the venom yield. We used linear regression analysis to check if venom yield was related to morphological factors, one-way ANOVA and one-way ANCOVA to detect the sexual, ontogenetic, and geographic variation in venom yield, and repeated-measures ANOVA to examine seasonal shifts in venom yield. Our results indicate that venom yield of N. atra is positively related to the morphological traits examined, with male snakes expelling more venom than females. Venom yield in N. atra was age-related, with elder snakes always expelling more venom than younger ones. Geographic variation in venom yield was also observed, while seasonal variation was not. The solid content of venom was lower in males than in females, but this was not related to morphology, season, age, or geography. Our findings suggest that venom yield in N. atra is influenced by multiple factors, as well as by the interactions among these factors.

Intraspecific diversity: adaptive differentiation of Picea mongolica W. D. Xu ecotypes

Picea mongolica W. D. Xu is an endemic and endangered species which is only found in semi-arid areas of northern China. It has been widely used as an afforestation tree in the establishment of the Three-North Shelterbelt System for its adaptation to arid soils and as a virescent tree in urban gardens and streets for its beautiful shape. Due to different microenvironments, P. mongolica populations may differentiate into many ecological groups with different adaptive abilities. Long-term adaptation to a dry environment makes P. mongolica differentiate into different ecotypes. Typical ecotypes are P. mongolica f. purpurea （Fp）, P. mongolica f. rubra （Fr） and P. mongolica f. viridis （Fv）. Our results show that cone size is clearly not uniform among different ecotypes; the largest cones are found in the Fv ecotype and the smallest in Fp. There were also distinct differences between these ecotypes in terms of height and length of squama. At the molecular level, the zymograms of peroxidase and lipase prove the existence of different ecotypes in P. mongolica. The results are useful for investigating and managing this rare spruce species in China.

Strong intraspecific trait variation in a tropical dominant tree species along an elevational gradient

Functional trait variation of plant species includes both inter-and intraspecific variation;however,traitbased plant ecology generally considers only interspecific variation while ignoring intraspecific variation.One reason for this neglect is that intraspecific variation may be negligible when compared to interspecific variation;however,direct comparisons between inter-and intraspecific variation of plant species are lacking,especially in tropical forests.Here we investigated intraspecific leaf trait variation(leaf area,specific leaf area,leaf thickness,leaf density,leaf chlorophyll content) of Pittosporopsis kerrii Craib(Icacinaceae),the most abundant tree species in the Xishuangbanna tropical seasonal rainforest in southwestern China,along an elevational gradient(703-824 m).We found a substantial range of intraspecific variation in P.kerrii that was never less than 22.1% of range of the interspecific variation among 462 tree species reported before in the same community.Moreover,with increased elevation,both leaf thickness and density increased and specific leaf area decreased significantly.It could be more important for the individuals of P.kerrii to produce thicker and denser leaves to tolerate environmental stress(e.g,soil water availability) rather than having high growth rates at the places with higher elevation in the Xishuangbanna tropical seasonal rainforest.

Intraspecific leaf morphological variation in Quercus dentata Thunb.:a comparison of traditional and geometric morphometric methods,a pilot study

To compare the application of traditional morphometric methods(TMMs)and geometric morphometric methods(GMMs)in the study of intraspecific leaf morphological characters of Quercus dentata,fifteen linear measurement indices and thirteen landmarks of leaves were used to study leaf morphology of three provenances(H1,H2,and H3).In TMMs,principal component analysis(PCA)showed that leaf size–related indices played an important role in population classification.Partial least square(PLS)analysis showed that the main morphological characters affecting leaf size were the average depth of the lobes and the length–width ratios.However,the important indices to distinguish the provenances were circularity,leaf width,and length–width ratio.The results of discriminant analysis(DA)showed that 74.0%of H1,68.0%of H2,and 74.0%of H3 were correctly classified.Cluster analysis showed that the Mahalanobis distances between H1 and H2,H1 and H3,and H2 and H3 were 4.3761,11.4629,and 10.2067,respectively.In GMMs,PCA based on symmetrical components showed that the difference in leaf morphology was mainly due to the changing trend of the leaf apex and base,petiole length,and degree of leaf cracking.PLS analysis showed that there was a significant covariation between the leaf symmetrical components and size:as the leaf enlarged,the widest part gradually moved up,and the shape changed from nearly oval to lanceolate.DA results showed that 86.0%and 78.0%of H1 and H2,70.0%and 80.0%of H1 and H3,and 82.0%and 76.0%of H2 and H3 were correctly classified.Canonical variate analysis results showed that the Mahalanobis distances between H1 and H2,H1 and H3,and H2 and H3 were 1.7238,1.5380,and 1.6329,respectively.Both GMMs and TMMs showed significant differences in morphology among the three Q.dentata provenances,but GMMs had higher classification accuracy and could provide more information about leaf shape,whereas TMMs could provide more information about leaf size.Based on our results,GMMs are promising in the study of leaf morphological variation within Q.dentata provenances.

Intraspecific morphometric diversity of barramundi (Lates calcariferBloch, 1790) in the waters of southern Bangladesh

A total of 160 barramundi's (Lates calcarifer Bloch, 1790) sampled from four rivers (Tentulia, Balaswar, Bakkhali, and Andarmanik) along the southern coastal region of Bangladesh were investigated in terms of morphometric characters to reveal the intraspecific variation. Twenty-five morphometric measurements were extracted using the conventional method and subjected to multivariate analyses (i.e., principal component analysis (PCA), discriminate function analysis (DFA), cluster analysis (CA)) to distinguish individuals from different rivers. The result demonstrated that twenty-two out of 25 measurements was statistically significant (Univariate ANOVA) among all four populations. PCA analysis of morphometric characters resulted in two principal components, PC I and PCⅡ which accounted for 79.25% and 4.28% of the total data variance. PC I-PC Ⅱ plot explained 83.53% of total variance differentiated the population of L. calcarifer into two groups. Discriminate analysis correctly classified about 88.1% of the examined fish into the four areas. The UPGMA dendrogram showed that Bakkhali populations were the most morphologically different populations in comparison to other populations, while Andarmanik and Balaswar populations were very close to each other. The strong morphometric variation between Bakkhali and Tentulia, Andarmanik and Balaswar was observed in the present study, suggested the evidence of the separate stock population of barramundi in these locations, which might require distinct stock management strategies for resource sustainability in the waters of southern Bangladesh. However, if these findings are supported by further molecular markers and geometric morphometry, this would be a strong indication of different stocks of this population in the four rivers of southern Bangladesh.

Cell number explains the intraspecific spur-length variation in an Aquilegia species

Variations of nectar spur length allow pollinators to utilize resources in novel ways,leading to the different selective pressures on spurs and allowing taxa to diversify.However,the mechanisms underlying spur length variation remain unclear.Interspecific comparisons of spur length suggest that both cell division and anisotropic expansion could explain the changes of spur length,and that hormone-related genes contribute to the process of spur formation.In contrast,little is known about intraspecific spur length variation.In Aquilegia rockii,spur length varies strikingly,ranging from 1 mm to 18 mm.To examine the potential mechanisms underlying spur length variation in A.rockii,we observed cell morphology and analyzed RNA-seq of short-and long-spurred flowers.Scanning electron microscopy revealed that at two positions on spurs there were no differences in either cell density or cell anisotropy between short-and long-spurred flowers,suggesting that in A.rockii changes in cell number may explain variations in spur length.In addition,we screened transcriptomes of short-and long-spurred flowers for differentially expressed genes;this screen identified several genes linked to cell division(e.g.,F-box,CDKB2-2,and LST8),a finding which is consistent with our analysis of the cellular morphology of spurs.However,we did not find any highly expressed genes involved in the hormone pathway in long-spurred flowers.In contrast to previous hypotheses that anisotropic cell expansion leads to interspecific spur variation in Aquilegia,our results suggest that cell number changes and related genes are mainly responsible for spur length variations of A.rockii.Furthermore,the underlying mechanisms of similar floral traits in morphology may be quite different,enriching our understanding of the mechanisms of flower diversity in angiosperms.

On the intraspecific variability in basal metabolism and the food habits hypothesis in birds

The food habits hypothesis (FHH) stands as one of the most striking and often-cited interspecific patterns to emergefrom comparative studies of endothermic energetics. The FHH identifies three components of diet that potentially produce variabilityin mass-independent BMR, i.e. food quality, food availability, and food predictability or environmental productivity. Thehypothesis predicts that species with diets of low energy content and/or low digestibility should evolve low mass-independentBMRs. The effects of food habits on BMR have been widely investigated at the interspecific level, but the variation between individualsand populations has been largely ignored. Our focus is to compare predictions derived from interspecific studies withdata collected from within-species studies to explore the mechanisms and functional significance of adaptive responses predictedby the food-habits hypothesis among birds. We conclude that if BMR is correlated with daily energy expenditure, then organismsthat can lower BMR will reduce daily energy expenditure and hence, food requirements. Birds that lower BMR in stressful environmentsmay increase survival. Nevertheless, the mechanism (s) by which birds eating a low quality diet reduce BMR andwhether lower BMR affects fitness remain to be

Intraspecific Variability and Problematic Dimorphism in the Early Cretaceous(Valanginian)Ammonite Saynoceras verrucosum(d'Orbigny,1841)

The population of Saynoceras verrucosum （d＇Orbigny） from the Polish basin （Wawal section, central Poland） shows no significant intraspecific variability. Dimorphism has not been found in this population. Statistical analyses of material from the shallow epicratonic Polish basin and the relatively deep Vocontian basin （southeastern France） indicated two populations. Forms from the Polish basin are somewhat more inflated and smaller than forms from the Vocontian basin.

Intraspecific Phylogenetic Relationships of Caryopteris incana in the Tsushima Islands, Japan, Using DNA Sequence Analysis

Caryopteris incana is a perennial shrub distributed in the temperate zone of the East Asia. It is found in West Kyushu in Japan, where it is designated as an endangered species. Tsushima, Nagasaki, which experienced repeated connection and fragmentation between the Korean Peninsula and Japan, is an island on the route along which C. incana moved to Japan from continental Asia. We conducted field work and confirmed the genetic structure of populations using DNA sequence analysis to construct a detailed distribution map and clarify the intraspecific phylogenetic relationships of C. incana in Tsushima Island. We confirmed 72 populations in Tsushima. Using the leaves of individuals cultivated from seeds collected from each natural population, we analyzed the chloroplast and nuclear DNA sequence variations. Among the populations, sequence variations were confirmed in six regions of chloroplast DNA, and six haplotypes, including base substitutions, were distinguished. Two haplotypes were mainly divided at the border of the northern part of the southern island in Tsushima. One population in the northwestern part of the north island showed a haplotype derived from the southern part. This finding revealed that the distribution of C. incana had been artificially influenced. Several haplotypes were confirmed by sequence variations in the northern populations, but only one haplotype in the southern populations, suggesting that C. incana on the north island had separated early from the south island in Tsushima.

Intraspecific Relationship of Sheep Based on Mitochondrial Cytochrome b Gene

[ Objective] To preliminarily explore the intraspecific relationship of sheep based on cytochrome b （ Cyt b） gene of mitochondrial DNA （mtDNA）. [Method] The Cyt b gene sequences in 112 sheep individuals of two local sheep breeds were amplified by PCR. Then the amplified products were digested with EcoR I and analyzed by restriction fragment length polymorphism （RFLP）. [ Result] As many as 56 samples from Tan sheep and 56 samples from Wadi sheep were detected. The results showed that the amplified Cyt b gene in 51 individuals of Tan sheep had one EcoR I restriction site and no EcoR I restriction site in other five individuals, thus the Cyt b gene in Tan sheep showed two restriction morphs; the Cyt b gene in all 56 individuals of Wadi sheep had one EcoR I restriction site and showed one restriction morph. [ Conclusion] The polymorphism of mitochondrial Cyt b gene in Tan sheep and Wadi sheep is poor, and the Cyt b gene in sheep breeds is very conservative. Therefore, using Cyt b gene as gene marker to study the intraspecific relationship of sheep has some limitations.

Evolutionary history of a desert perennial Arnebia szechenyi(Boraginaceae):Intraspecific divergence,regional expansion and asymmetric gene flow

The complex interactions of historical,geological and climatic events on plant evolution have been an important research focus for many years.However,the role of desert formation and expansion in shaping the genetic structures and demographic histories of plants occurring in arid areas has not been well explored.In the present study,we investigated the phylogeography of Arnebia szechenyi,a desert herb showing a near-circular distribution surrounding the Tengger Desert in Northwest China.We measured genetic diversity of populations using three maternally inherited chloroplast DNA(cpDNA)fragments and seven bi-paternally inherited nuclear DNA(nDNA)loci that were sequenced from individuals collected from 16 natural populations across its range and modelled current and historical potential habitats of the species.Our data indicated a considerably high level of genetic variation within A.szechenyi and noteworthy asymmetry in historical migration from the east to the west.Moreover,two nuclear genetic groups of populations were revealed,corresponding to the two geographic regions separated by the Tengger Desert.However,analysis of cpDNA data did not show significant geographic structure.The most plausible explanation for the discrepancy between our findings based on cpDNA and nDNA data is that A.szechenyi populations experienced long periods of geographic isolation followed by range expansion,which would have promoted generalized recombination of the nuclear genome.Our findings further highlight the important role that the Tengger Desert,together with the Helan Mountains,has played in the evolution of desert plants and the preservation of biodiversity in arid Northwest China.

Role of intraspecific competition in intrinsic growth rate regulation in an Oikopleura dioica(Tunicata)population

Planktonic Oikopleura dioica respond almost instantly to opportunistic algal blooms,but it is unknown whether the population increase can change from an exponential to a logistic model to avoid a final sudden collapse.To test the hypothesis that intraspecific competition regulates the intrinsic rate of natural increase(r),density-dependent effects on growth and reproduction performance were investigated in O.dioica via laboratory incubations.Over a large food concentration range,batch maturation was observed above the per capita food supply(PFS)of 8.1µgC/ind.in 4.5 d.Somatic growth was saturated beyond this PFS value,whereas gonad length increased continuously.Below this threshold,individuals reached small body and gonad lengths,and maturation was rarely observed during the incubation period.The gonad/body volume and maturation ratios also increased with the PFS.Instead of the food concentration,the r values were regulated by competition pressure via variability in maturation duration and the proportion of mature individuals in the cohorts.When the minimum food demand was satisfied in the designated generation time,the r value tended to be regulated by the spawning proportion in the population.Otherwise,prolonged development duration and decreased r values were expected.

Intraspecific trait variation of woody species reduced in a savanna community,southwest China

Plants deploy various ecological strategies in response to environmental heterogeneity.In many forest ecosystems,plants have been reported to have notable inter-and intra-specific trait variation,as well as clear phylogenetic signals,indicating that these species possess a degree of phenotypic plasticity to cope with habitat variation in the community.Savanna communities,however,grow in an open canopy structure and exhibit little species diversification,likely as a result of strong environmental stress.In this study,we hypothesized that the phylogenetic signals of savanna species would be weak,the intraspecific trait variation(ITV)would be low,and the contribution of intraspecific variation to total trait variance would be reduced,owing to low species richness,multiple stresses and relatively homogenous community structure.To test these hypotheses,we sampled dominant woody species in a dry-hot savanna in southwestern China,focusing on leaf traits related to adaptability of plants to harsh conditions(yearround intense radiation,low soil fertility and seasonal droughts).We found weak phylogenetic signals in leaf traits and low ITV(at both individual and canopy-layer levels).Intraspecific variation(including leaf-,layer-and individual-scales)contributed little to the total trait variance,whereas interspecific variation and variation in leaf phenology explained substantial variance.Our study suggests that intraspecific trait variation is reduced in savanna community.Furthermore,our findings indicate that classifying species by leaf phenology may help better understand how species coexist under similar habitats with strong stresses.

草地贪夜蛾与甜菜夜蛾种内和种间的竞争行为

草地贪夜蛾Spodoptera frugiperda(Smith)和甜菜夜蛾Spodoptera exigua(Hübner)是我国重要的农作物害虫,存在很多共同的寄主植物。为明确草地贪夜蛾和甜菜夜蛾的竞争关系,本文在食物充足和食物缺乏条件下,研究了草地贪夜蛾和甜菜夜蛾种内和种间竞争行为;研究了不同初始种群密度草地贪夜蛾和甜菜夜蛾初孵幼虫在相同生态位的种群竞争行为。结果表明:无食物条件下,扭动行为是草地贪夜蛾种内竞争最主要的行为表现,其中3龄与5龄幼虫组合扭动行为出现次数最多,为8.57±0.49次/30 min。与无食物处理相比,有食物处理下草地贪夜蛾攻防行为次数较少。种间竞争中,在无食物条件下二者攻击行为主要表现为头部接触,防御主要表现为扭动行为,其中草地贪夜蛾4龄幼虫与甜菜夜蛾5龄幼虫竞争时头部接触和扭动行为最频繁,分别出现5.03±2.43次/30 min和18.47±5.92次/30 min。此外,同一龄期的草地贪夜蛾和甜菜夜蛾种间竞争中,草地贪夜蛾存活率更高;不同龄期两者竞争时,龄期相对较高的幼虫存活率更高,且有食物时两者存活率均高于无食物处理。种群竞争的室内模拟研究中,草地贪夜蛾和甜菜夜蛾种群的存活率随共存时间的增加逐渐降低。重复测量方差分析表明,5头草地贪夜蛾幼虫与40头甜菜夜蛾幼虫接入玉米苗后,共存时间没有显著影响草地贪夜蛾幼虫的存活率,但甜菜夜蛾幼虫的存活率受共存时间影响显著;其他组合中共存时间均显著影响草地贪夜蛾与甜菜夜蛾幼虫的存活率,其中,40头草地贪夜蛾幼虫与40头甜菜夜蛾幼虫接入玉米苗后,两者存活率均存在显著差异,草地贪夜蛾的存活率显著高于甜菜夜蛾,草地贪夜蛾种群可能取代甜菜夜蛾种群。研究结果可为明确草地贪夜蛾和甜菜夜蛾的种群演替规律及制定科学的防治措施提供参考。

广西十万大山山地常绿阔叶林优势种空间分布格局与关联性

【目的】山地常绿阔叶林是十万大山的主要植被类型,揭示其群落种群空间分布格局与关联性特征,有利于探讨群落物种竞争关系与维持机制。【方法】以十万大山1 hm^(2)山地常绿阔叶林样地重要值排名前6位的树种为研究对象,采用g(r)函数、方差比率法、Spearman秩相关系数分析种群空间分布格局和种内、种间相关性。【结果】以完全随机模型对样地群落优势种空间分布格局进行分析,发现优势种在1~11 m尺度上均呈聚集分布,云南桤叶树Clethra delavayi、银木荷Schima argentea、柔毛紫茎Stewartia villosa在1~25 m尺度上呈聚集分布;以异质泊松模型分析时,发现优势种在10~25 m尺度上均呈随机分布,表明优势种空间分布格局受生境异质性影响,且不同种群受影响的程度不同;样地微地形因子中海拔和坡度对优势种的格局分布影响较大;不同种群的龄级空间分布格局受个体密度影响较大,增长型种群幼龄个体聚集分布,随着龄级的增加其空间分布趋于随机分布,衰退型种群成年个体小尺度上聚集分布,幼龄个体随机分布;样地群落优势种的幼树、小树、成年树之间无种内竞争排斥关系,种内关联性均为正相关或无关联,种内关联性与尺度相关;群落优势种种间关联性总体呈正关联,种间正相关和无关联种对多于负相关种对,表明群落中优势种的种间竞争关系较弱,优势种间相互独立,利于物种共存。【结论】十万大山山地常绿阔叶林优势种的分布格局受生境异质性和密度制约的影响,且分布格局随尺度和发育阶段而变化。种内、种间关系多为正相关或无关联,群落优势种排斥竞争关系不显著,群落种群结构稳定。

基于激光雷达数据的塔里木河下游胡杨种群空间分布格局和种内竞争关系

【目的】分析胡杨种群在干旱区不同地下水埋深梯度下的空间分布格局及种内竞争强度变化,探究种群空间结构对干旱环境的响应特征。【方法】在塔里木河下游3个断面处离河道1 000 m的范围内等距离布设15个50 m×50 m天然胡杨林样地,利用地面激光雷达(TLS)获取树木三维结构数据,并通过聚集指数(R)、丛生指数(I)、点格局函数g(r)等空间分布指标以及竞争指数(CI),分析空间分布格局和种内竞争强度。【结果】1)R和I指数表明,在下游不同地下水埋深梯度下,胡杨种群空间分布格局整体上呈聚集分布。2)各样地内在0~25 m半径r距离获取的g(r)函数值分析表明,大部分样地胡杨在r<5 m距离内基本呈现聚集分布格局,在r>5 m距离呈随机分布格局。随着地下水埋深增加,树木聚集分布的距离r会缩小。3)点格局函数g_(12)(r)结果表明,不同龄级胡杨树分布格局存在差异,中龄树主要呈聚集分布,其他龄级树呈随机分布;中龄树与幼龄树、成熟树之间存在正关联性,表现出相互促进关系,而其他龄级树木之间未呈现显著关联性。4)平均CI指数随离河道距离增大呈递减趋势,单木CI随胸径增大逐渐递减。【结论】塔里木河下游胡杨种群在小尺度上呈聚集分布格局,随着尺度的增加主要呈现随机分布特征。随离河道距离增大和地下水位逐步降低,导致树木密度降低和种内平均竞争强度变弱,树木呈衰退趋势。

草地贪夜蛾卵寄生蜂——夜蛾黑卵蜂的种内识别及过寄生

夜蛾黑卵蜂是重大入侵害虫草地贪夜蛾的重要卵期寄生蜂。为明确夜蛾黑卵蜂的种内识别及过寄生现象,测定了夜蛾黑卵蜂对被同种自体(同一个体)或异体(不同个体)雌蜂寄生不同时间间隔后的寄主卵的识别能力,并研究了单头和多头雌蜂在不同寄主密度下的过寄生率。结果发现,无论自体或异体寄生识别,夜蛾黑卵蜂的过寄生率均为0。单头雌蜂在不同蜂卵比下寄生24 h后,寄主卵内寄生蜂1龄幼虫的百分比均小于100%,且每粒寄主卵内只有1头1龄幼虫。多头雌蜂在寄主数量充足条件下,当蜂卵比为1:100、2:200、4:400、6:600、8:800时,未被寄生的寄主卵的百分比分别为52.8%、67.2%、63.2%、53.6%和51.2%,含1头寄生蜂1龄幼虫的寄主卵的百分比分别为47.2%、32.8%、36.8%、46.4%和48.8%;多头雌蜂在寄主数量不足条件下,当蜂卵比为2:20、3:21、4:20、7:21、20:20时,夜蛾黑卵蜂的寄生率分别为60.0%、83.0%、95.0%、94.0%和96.0%,过寄生率分别为11.0%、38.0%、64.0%、73.0%和92.0%;单粒寄主卵内寄生蜂1龄幼虫的平均数量分别为0.4、0.6、1.1、1.3和2.1头,最大数量分别为3.0、4.0、5.0、6.0和12.0头。结果表明,夜蛾黑卵蜂具有自体和异体寄生识别能力;单头雌蜂的过寄生率与寄主数量无关;多头雌蜂在寄主数量充足的条件下,不会产生过寄生;但在寄主数量不足的条件下,随着蜂卵比升高,寄生率、过寄生率、单粒草地贪夜蛾卵内寄生蜂1龄幼虫的平均数和最大数均随之增加。蜂卵比为4:20时寄生率高,过寄生率低,内部竞争低,是较为合适的接蜂比例。