In this paper,we study the epidemic model of respiratory syncytial virus SIRS with age structure.Firstly,the basic reproduction number R_(0) of the model is calculated and the positivity and ultimate boundedness of th...In this paper,we study the epidemic model of respiratory syncytial virus SIRS with age structure.Firstly,the basic reproduction number R_(0) of the model is calculated and the positivity and ultimate boundedness of the solution to the model under initial conditions are proven.Secondly,it is proven that when R_(0)<1,the disease-free equilibrium is locally and globally asymptotically stable;and when R_(0)>1,the disease is uniformly persistent and there is at least a positive equilibrium.Finally,the effectiveness of the theoretical results is demonstrated by numerical simulation,and the impact of vaccination on disease transmission is predicted.展开更多
Kalimeris integrifolia Turcz. is a root sucker form perennial herb of Compositae. In die late period of growing season, fresh fleshy radicels grow up above the soil surface to develop root-borne buds, which in turn gr...Kalimeris integrifolia Turcz. is a root sucker form perennial herb of Compositae. In die late period of growing season, fresh fleshy radicels grow up above the soil surface to develop root-borne buds, which in turn grow into ramets and taproot. On the basis of observation on numerous samples, methods to classify the age of ramets and buds for the root sucker herbaceous plant population and to estimate the ages of taproots were established according to their morphology. The age of ramets was classified based on the regeneration times of taproot buds. Ramets developed from new root sucker buds were classified as 1 a. After 1 a ramets died, the ramets reproduced from the taproots were 2 a, and so on. New buds from a root sucker were 0 a buds, other age classes of buds were consistent with that of ramets, i.e. buds produced from taproots of I a ramets were 1 a buds, and so on. In the hay clipping meadows of the Songnen Plains, for K. integrifolia population, there are three age classes of ramets, representing a steady age structure. The maximal age of taproots of ramets is 4 a. Among all age classes, the population productivity of 2 a ramets was the highest, and that of I a ramets was the lowest. The ramet productivity increased with ramet age. During the early period of growing season, the productivity of 3 a ramets was the highest, but after the middle of growing season, I a ramets showed the greatest relative growth rate. The population size and age structure in the next year could be accurately forecasted by the number of fresh roots with budlet and present population in late autumn. The potential population in the bud banks was more than two times of the present population, which may provide sufficient substitution in the future.展开更多
The age-structure of natural population of Zoysia japonica in Xiuyan County of Liaoning Province was studied by generational method. The results showed that the highest tiller age class was three, but 1st age class ti...The age-structure of natural population of Zoysia japonica in Xiuyan County of Liaoning Province was studied by generational method. The results showed that the highest tiller age class was three, but 1st age class tillers held dominant posi-tion with proportions over 95% in each month during the growing seasons. The 2nd age class and 3rd age class tillers were minority in the population. So Z. japonica population was an expanding population. The zero age class buds on the rhizomes were dominant in buds age structures. The proportion of buds to tillers on quantity in each month was about 30% to 40% and reached the highest at the end of September. The increasing of buds proportion before dormancy guaranteed the quantity of tillers in the next spring. The biomass of 1st age class tillers changed with time. The biomass kept increasing from April to July and reached the highest at the end of July and then decreased.展开更多
Knowledge of life history is important for understanding possible connections to population declines. Here, we investigated the female age structure and fecundity of Echinotriton chinhaiensis, one of the most endanger...Knowledge of life history is important for understanding possible connections to population declines. Here, we investigated the female age structure and fecundity of Echinotriton chinhaiensis, one of the most endangered salamanders in the world, using skeletochronology based on specimens collected in 2008 and 2009 from a population in Ruiyansi, northeast of Ningbo, Zhejiang, China. The results showed that most female salamanders were between 5 and 6 years of age, with the minimal reproductive age, predicted to be 3 years, and the clutch size correlated to the body size. We argue that both delayed attainment of sexual maturity and low fecundity make this species more vulnerable to extinction.展开更多
The age structure of the natural Zoysia japonica clonal population at QipanMountain in Huishan Scenic Spot of Shenyang, Liaoning Province, China was studied using themorphological method in 2003 and 2004. The dynamics...The age structure of the natural Zoysia japonica clonal population at QipanMountain in Huishan Scenic Spot of Shenyang, Liaoning Province, China was studied using themorphological method in 2003 and 2004. The dynamics of leaves were recorded and the dynamics oftiller and rhizome in the growing season were observed. The results indicated that the rhizomesformed in different years changed in color and rigidity. Its internodes produced in autumn becameshorter. The number of naked nodes changed with the tiller age. Rhizome and tiller characters wereused as a foundation for judging the ages of modules in this study. The longevity of tiller andrhizome was 3 years at most. At the beginning of the growing season, 2-year-old tillers and rhizomespredominated. Then 1-year-old tillers and rhizomes increased rapidly and became dominant in July.The proportion of buds to tillers on quantity was stable at about 30% in the mid-phase of thegrowing season and rose to about 50% in autumn. The seasonal dynamics of tiller, rhizome and bud wasvery important to guarantee the sustained existence of the Zoysia japonica population. The turnoverof modules was the mechanism of sustaining the rejuvenation of the Zoysiajaponica clonalpopulation.展开更多
Age structure of a plant population carries important information on population dynamics. The traditional age classification of individuals by development phases could not explain the generation relationship neither b...Age structure of a plant population carries important information on population dynamics. The traditional age classification of individuals by development phases could not explain the generation relationship neither between individuals nor between modules, and it could not accurately predict the future of population or the tendency of peatland evolution. In a peatland of the Xiao Hinggan Mountains, China, at the middle of the growth season, the age structures of 3 modules, ramets, active buds and rhizomes of a Carex middendorffii clonal population were investigated, with the method of classifying age classes of ramets and active buds by counting generation quantity of tiller nodes, and classifying age classes of rhizomes by their real survival time. The quantity of vegetative ramets was dominant. Tiller nodes of ramets can propagate vegetatively for a maximum of 3 generations. The population of ramets consisted of 3 age classes of ramets at the middle of the growth season, and showed a stable age structure. In the two sampling events, there was no significant difference between quantities and age structure of the population. The maximum age of an excavated rhizome was 12 years old. Rhizomes were classified in 8 age classes, and age classes 4-6 contributed most to the total biomass. There was no significant difference in total length and total biomass per unit area, or in biomass per unit length in rhizomes between the two samplings. Four age classes of active buds were recognized, and their number increased from July to August. The Carex middendorffii clonal population achieved regeneration by budding from the tiller nodes of ramets. The age structures of the 3 modules suggested that the Carex middendorffii clonal population could persist in the early development phase of the oligotrophic peatland in the Xiao Hinggan Mountains, but it could not be dominant. It also faces the risk to disappear from the community as the peatland develops further.展开更多
We used skeletochronology to estimate age structure of the Omei Wood Frog, Rana omeimontis, from southwestern China.Average age differed significantly between males and females.Age at sexual maturity in both males and...We used skeletochronology to estimate age structure of the Omei Wood Frog, Rana omeimontis, from southwestern China.Average age differed significantly between males and females.Age at sexual maturity in both males and females was 1 year. Longevity was 6 and 7 years for males and females, respectively. Average body size differed significantly between the sexes, with females being larger than males. A non-significant correlation between age and body size was found within each sex in this population. The ANCOVA analysis revealed that females also had larger body size than males when the effect of age was controlled.展开更多
Using a theoretical model, this article concludes that age structures influence people＇s propensity to save and thereby influence their capital intensity. In the context that capital and labor are in a substitutional...Using a theoretical model, this article concludes that age structures influence people＇s propensity to save and thereby influence their capital intensity. In the context that capital and labor are in a substitutional relation, increased capital intensity may lead to a drop of labor income share. We perform empirical research with provincial-level data from 1990 to 2007 and have proved that the rising of the old dependency ratio and the decrease of the children dependency rate both contribute to the fall of labor income share. This assumption still holds true after the authors control the influences of other potential factors that may influence labor income share展开更多
Lifespan is one of the main components of life history.Shorter lifespans can be expected in marginal habitats.However,in the case of ectotherms,lifespan typically increases with altitude,even though temperature-one of...Lifespan is one of the main components of life history.Shorter lifespans can be expected in marginal habitats.However,in the case of ectotherms,lifespan typically increases with altitude,even though temperature-one of the main factors to determine ectotherms'life history-declines with elevation.This pattern can be explained by the fact that a shorter activity time favors survival.In this study,we analyzed how lifespan and other life-history traits of the lizard Psammodromus algirus vary along a 2,200 m elevational gradient in Sierra Nevada(SE Spain).Populations at inter-mediate altitudes(1,200-1,700 m),corresponding to the optimal habitat for this species,had the shortest lifespans,whereas populations inhabiting marginal habitats(at both low and at high altitudes)lived longest.Therefore,this lizard did not follow the typical pattern of ectotherms,as it also lived longer at the lower limit of its distribution,nor did it show a longer lifespan in areas with optimal habitats.These results might be explained by a complex combination of different gradients along the mountain,namely that activity time decreases with altitude whereas food availability increases.This could explain why lifespan was maximum at both high(limited activity time)and low(limited food availability)altitudes,resulting in similar lifespans in areas with contrasting environmental conditions.Our findings also indicated that reproductive investment and body condition increase with elevation,suggesting that alpine populations are locally adapted.展开更多
Spatial pattern of trees, basal stem increment and height were examined in a 5.0 ha mixed deciduous/ Pinus koraiensis forest from October in 1984 to May in 1987. Conclusions arc as following: 1. Analysis of the age-st...Spatial pattern of trees, basal stem increment and height were examined in a 5.0 ha mixed deciduous/ Pinus koraiensis forest from October in 1984 to May in 1987. Conclusions arc as following: 1. Analysis of the age-structure of the korcan pine forest shows that it is different from general steady-state forest type. The lack of saplings and individuals in small-diameter class clearly indicates that regeneration is not continuous. Continuous regeneration depends on thinning of the canopy to form a gap. Similar-aged korcan pine seedings grow in these gaps. 2. The horizontal structure of the korcan pine is a mosaic of more or less even-aged groups of trees. The mosaic is a result of korcan pine by regeneration strategy. The aggregations of korcan pine of different ages overlaps to form a continuous population generation. As a results, the population is maintained in steady state.展开更多
Variation in age structure and body size benefits are identified to understand the evolution of life history.Here,we estimated the age structure and body size of two species of odorous frogs(Odorrana margaretae and Od...Variation in age structure and body size benefits are identified to understand the evolution of life history.Here,we estimated the age structure and body size of two species of odorous frogs(Odorrana margaretae and Odorrana grahami)by using skeletochronology.The ages at sexual maturity of O.grahami and O.margaretae in both sexes were 1 and 2 years,respectively.For both sexes,the maximum age observed in O.margaretae was six years.For O.grahami,the maximum age observed in males and females were 4 and 5 years,respectively.Males and females did not differ in mean age in the two species.The average body size of both species considerably differed between sexes,with females being larger than males.The body size of females was also larger than that of males when the effect of age was removed.We also found positive correlations between body size and age within each sex in O.margaretae,but only for female in O.grahami.The female-biased sexual size dimorphism of the two species suggested that fecundity selection for larger female size may increase the reproductive output.展开更多
The effect of genotypic diversity on the age structure and bud bank of the Leymus chinensis population has not yet been demonstrated.This experiment was designed to study the age structure of the tiller,rhizome,and bu...The effect of genotypic diversity on the age structure and bud bank of the Leymus chinensis population has not yet been demonstrated.This experiment was designed to study the age structure of the tiller,rhizome,and bud of L.chinensis at genotypic diversity levels of 1,2,4,8,and 12.A total of 64 communities were established in this experiment,following the principle of randomized block experimental design.The results indicated that genotypic diversity had a significant or obviously significant effect on the cumulative length of rhizomes of 2a and 4a,dry matter accumulation of rhizomes of 1a and 2a,tiller number of 1a,tiller productivity of 3a,but had no significant effect age structure of buds.As the levels of genotypic diversity increased,the proportion of the cumulative length of rhizomes with 4a decreased and then increased,and dry matter accumulation of rhizomes with 1a and 2a gradually increased while the number of tillers with 1a gradually decreased,when the gradient of genotypic diversity increased.At the 1,2,4,8,and 12 genotype diversity levels,the number of tillers,the cumulative length of rhizomes,and dry matter accumulation in rhizomes and buds were all age structures of expanding type.However,tiller productivity was an expanding or stable age structure at levels of 1,2,4,8 genotypic diversity,while it was a declining age structure at the 12 genotype diversity gradient.An appropriate genotypic diversity is conducive to maintaining the growth and stability of the age structure of L.chinensis population,but too high a gradient of genotypic diversity can have a negative impact on the population age structure.This study provided that an appropriate number of genotypic diversity contributes to the stability of the population.展开更多
For a long time, China has large population, so the labor-intensive products become the comparative advantage.This paper analyzes the influences of population age structure＇s changes on the export commodity structure...For a long time, China has large population, so the labor-intensive products become the comparative advantage.This paper analyzes the influences of population age structure＇s changes on the export commodity structure of our country and draws conclusions.展开更多
COVID-19 has triggered an unprecedented public health crisis and a global economic shock.As countries and cities have transitioned away from strict pandemic restrictions,the most effective reopening strategies may var...COVID-19 has triggered an unprecedented public health crisis and a global economic shock.As countries and cities have transitioned away from strict pandemic restrictions,the most effective reopening strategies may vary significantly based on their demographic characteristics and social contact patterns.In this study,we employed an extended agespecific compartment model that incorporates population mobility to investigate the interaction between population age structure and various containment interventions in New York,Los Angeles,Daegu,and Nairobi e four cities with distinct age distributions that served as local epicenters of the epidemic from January 2020 to March 2021.Our results demonstrated that individual social distancing or quarantine strategies alone cannot effectively curb the spread of infection over a one-year period.However,a combined strategy,including school closure,50%working from home,50%reduction in other mobility,10%quarantine rate,and city lockdown interventions,can effectively suppress the infection.Furthermore,our findings revealed that social-distancing policies exhibit strong age-specific effects,and age-targeted interventions can yield significant spillover benefits.Specifically,reducing contact rates among the population under 20 can prevent 14%,18%,56%,and 99%of infections across all age groups in New York,Los Angeles,Daegu,and Nairobi,respectively,surpassing the effectiveness of policies exclusively targeting adults over 60 years old.In particular,to protect the elderly,it is essential to reduce contacts between the younger population and people of all age groups,especially those over 60 years old.While an older population structure may escalate fatality risk,it might also decrease infection risk.Moreover,a higher basic reproduction number amplifies the impact of an older population structure on the fatality risk of the elderly.The considerable variations in susceptibility,severity,and mobility across age groups underscore the need for targeted interventions to effectively control the spread of COVID-19 and mitigate risks in future pandemics.展开更多
This paper is concerned with the sustained periodic oscillation phenomenon in a threespecies delayed predation system with Holling type II functional response and age structure in top predator.The top predator fertili...This paper is concerned with the sustained periodic oscillation phenomenon in a threespecies delayed predation system with Holling type II functional response and age structure in top predator.The top predator fertility function is regarded as a piecewise continuous smooth function with regard to their maturation period T2.The complicated dynamic behavior is proved by integrated semigroup theory and Hopf bifurcation theorem for semilinear equations with non-dense domain.Through qualitative analysis and bifurcation study of the system,we yield that this system has a nontrivial periodic solution that bifurcates from the positive equilibrium age distribution when bifurcation parameter T passes through some critical values.Numerical simulations are also provided to illustrate theoretically analytical results.展开更多
This paper was based on data collected during the 38th and 39th Chinese National Antarctic Research Expeditions in the Amundsen Sea. The spatiotemporal distribution patterns of length(total length, AT) and sexual matu...This paper was based on data collected during the 38th and 39th Chinese National Antarctic Research Expeditions in the Amundsen Sea. The spatiotemporal distribution patterns of length(total length, AT) and sexual maturity stages of Antarctic krill(Euphausia superba) were examined. The age structure and geographic distribution of cluster groups also were studied. The results reveal significant diurnal variations in the length and maturity stages of Antarctic krill during the morning(MRN) to morning twilight(MTW) period, with mean lengths ranging from 28.92 to 45.87 mm. Two cyclical patterns were observed.Regarding maturity stages, the krill were composed of juveniles, adult males, and adult females in increasing order of proportion,with a notably higher proportion of non-gravid females compared to gravid females, and mainly distributed in evening twilight(ETW) to dawn(DWN), MTW to day(DAY), MRN to MTW, MRN to MTW and night(NIT) to DAY periods, respectively.Significant spatial variations in krill length and maturity stages occur, with a marked regional boundary around 130°W. K-means clustering analysis of krill length identified Group Ⅰ, Group Ⅱ, and Group Ⅲ, with dominant age classes of 3+, 0 and 3+, and 3+to 4+, respectively. Group Ⅱ was widely distributed in the surveyed waters, whereas Group Ⅰ and Group Ⅲ were distributed only in waters west of 130°W. The study area features a significant continental slope, where adults and gravid females were primarily distributed on its slopes and to the south. This spatial pattern also profoundly influenced the distribution of different cluster groups.展开更多
Aims Neutral theory consists of a suite of models that assume ecological equivalence among individual organisms.They have been most commonly applied to tropical forest tree communities either as null models or as appr...Aims Neutral theory consists of a suite of models that assume ecological equivalence among individual organisms.They have been most commonly applied to tropical forest tree communities either as null models or as approximations.Neutral models typically only include reproductive adults;therefore,fitting to empirical tree community data requires defining a reproductive-size threshold,which for trees is usually set arbitrarily to a diameter at breast height(DBH)of 100 mm.The inevitable exclusion of some reproductive adults and inclusion of some saplings cause a non-random sampling bias in neutral model fits.Here,we investigate this problem and resolve it by introducing simple age structure into a neutral model.Methods We compared the performance and sensitivity of DBH threshold of three variants of a spatially explicit neutral model:the traditional model,a model incorporating random sampling and a model with two distinct age classes—reproductive adults and saplings.In the age-structured model,saplings are offspring from adults that disperse according to a Gaussian dispersal kernel around the adults.The only extra parameter is the ratio of adults to saplings,which is not a free parameter but directly measurable.We used species–area relationships(SARs)to explore the predicted effect of saplings on the species richness at different scales in our model.We then evaluated the three model variations to find the parameters required to maintain the observed level of species richness in the 50-ha plot on Barro Colorado Island(BCI).We repeated our analysis filtering the data at different minimum tree-size thresholds in order to find the effect this threshold has on our results.Lastly,we used empirical species–individual relationships(SIRs)to test the pre-existing hypothesis that environmental filtering is the primary cause of differences between the assemblage of saplings and that of adults on BCI.Important Findings Our age-structured neutral model was characterized by SARs that were insensitive to the presence of saplings at large scales and highly sensitive to them at small scales.Both models without age structure were highly sensitive to the DBH threshold chosen in a way that could not be explained based on random samplings alone.The age-structured neutral model,which allowed for non-random sampling based on life stage,was consistent with species richness observations.Our analysis of empirical SIRs did not support environmental filtering as a dominant force,but it did show evidence for other differences between age classes.Age can now be easily incorporated into future studies of neutral models whenever there is a concern that a sample is not entirely composed of reproductive adult individuals.More generally,we suggest that modeling studies using tree data subject to a minimum size threshold should consider the sensitivity of their results to that threshold.展开更多
Objective:More similar locations may have similar infectious disease dynamics.There is clear overlap in putative causes for epidemic similarity,such as geographic distance,age structure,and population size.We compare ...Objective:More similar locations may have similar infectious disease dynamics.There is clear overlap in putative causes for epidemic similarity,such as geographic distance,age structure,and population size.We compare the effects of these potential drivers on epidemic similarity compared to a baseline assumption that differences in the basic reproductive number(R0)will translate to differences in epidemic trajectories.Methods:Using COVID-19 case counts from United States counties,we explore the importance of geographic distance,population size differences,and age structure dissimilarity on resulting epidemic similarity.Results:We find clear effects of geographic space,age structure,population size,and R0 on epidemic similarity,but notably the effect of age structure was stronger than the baseline assumption that differences in R0 would be most related to epidemic similarity.Conclusions:Together,this highlights the role of spatial and demographic processes on SARS-CoV2 epidemics in the United States.展开更多
Pseudorabies is a highly contagious disease caused by pseudorabies virus(PRV)or suid herpesvirus 1(SuHV1),causing significant economic losses to the swine industry in countries where the disease exists.In this paper,w...Pseudorabies is a highly contagious disease caused by pseudorabies virus(PRV)or suid herpesvirus 1(SuHV1),causing significant economic losses to the swine industry in countries where the disease exists.In this paper,we formulate an age structure model of pseudorabies virus that takes into account disease-related mortality and vertical trans-mission.We find a threshold to determine the stability and existence of the disease.We show that there is always a globally asymptotically stable boundary equilibrium if and only if R_(02)<1+q,which means that the disease always exists in piglets and will die out in adult pigs.When R_(02)>1+q,the boundary equilibrium is unstable and there exists a unique disease-endemic equilibrium,which is globally asymptotically stable.We give detailed proofs of our theoretical results and numerical examples.Brief concluding re-marks are also provided.展开更多
基金supported by the Natural Science Foundation of Xinjiang(No.2022D01E41)the National Natural Science Foundation of China(No.12261087)the Open Project of Key Laboratory of Applied Mathematics of Xinjiang Autonomous Region(No.2021D04014)。
文摘In this paper,we study the epidemic model of respiratory syncytial virus SIRS with age structure.Firstly,the basic reproduction number R_(0) of the model is calculated and the positivity and ultimate boundedness of the solution to the model under initial conditions are proven.Secondly,it is proven that when R_(0)<1,the disease-free equilibrium is locally and globally asymptotically stable;and when R_(0)>1,the disease is uniformly persistent and there is at least a positive equilibrium.Finally,the effectiveness of the theoretical results is demonstrated by numerical simulation,and the impact of vaccination on disease transmission is predicted.
文摘Kalimeris integrifolia Turcz. is a root sucker form perennial herb of Compositae. In die late period of growing season, fresh fleshy radicels grow up above the soil surface to develop root-borne buds, which in turn grow into ramets and taproot. On the basis of observation on numerous samples, methods to classify the age of ramets and buds for the root sucker herbaceous plant population and to estimate the ages of taproots were established according to their morphology. The age of ramets was classified based on the regeneration times of taproot buds. Ramets developed from new root sucker buds were classified as 1 a. After 1 a ramets died, the ramets reproduced from the taproots were 2 a, and so on. New buds from a root sucker were 0 a buds, other age classes of buds were consistent with that of ramets, i.e. buds produced from taproots of I a ramets were 1 a buds, and so on. In the hay clipping meadows of the Songnen Plains, for K. integrifolia population, there are three age classes of ramets, representing a steady age structure. The maximal age of taproots of ramets is 4 a. Among all age classes, the population productivity of 2 a ramets was the highest, and that of I a ramets was the lowest. The ramet productivity increased with ramet age. During the early period of growing season, the productivity of 3 a ramets was the highest, but after the middle of growing season, I a ramets showed the greatest relative growth rate. The population size and age structure in the next year could be accurately forecasted by the number of fresh roots with budlet and present population in late autumn. The potential population in the bud banks was more than two times of the present population, which may provide sufficient substitution in the future.
基金This study was supported by the NKBRSF (G1999043407-1) Knowledge Innovation Program of the Chinese Academy of Sciences (KZCX2-406+3 种基金 SCXZD0101) NKTRDP (2001BA510B-07 2002BA516A20) and Education Committee Projects of Liaong Province (990121400
文摘The age-structure of natural population of Zoysia japonica in Xiuyan County of Liaoning Province was studied by generational method. The results showed that the highest tiller age class was three, but 1st age class tillers held dominant posi-tion with proportions over 95% in each month during the growing seasons. The 2nd age class and 3rd age class tillers were minority in the population. So Z. japonica population was an expanding population. The zero age class buds on the rhizomes were dominant in buds age structures. The proportion of buds to tillers on quantity in each month was about 30% to 40% and reached the highest at the end of September. The increasing of buds proportion before dormancy guaranteed the quantity of tillers in the next spring. The biomass of 1st age class tillers changed with time. The biomass kept increasing from April to July and reached the highest at the end of July and then decreased.
基金supported by the National Natu-ral Science Foundation of China(30770316)
文摘Knowledge of life history is important for understanding possible connections to population declines. Here, we investigated the female age structure and fecundity of Echinotriton chinhaiensis, one of the most endangered salamanders in the world, using skeletochronology based on specimens collected in 2008 and 2009 from a population in Ruiyansi, northeast of Ningbo, Zhejiang, China. The results showed that most female salamanders were between 5 and 6 years of age, with the minimal reproductive age, predicted to be 3 years, and the clutch size correlated to the body size. We argue that both delayed attainment of sexual maturity and low fecundity make this species more vulnerable to extinction.
基金This study was supported by Doctor Startup Foundation of Liaoning Province (20031029), Doctor Startup Foundation of Shenyang Normal University and Director Foundation of Shenyang Normal University (sy200513).
文摘The age structure of the natural Zoysia japonica clonal population at QipanMountain in Huishan Scenic Spot of Shenyang, Liaoning Province, China was studied using themorphological method in 2003 and 2004. The dynamics of leaves were recorded and the dynamics oftiller and rhizome in the growing season were observed. The results indicated that the rhizomesformed in different years changed in color and rigidity. Its internodes produced in autumn becameshorter. The number of naked nodes changed with the tiller age. Rhizome and tiller characters wereused as a foundation for judging the ages of modules in this study. The longevity of tiller andrhizome was 3 years at most. At the beginning of the growing season, 2-year-old tillers and rhizomespredominated. Then 1-year-old tillers and rhizomes increased rapidly and became dominant in July.The proportion of buds to tillers on quantity was stable at about 30% in the mid-phase of thegrowing season and rose to about 50% in autumn. The seasonal dynamics of tiller, rhizome and bud wasvery important to guarantee the sustained existence of the Zoysia japonica population. The turnoverof modules was the mechanism of sustaining the rejuvenation of the Zoysiajaponica clonalpopulation.
文摘Age structure of a plant population carries important information on population dynamics. The traditional age classification of individuals by development phases could not explain the generation relationship neither between individuals nor between modules, and it could not accurately predict the future of population or the tendency of peatland evolution. In a peatland of the Xiao Hinggan Mountains, China, at the middle of the growth season, the age structures of 3 modules, ramets, active buds and rhizomes of a Carex middendorffii clonal population were investigated, with the method of classifying age classes of ramets and active buds by counting generation quantity of tiller nodes, and classifying age classes of rhizomes by their real survival time. The quantity of vegetative ramets was dominant. Tiller nodes of ramets can propagate vegetatively for a maximum of 3 generations. The population of ramets consisted of 3 age classes of ramets at the middle of the growth season, and showed a stable age structure. In the two sampling events, there was no significant difference between quantities and age structure of the population. The maximum age of an excavated rhizome was 12 years old. Rhizomes were classified in 8 age classes, and age classes 4-6 contributed most to the total biomass. There was no significant difference in total length and total biomass per unit area, or in biomass per unit length in rhizomes between the two samplings. Four age classes of active buds were recognized, and their number increased from July to August. The Carex middendorffii clonal population achieved regeneration by budding from the tiller nodes of ramets. The age structures of the 3 modules suggested that the Carex middendorffii clonal population could persist in the early development phase of the oligotrophic peatland in the Xiao Hinggan Mountains, but it could not be dominant. It also faces the risk to disappear from the community as the peatland develops further.
基金Financial support was provided by the National Natural Science Foundation of China (31101633)the Foundation of Key Laboratory of Southwest China Wildlife Resources Conservation (Ministry of Education)+1 种基金China West Normal UniversityChina (XNYB01-3).
文摘We used skeletochronology to estimate age structure of the Omei Wood Frog, Rana omeimontis, from southwestern China.Average age differed significantly between males and females.Age at sexual maturity in both males and females was 1 year. Longevity was 6 and 7 years for males and females, respectively. Average body size differed significantly between the sexes, with females being larger than males. A non-significant correlation between age and body size was found within each sex in this population. The ANCOVA analysis revealed that females also had larger body size than males when the effect of age was controlled.
文摘Using a theoretical model, this article concludes that age structures influence people＇s propensity to save and thereby influence their capital intensity. In the context that capital and labor are in a substitutional relation, increased capital intensity may lead to a drop of labor income share. We perform empirical research with provincial-level data from 1990 to 2007 and have proved that the rising of the old dependency ratio and the decrease of the children dependency rate both contribute to the fall of labor income share. This assumption still holds true after the authors control the influences of other potential factors that may influence labor income share
基金the Ministerio de Ciencia e Innovacion(project CG L2009-13185)M.C.was supported by the Ministerio de Economia y Competencia,through the Scvcro Ochoa Programme for Centres of Excellence in R+D-I-I[SEV-2012-0262]with the contract SVP-2014-068620.F.J.Z.C.(ref:AP2009-3505)and S.R.(ref:AP2009-1325)were supported through 2 predoctoral grants(FPU programme)from the Ministerio de Educacion(Ministry of Education).
文摘Lifespan is one of the main components of life history.Shorter lifespans can be expected in marginal habitats.However,in the case of ectotherms,lifespan typically increases with altitude,even though temperature-one of the main factors to determine ectotherms'life history-declines with elevation.This pattern can be explained by the fact that a shorter activity time favors survival.In this study,we analyzed how lifespan and other life-history traits of the lizard Psammodromus algirus vary along a 2,200 m elevational gradient in Sierra Nevada(SE Spain).Populations at inter-mediate altitudes(1,200-1,700 m),corresponding to the optimal habitat for this species,had the shortest lifespans,whereas populations inhabiting marginal habitats(at both low and at high altitudes)lived longest.Therefore,this lizard did not follow the typical pattern of ectotherms,as it also lived longer at the lower limit of its distribution,nor did it show a longer lifespan in areas with optimal habitats.These results might be explained by a complex combination of different gradients along the mountain,namely that activity time decreases with altitude whereas food availability increases.This could explain why lifespan was maximum at both high(limited activity time)and low(limited food availability)altitudes,resulting in similar lifespans in areas with contrasting environmental conditions.Our findings also indicated that reproductive investment and body condition increase with elevation,suggesting that alpine populations are locally adapted.
文摘Spatial pattern of trees, basal stem increment and height were examined in a 5.0 ha mixed deciduous/ Pinus koraiensis forest from October in 1984 to May in 1987. Conclusions arc as following: 1. Analysis of the age-structure of the korcan pine forest shows that it is different from general steady-state forest type. The lack of saplings and individuals in small-diameter class clearly indicates that regeneration is not continuous. Continuous regeneration depends on thinning of the canopy to form a gap. Similar-aged korcan pine seedings grow in these gaps. 2. The horizontal structure of the korcan pine is a mosaic of more or less even-aged groups of trees. The mosaic is a result of korcan pine by regeneration strategy. The aggregations of korcan pine of different ages overlaps to form a continuous population generation. As a results, the population is maintained in steady state.
基金Financial support was provided by the National Natural Sciences Foundation of China(Nos.31772451,31970393)the Science and Technology Youth Innovation Team of Sichuan Province(2019JDTD0012)。
文摘Variation in age structure and body size benefits are identified to understand the evolution of life history.Here,we estimated the age structure and body size of two species of odorous frogs(Odorrana margaretae and Odorrana grahami)by using skeletochronology.The ages at sexual maturity of O.grahami and O.margaretae in both sexes were 1 and 2 years,respectively.For both sexes,the maximum age observed in O.margaretae was six years.For O.grahami,the maximum age observed in males and females were 4 and 5 years,respectively.Males and females did not differ in mean age in the two species.The average body size of both species considerably differed between sexes,with females being larger than males.The body size of females was also larger than that of males when the effect of age was removed.We also found positive correlations between body size and age within each sex in O.margaretae,but only for female in O.grahami.The female-biased sexual size dimorphism of the two species suggested that fecundity selection for larger female size may increase the reproductive output.
基金supported by the National Natural Science Foundation of China(32071860).
文摘The effect of genotypic diversity on the age structure and bud bank of the Leymus chinensis population has not yet been demonstrated.This experiment was designed to study the age structure of the tiller,rhizome,and bud of L.chinensis at genotypic diversity levels of 1,2,4,8,and 12.A total of 64 communities were established in this experiment,following the principle of randomized block experimental design.The results indicated that genotypic diversity had a significant or obviously significant effect on the cumulative length of rhizomes of 2a and 4a,dry matter accumulation of rhizomes of 1a and 2a,tiller number of 1a,tiller productivity of 3a,but had no significant effect age structure of buds.As the levels of genotypic diversity increased,the proportion of the cumulative length of rhizomes with 4a decreased and then increased,and dry matter accumulation of rhizomes with 1a and 2a gradually increased while the number of tillers with 1a gradually decreased,when the gradient of genotypic diversity increased.At the 1,2,4,8,and 12 genotype diversity levels,the number of tillers,the cumulative length of rhizomes,and dry matter accumulation in rhizomes and buds were all age structures of expanding type.However,tiller productivity was an expanding or stable age structure at levels of 1,2,4,8 genotypic diversity,while it was a declining age structure at the 12 genotype diversity gradient.An appropriate genotypic diversity is conducive to maintaining the growth and stability of the age structure of L.chinensis population,but too high a gradient of genotypic diversity can have a negative impact on the population age structure.This study provided that an appropriate number of genotypic diversity contributes to the stability of the population.
文摘For a long time, China has large population, so the labor-intensive products become the comparative advantage.This paper analyzes the influences of population age structure＇s changes on the export commodity structure of our country and draws conclusions.
基金funding from the National Natural Science Foundation of China(grant 71904104)the China Postdoctoral Science Foundation(grant 2019M650726)+1 种基金funding from Qiushi Foundation,the Resnick Sustainability Institute at California Institute of Technology and the National Natural Science Foundation of China(grant 71874097 and 41921005)DMK gratefully acknowledges the support of the Zaffaroni Family Foundation,the Karsten Family Foundation,and US NSF CyberSEES Grant 1539585 and NSF InFEWS grant DGE 1633740.
文摘COVID-19 has triggered an unprecedented public health crisis and a global economic shock.As countries and cities have transitioned away from strict pandemic restrictions,the most effective reopening strategies may vary significantly based on their demographic characteristics and social contact patterns.In this study,we employed an extended agespecific compartment model that incorporates population mobility to investigate the interaction between population age structure and various containment interventions in New York,Los Angeles,Daegu,and Nairobi e four cities with distinct age distributions that served as local epicenters of the epidemic from January 2020 to March 2021.Our results demonstrated that individual social distancing or quarantine strategies alone cannot effectively curb the spread of infection over a one-year period.However,a combined strategy,including school closure,50%working from home,50%reduction in other mobility,10%quarantine rate,and city lockdown interventions,can effectively suppress the infection.Furthermore,our findings revealed that social-distancing policies exhibit strong age-specific effects,and age-targeted interventions can yield significant spillover benefits.Specifically,reducing contact rates among the population under 20 can prevent 14%,18%,56%,and 99%of infections across all age groups in New York,Los Angeles,Daegu,and Nairobi,respectively,surpassing the effectiveness of policies exclusively targeting adults over 60 years old.In particular,to protect the elderly,it is essential to reduce contacts between the younger population and people of all age groups,especially those over 60 years old.While an older population structure may escalate fatality risk,it might also decrease infection risk.Moreover,a higher basic reproduction number amplifies the impact of an older population structure on the fatality risk of the elderly.The considerable variations in susceptibility,severity,and mobility across age groups underscore the need for targeted interventions to effectively control the spread of COVID-19 and mitigate risks in future pandemics.
文摘This paper is concerned with the sustained periodic oscillation phenomenon in a threespecies delayed predation system with Holling type II functional response and age structure in top predator.The top predator fertility function is regarded as a piecewise continuous smooth function with regard to their maturation period T2.The complicated dynamic behavior is proved by integrated semigroup theory and Hopf bifurcation theorem for semilinear equations with non-dense domain.Through qualitative analysis and bifurcation study of the system,we yield that this system has a nontrivial periodic solution that bifurcates from the positive equilibrium age distribution when bifurcation parameter T passes through some critical values.Numerical simulations are also provided to illustrate theoretically analytical results.
基金supported by the 38th and 39th CHINAREs and all members of the two Antarctic cruisessupported by Ministry of Natural Resources of the People’s Republic of China and the Chinese Arctic and Antarctic Administration。
文摘This paper was based on data collected during the 38th and 39th Chinese National Antarctic Research Expeditions in the Amundsen Sea. The spatiotemporal distribution patterns of length(total length, AT) and sexual maturity stages of Antarctic krill(Euphausia superba) were examined. The age structure and geographic distribution of cluster groups also were studied. The results reveal significant diurnal variations in the length and maturity stages of Antarctic krill during the morning(MRN) to morning twilight(MTW) period, with mean lengths ranging from 28.92 to 45.87 mm. Two cyclical patterns were observed.Regarding maturity stages, the krill were composed of juveniles, adult males, and adult females in increasing order of proportion,with a notably higher proportion of non-gravid females compared to gravid females, and mainly distributed in evening twilight(ETW) to dawn(DWN), MTW to day(DAY), MRN to MTW, MRN to MTW and night(NIT) to DAY periods, respectively.Significant spatial variations in krill length and maturity stages occur, with a marked regional boundary around 130°W. K-means clustering analysis of krill length identified Group Ⅰ, Group Ⅱ, and Group Ⅲ, with dominant age classes of 3+, 0 and 3+, and 3+to 4+, respectively. Group Ⅱ was widely distributed in the surveyed waters, whereas Group Ⅰ and Group Ⅲ were distributed only in waters west of 130°W. The study area features a significant continental slope, where adults and gravid females were primarily distributed on its slopes and to the south. This spatial pattern also profoundly influenced the distribution of different cluster groups.
基金Engineering and Physical Sciences Research Council overseas postdoctoral research fellowship at the life sciences interface(EP/F043112/1 to J.R.)the Netherlands Organization for Scientific Research(NWO-ALW 864-07-007 to R.S.E.,NWOALW 863-07-008 to P.A.J.).
文摘Aims Neutral theory consists of a suite of models that assume ecological equivalence among individual organisms.They have been most commonly applied to tropical forest tree communities either as null models or as approximations.Neutral models typically only include reproductive adults;therefore,fitting to empirical tree community data requires defining a reproductive-size threshold,which for trees is usually set arbitrarily to a diameter at breast height(DBH)of 100 mm.The inevitable exclusion of some reproductive adults and inclusion of some saplings cause a non-random sampling bias in neutral model fits.Here,we investigate this problem and resolve it by introducing simple age structure into a neutral model.Methods We compared the performance and sensitivity of DBH threshold of three variants of a spatially explicit neutral model:the traditional model,a model incorporating random sampling and a model with two distinct age classes—reproductive adults and saplings.In the age-structured model,saplings are offspring from adults that disperse according to a Gaussian dispersal kernel around the adults.The only extra parameter is the ratio of adults to saplings,which is not a free parameter but directly measurable.We used species–area relationships(SARs)to explore the predicted effect of saplings on the species richness at different scales in our model.We then evaluated the three model variations to find the parameters required to maintain the observed level of species richness in the 50-ha plot on Barro Colorado Island(BCI).We repeated our analysis filtering the data at different minimum tree-size thresholds in order to find the effect this threshold has on our results.Lastly,we used empirical species–individual relationships(SIRs)to test the pre-existing hypothesis that environmental filtering is the primary cause of differences between the assemblage of saplings and that of adults on BCI.Important Findings Our age-structured neutral model was characterized by SARs that were insensitive to the presence of saplings at large scales and highly sensitive to them at small scales.Both models without age structure were highly sensitive to the DBH threshold chosen in a way that could not be explained based on random samplings alone.The age-structured neutral model,which allowed for non-random sampling based on life stage,was consistent with species richness observations.Our analysis of empirical SIRs did not support environmental filtering as a dominant force,but it did show evidence for other differences between age classes.Age can now be easily incorporated into future studies of neutral models whenever there is a concern that a sample is not entirely composed of reproductive adult individuals.More generally,we suggest that modeling studies using tree data subject to a minimum size threshold should consider the sensitivity of their results to that threshold.
基金supported by the U.S.National Science Foundation RAPID grant(NSF-DEB-2031196).
文摘Objective:More similar locations may have similar infectious disease dynamics.There is clear overlap in putative causes for epidemic similarity,such as geographic distance,age structure,and population size.We compare the effects of these potential drivers on epidemic similarity compared to a baseline assumption that differences in the basic reproductive number(R0)will translate to differences in epidemic trajectories.Methods:Using COVID-19 case counts from United States counties,we explore the importance of geographic distance,population size differences,and age structure dissimilarity on resulting epidemic similarity.Results:We find clear effects of geographic space,age structure,population size,and R0 on epidemic similarity,but notably the effect of age structure was stronger than the baseline assumption that differences in R0 would be most related to epidemic similarity.Conclusions:Together,this highlights the role of spatial and demographic processes on SARS-CoV2 epidemics in the United States.
基金supported by National Natural Science Foundation of China(12071095,11971127).
文摘Pseudorabies is a highly contagious disease caused by pseudorabies virus(PRV)or suid herpesvirus 1(SuHV1),causing significant economic losses to the swine industry in countries where the disease exists.In this paper,we formulate an age structure model of pseudorabies virus that takes into account disease-related mortality and vertical trans-mission.We find a threshold to determine the stability and existence of the disease.We show that there is always a globally asymptotically stable boundary equilibrium if and only if R_(02)<1+q,which means that the disease always exists in piglets and will die out in adult pigs.When R_(02)>1+q,the boundary equilibrium is unstable and there exists a unique disease-endemic equilibrium,which is globally asymptotically stable.We give detailed proofs of our theoretical results and numerical examples.Brief concluding re-marks are also provided.
