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At least 19 recordsLinked to original sources
PubMed1986

Reproduction rate and viability of Merino, Nilagiri and halfbred Merino. II. Age specific replacement rate and net reproduction rate.

Age specific replacement rate, net reproduction rate and intrinsic rate of population increase were estimated from records over a period of 11 years of Merino, Nilagiri and halfbreds. On an average for every 1000 ewes mated 830 ewes lambed, 917 lambs were born, 898 lambs were weaned and 422 ewe lambs survived to joining age (one and a half years) in Nilagiri sheep. The corresponding figures were 665, 685, 590 and 228 in Merino and 664, 709, 691 and 341 in halfbreds. Nilagiri ewes in intermediate ages had more multiple births and older ewes weaned more lambs. The flock strength was not maintained unless the ewes were kept till the fifth lambing in Merino, third lambing in Nilagiri and fourth lambing in halfbred Merino. These results along with the culling levels indicated that the low reproductive efficiency in halfbreds may not be critical enough to avoid introduction of Merino for improvement in productivity. However, the poor reproductive efficiency of the Merino in this country may necessitate repeat importations of Merino rams for production of halfbreds.

Age Factors↗
PubMed1994

A reconstruction of the population of north Italy from 1650 to 1881 using annual inverse projection with comparisons to England, France, and Sweden.

"North Italy annual population and vital rates are reconstructed from 1650 to 1881 using series of vital event indices from many rural parishes and cities. Inverse projection is applied to the reconstructed series of vital events and population to generate annual age distribution, gross reproduction rate, net reproduction rate, life expectancy at birth, and infant mortality rate. The results are compared with official sources and detailed demographic rates produced by annual inverse projection using data from England, France, and Sweden. Over the long term, North Italy is generally characterized by stagnant and relatively high mortality. Fertility and nuptiality are relatively high at the beginning and at the end of the period." (SUMMARY IN FRE)

Demography↗
PubMed1983

Generalization of the immigration and the stable population model.

Building upon an idea presented by Espenshade, Bouvier and Arthur (1982) about the eventual stationarity of a population subjected to a net reproduction rate of less than one and a constant stream of immigration, this note reports the consequences upon the birth trajectory for all possible values of the net reproduction rate. It has been shown that when the net reproduction rate is equal to one, the number of births increases linearly with time. As may be expected, the increase is exponential for values of net reproduction rate greater than one.

Emigration and Immigration↗
PubMedDate not supplied

[Vital statistics of Rhodnius neivai Lent, 1953 (Hemiptera: Reduviidae) under experimental conditions].

A statistical evaluation of the population dynamics of R. neivai is based on six cohorts experiments conducted under controlled laboratory conditions. Two blood sources were offered to animals: rabbit and hen. Egg hatching, nymphal development time and mortality, adult longevity and age-specific mortality, female age-specific fecundity and fertility were determined. In addition, some population parameters were evaluated, such as: life expectancy, intrinsic rate of natural increase, net reproduction rate, finite rate of increase, reproductive value and stable age distribution. Life cycle was longer in the animals fed on rabbit, nymphal survival was slightly higher in the individuals fed on hen. Age of first reproduction was lower in the insects fed on hen, but reproductive output and total number of reproductive weeks were greater in the cohorts fed on rabbit. Intrinsic and finite rate of increase were greater in the animals fed on hen. Generation time was slightly greater in the cohorts fed on rabbit. Net reproduction rate was similar on both blood sources, although it was slightly bigger in the individuals fed on rabbit. Reproductive value in the insects fed on rabbit was twice as much as the registered in the animals fed on hen.

Actuarial Analysis↗
PubMed1965

On the mathematical analysis of schistosome populations.

The concept of the stationary ecological life-table has been applied to populations of the three main species of schistosomes affecting man. In such a system, the net reproductive rate should be equal to 1.0, with reproduction and mortality balancing each other. Calculations are made of net reproduction in both snail and mammal hosts and of the probabilities of transmission from each host to the other. By far the most complete data are those for Schistosoma japonicum, for which the net reproductive rate is calculated as 0.588. The error probably represents the inadequacy of information on rat populations. Using much less complete data, the net reproductive rate for S. mansoni is calculated as 1.85 and for S. haematobium as 2.74. The relative departure from the expected value of 1.0 thus reflects the lack of complete information on the respective parasites. Details of the method and examples of each kind of calculation are given.It is estimated that with adequate data from three or four areas with a range of transmission rates, a predictive model could be constructed for the epidemiology of one species of parasite, and that adequate staff could obtain the necessary data in two-and-a-half years.

Animals↗
PubMed2000

Social enhancement of fitness in yellow-bellied marmots.

The yellow-bellied marmot (Marmota flaviventris) is a social, ground-dwelling squirrel that lives either individually or in kin groups of from two to five adult females. Philopatry and daughter recruitment lead to the formation and persistence of matrilines at habitat sites. By using 37 years of demographic data for 12 habitat sites, we could determine long-term trends in the effects of group size on two measures of fitness, survivorship and net reproductive rate, which otherwise are obscured by annual fluctuations in these measures. Both size and number of matrilines varied among sites and survivorship and net reproductive rate varied among sites and among matriline sizes. The role of social organization was explored further by examining the effect of matriline size, averaged over all years and sites, on fitness. For both survivorship and net reproductive rate the relationship with matriline size was curvilinear. Fitness increased with the increase in matriline size and then decreased in the largest groups. Decreased fitness in matrilines of four or five was associated with agonistic behavior, a large number of 2-year-old females in the social group, and reproductive suppression. There is no evidence that females acted to increase their fitness by increasing indirect fitness; i.e., by assisting relatives, but attempted to increase direct fitness. Direct fitness increased when mortality and fission of large matrilines reduced group size and the surviving females increased reproduction.

Animals↗
PubMed1985

[Tempo and parity structure of Japanese fertility].

The present study is part of a larger project on the formal demographic analysis of Japanese fertility. It deals with the most elusive aspect of fertility, that is the tempo of fertility. The temporal aspect of fertility, particularly in terms of cohort fertility framework with speical reference to parity of women, has been emphasized by Whelpton and Ryder, but in the Japanese demography there have scarcely been studies of this aspect, probably due to lack of interest. In very recent years, however, interest has grown, reflecting the need for more accurate fertility projections in the future in connection with population projections. The present study is an application of life table techniques to explore the temporal aspect of fertility in Japan. 2 methods have been used. One is the age-marriage-parity specific net reproduction rate tables, which were first constructed by the senior author of this paper. The other is by Professor Chin Long Chiang at the University of California, Berkely. In the application of the former type, net reproduction rate tables were constructed for 3 dates -- 1970-71, 1975-76, and 1980-81. Through this method, it was demonstrated that recent fertility for the period 1980-81 was reduced, partly because of the decline in fertility in live-birth order of 1 and 2 among the relatively young ages up to 25 years old. On the other hand, for the ages up to 30 years old, some catching-up mechanisms took place. The 2nd method is by Chiang's new approach to the fertility table. According to his method, which was included in his new book entitled Life Tables and Its Applications, parity-oriented fertility tables have been constructed for the Japanese females for every year from 1971 through 1983, both inclusive. In these cases, denominator is for year z while numerator is concerned with yea z + 1. This method is particularly interesting since it can calculate waiting time for childbearing until the completion of family formation. Some of the findings indicated: 1) recent increases in both parity progession ratio and parity-specific fertility rate in low parity augur a future increase in fertility in the period measure in the near future; and 2) a shortening of the waiting time until the completion of family formation around 1981 and then the recovery of its lengthening in the years 1982 and 1983 suggest a recent trend of lengthening actual reproductive period which definitely contributes to an increase in fertility.

Asia↗
PubMed1989

Growth rate, population entropy, and perturbation theory.

This paper is concerned with the connection between two classes of population variables: measures of population growth rate--the Malthusian parameter, the net reproduction rate, the gross reproduction rate, and the mean life expectancy; and measures of demographic heterogeneity--population entropy. It is shown that the entropy functions predict the response of the growth rate parameters to perturbations in the age-specific fecundity and mortality schedule. These results are invoked to introduce the notion of environmental intensity. The intensity function, expressed in terms of the entropy parameters, is applied to give a comparative study of the effect of environmental factors on the dynamics of Swedish and French populations.

Age Factors↗
PubMed1998

Requisite mutational load, pathway epistasis and deterministic mutation accumulation in sexual versus asexual populations.

A measure of the equilibrium load of deleterious mutations is developed that explicitly incorporates the level of genome-wide linkage disequilibrium. This measure, called the requisite mutational load, is based on the minimal net reproductive rate of the least mutated class necessary to prevent the deterministic mutation accumulation. If this minimal net reproductive rate is larger than ecological or physiological constraints allow, then: a) the population is driven to extinction via deterministic mutation accumulation, or b) a mutational Red-Queen ensues with adaptation counterbalancing mutation accumulation. Two population parameters determine the requisite mutational load: a) the equilibrium strength of selection, measured as a selection gradient, and b) the equilibrium opportunity for selection, measured as the variance in number of mutations per genome. The opportunity for selection is decomposed into the accumulation of mutations (average number per genome) and the level of genome-wide linkage disequilibrium. Recombination can substantially reduce the requisite mutational load, compared to clonal reproduction, when there is buffering and/or reinforcing epistasis and also when there is positive assortative mating for fitness. Recombination is advantageous because it reduces the negative (variance reducing) linkage disequilibrium induced by beneficial epistasis. The functional form of the expression for requisite mutational load illustrates why epistasis within pathways, i.e., among closely interacting genes, is a powerful alternative to genome-wide truncation selection, as a means of reducing mutational load.

Animals↗
PubMed1994

[An analysis of Korean women's reproductivity].

An analysis of reproductivity is mainly concerned with the measurement of net force of fertility expressed in terms of a generation rather than in a given year. The present study examined current trends of Korean Women's reproductivity interpreting general reproduction and net reproduction rates, intrinsic rate of natural increase and mean length of gestation. The data used for this analysis were drawn from the national fertility surveys from 1970 through 1990 conducted by the Korea Institute for Population and Health. The figures of the present study revealed that the reproduction rates of Korea during the last 20 years decreased from 2.22 in 1970 to 0.71 in 1990 and net reproduction rates also dropped from 1.9 to 0.69 during the same period of time. Furthermore, from this study, it is noticed that the replacement level of fertility had been reached since the early 1980s. The intrinsic rate of natural increase as measure of population growth under existing conditions of fertility and mortality and free of the influence of the current age distribution, is computed. The level of rate was not much changed and was 0.3 in 1970 compared with 0.25 in 1990, which is still higher than other developed countries. The mean age of mother at the birth of their daughters defined as the length of generation has been slightly changed from 23.9 in 1971 to 25.8 in 1990.

Age Factors↗
PubMed2002

Evolution of flowering strategies in Oenothera glazioviana: an integral projection model approach.

The timing of reproduction is a key determinant of fitness. Here, we develop parameterized integral projection models of size-related flowering for the monocarpic perennial Oenothera glazioviana and use these to predict the evolutionarily stable strategy (ESS) for flowering. For the most part there is excellent agreement between the model predictions and the results of quantitative field studies. However, the model predicts a much steeper relationship between plant size and the probability of flowering than observed in the field, indicating selection for a 'threshold size' flowering function. Elasticity and sensitivity analysis of population growth rate lambda and net reproductive rate R(0) are used to identify the critical traits that determine fitness and control the ESS for flowering. Using the fitted model we calculate the fitness landscape for invading genotypes and show that this is characterized by a ridge of approximately equal fitness. The implications of these results for the maintenance of genetic variation are discussed.

Biological Evolution↗
PubMed1985

Lifetime (seven years) production of 1/4 and 1/2 Finnish Landrace ewes from Rambouillet, Targhee and Columbia dams under range conditions.

Lifetime lamb and wool production of 1/4 and 1/2 Finnish Landrace (Finn) crossbred ewes in comparison with local purebred controls was evaluated under range conditions. A total of 1,234 ewe lambs, representing nine breed groups, were first exposed to breeding at 7 mo of age and subsequently retained with no artificial culling, except for debilitating unsoundness, through 7 yr of production. Mating was to Suffolk sires. Differences among pooled breed groups (1/4 Finns, 1/2 Finns and purebreds) generally were not significant for ewe viability to lambing, percentage of lambs born alive and lamb viability to weaning; nor were differences significant for fertility except among yearlings (12 mo at lambing) where 1/4 and 1/2 Finn fertility exceeded that of purebreds by 217 and 278%, respectively. However, for prolificacy, Finn-crosses were consistently superior to purebreds at all seven ages; 1/4 and 1/2 Finns averaged 24 and 48% higher, respectively, than purebreds. Further, Finn-cross ewes clearly excelled purebreds (P less than .05) in the two overall measures of reproduction--net reproductive rate and weight of lamb weaned. The superiority was sustained through all ages and averaged (over ages 2 through 7 yr) 29 and 49% for net reproductive rate and 24 and 41% for weight weaned, for 1/4 and 1/2 Finns, respectively. Conversely, for wool weight, purebreds were consistently superior at all ages; the lifetime averages of 1/4 and 1/2 Finn fleeces were only 90 and 77% as high, respectively, as those of purebreds. It was concluded, however, that the loss in value of wool production associated with Finn breeding was economically of much less importance than the gains made in weight of lamb weaned. The use of 1/4 and 1/2 Finn-crosses involving the above adapted domestic breeds increased the net value of lifetime production by approximately 18 and 29%, respectively.

Animals↗
PubMed2001

Effects of salinity, temperature and food level on the demographic characteristics of the seawater rotifer Synchaeta littoralis Rousselet.

A strain of the seawater species Synchaeta littoralis, isolated from a Spanish Mediterranean coastal salt marsh, was cultured in the laboratory and fed with the alga Tetraselmis sp. The effect of three salinities (25 per thousand, 30 per thousand and 35 per thousand), two temperatures (20 degrees C and 25 degrees C) and two food levels (75,000 and 150,000 cells ml(-1)) on demographic parameters was studied using a life table approach. Average lifespan (LS) ranged between 4.0 and 7.3 days, net reproductive rate (R(0)) between 4.2 and 9.1 offspring per female, and intrinsic growth rate (r) between 0.50 and 0.95 day(-1). Salinity and temperature had a significant negative effect (***p<0.001) on both average lifespan (LS) and net reproductive rate (R(0)). Nevertheless, S. littoralis grew adequately at 35 per thousand (average value of r=0.67 day(-1)). Intrinsic growth rate also increased with temperature due to the lower value of the generation time (ranged between 2.3 and 3.8 days in all assays). Food level only had a significant negative effect (***p<0.001) on R(0). The experiments designed allowed us to know the basic demographic parameters of S. littoralis.

Journal Article↗
PubMed1991

Effects of inbreeding on reproduction and wool production of Rambouillet, Targhee, and Columbia ewes.

Because of a traditional interest in inbreeding as a tool for breed improvement, it was desirable to evaluate the effects of inbreeding on the most important products of the sheep industry, lamb and wool production. The data for this study were based on 13,807 ewe and 16,470 lamb records from Rambouillet (R), Targhee (T), and Columbia (C) sheep collected over 9 or 10 yr from 54 inbred lines. Average inbreeding of the lambs and ewes involved was near 25 and 20%, respectively. The combined effects of lamb's and dam's inbreeding reduced litter weight weaned at 120 d approximately .5 kg for each percentage of increase in inbreeding in every breed. For ewes and lambs of average inbreeding, the reductions relative to noninbred ewes amounted to 12.4, 10.3, and 11.3 kg for R, T, and C, respectively. The reductions constituted declines in weight weaned per ewe of 34, 25, and 28%. Similarly, net reproduction rate (lambs weaned per ewes put into breeding) was reduced more than one percentage point for each percentage of increase in inbreeding, with net declines at average inbreeding of 31.7, 23.5, and 25.7 percentage points for each breed, respectively. These reductions were equivalent to reductions in net rate of 29, 20, and 23%. The combined effect of lamb and dam inbreeding reduced weaning weight by 3.5, 2.6, and 2.2 kg, which constituted reductions of 10, 7, and 6%, respectively. Reduced weaning weight was approximately 30% as important as reduced net reproduction rate in contributing to the decline in litter weight weaned. Effects on fleece weight were curvilinear and amounted to reductions of .35, .18, and .00 kg, respectively, at levels of average inbreeding; however, Columbia fleece weights declined rapidly at levels exceeding 20% for ewes. Potential selection differentials were reduced 16% at inbreeding levels of 25 and 20% for lambs and dams, respectively, and 62% at levels of 55 and 50%. The average economic loss per ewe in value of production was estimated at $17 for average inbreeding and as high as $36 for inbreeding approaching 50%. It seems that the use of inbreeding as a tool for improving productive merit in sheep is much more certain to be a detriment, economically and genetically, than an advantage.

Animals↗