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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↗
PubMed2006

Life tables and development of Bemisia argentifolii (Homoptera: Aleyrodidae) at different temperatures.

The life history of Bemisia argentifolii Bellows & Perring (Homoptera: Aleyrodidae) on tomato (Lycopersicum spp.) was studied based on the age-stage, two-sex life table at 15, 20, 25, 28, 30, and 35 degrees C. The intrinsic rate of increase (r) at these temperatures is -0.0176, 0.0667, 0.1469, 0.1611, 0.1745, and 0.0989 d(-1), respectively. The relationship among the gross reproductive rate (GRR), the net reproductive rate (R0), and the preadult survivorship (l(a)) is consistent with GRR > l(a) x GRR > R0 for all results at different temperatures. The mean generation time is 81.9, 48.6, 28.4, 25.3, 22.1, and 18.2 d, respectively. The developmental rate of the egg stage at different temperatures fit a linear equation with a thermal summation 89.2 degree-days and a developmental threshold of 11.4 degrees C. The developmental rates of the nymphal stage fit the model of Stinner et al. and the parameters of C, Rmax, k1 and k2 were 0.085, 0.0833, 5.298, and -0.263, respectively.

Age Factors↗
PubMed2004

[Effect of temperature and food concentration on the population dynamics of three Brachionus calyciflorus strains].

Effects of temperature (20 degrees C, 25 degrees C, 30 degrees C) and food concentration (1.5, 3.0, 6.0, 9.0 x 10(6) cells x ml(-1)) on the population dynamics of Brachionus calyciflorus of Qingdao, Wuhu and Guangzhou strains were studied by means of individual culture. The result showed that the temperature was an important factor affecting generation time and intrinsic rate of population increase. With rising of temperature, the intrinsic rate of population increase increased, but generation time decreased. There were significant effects of food concentration on life expectancy and average lifespan. The effect of strain on net reproductive rate, generation time, life expectancy and average lifespan was also significant. Net reproductive rate, generation time, life expectancy, and average lifespan of Guangzhou strain was all the maximum, and that of Wuhu strain minimum among the three strains. The rotifers fed on the algae at the concentration of 3.0 x 10(6) cells x ml(-1) had the longest life expectancy and average lifespan, but those at 9.0 x 10(6) cells x ml(-1) had the shortest. Net reproductive rate, generation time, gross reproductive rate, life expectancy, and average lifespan of the three strains decreased linearly with the rise of temperature, except for the net reproductive rate of Guangzhou strain, while the intrinsic rate of population increase of all the three strains and gross reproductive rate of Guangzhou strain increased linearly with the rise of temperature. The relationships between all the life history parameters of Qingdao and Guangzhou strains and food concentration were all curvilinear, however, those between generation time, average lifespan, and life expectancy of Wuhu strain and food concentration could all be described by linear regression.

Animals↗
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↗
PubMed2003

Demographic changes in Daphnia pulex (Leydig) after exposure to the insecticides spinosad and diazinon.

The toxicity of the natural insecticide spinosad was assessed against Daphnia pulex (Leydig) using a demographic approach. Data were also generated for the commonly used organophosphorus insecticide diazinon as a comparison. Exposure to spinosad led to a concentration-dependent decline in survival, birth rate (b), net reproductive rate (R(0)), and intrinsic rate of increase (r(m)). Population extinction (-r(m)) occurred after exposure to spinosad concentrations >10 microg/L for 8 days. Exposure to increasing diazinon concentrations led to an initial increase in R(0) and r(m) followed by a sharp decline, with extinction occurring after exposure to >2 microg/L after 2 days. Based on concentrations of pesticide that caused population extinction, spinosad was five times less toxic than diazinon. The stable age distribution (after 65 days) of D. pulex changed after exposure to spinosad and diazinon. Increasing concentrations of spinosad resulted in a decrease in the percentages of individuals in the first juvenile and adult stages, increase in the third and fourth juvenile stages, and little or no change in the second juvenile and adolescent stages. Diazinon had a different effect on stable age distribution. Increasing concentrations of diazinon resulted in an increase in percentages of individuals in the first and second juvenile stages, little or no change in the third and fourth juvenile stages and adolescent stage, and a decrease in the adult stage. Although spinosad and diazinon are both neurotoxins, they have different modes of action and populations of D. pulex reacted differently to each pesticide. Results of this study indicate that spinosad is significantly less toxic than diazinon to D. pulex and because it is applied at lower concentrations than diazinon it should be less hazardous to this species.

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↗
PubMed1987

An assessment of the chronic toxicity of the synthetic pyrethroid, fenvalerate, to Daphnia galeata mendotae, using life tables.

The effects of chronic exposure to fenvalerate, a synthetic pyrethroid insecticide, on the cladoceran Daphnia galeata mendotae were evaluated under laboratory conditions. The daphnids were exposed for their entire life cycle to concentrations ranging from 0.005 to 0.1 microg fenvalerate litre(-1). The parameters used to determined toxicity were survival, time to first reproduction, reproductive frequency, number of young per brood, cumulative brood size, intrinsic rate of natural increase (r(m)), generation time (T) and net reproductive rate (R(0)). A concentration of 0.005 microg fenvalerate litre(-1) resulted in an increase in longevity but a decrease in production of young. Higher concentrations caused a decrease in survival. Studies of shorter duration than the complete life cycle of the organisms would not have detected toxicity at such low levels. The intrinsic rate of natural increase, r(m), was not affected by fenvalerate until concentration reached 0.05 microg litre(-1) and r(m) decreased to 0.113 from 0.238. A concentration of 0.01 microg litre(-1) caused the net reproductive rate, R(0), and the generation time, T, to decrease to 73.2 offspring per female and 17.3 days from 125.9 offspring per female and 20.3 days, respectively.

Journal Article↗
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↗