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At least 127 records · Page 7Linked to original sources
PubMed1991

Momentum and the growth-free segment of a population.

In the scenario of a sudden drop in fertility to replacement level. Preston (1986) argued that the population segment under age T, the length of generation, remained growth-free. Here we first present a new relationship for the momentum of any observed population as the ratio of 1) the proportion of the observed population under the mean age at childbearing to 2) the proportion of its life table population under that mean age. We then use that relationship to demonstrate Preston's approximation. Growth factors for other population segments are also presented. When the initial population is stable, momentum can be approximated as a function of the net reproduction rate alone.

Age Factors↗
PubMed1987

Studies on autogeny in Culex tarsalis: 3. Life table attributes of autogenous and anautogenous strains under laboratory conditions.

The reproductive biology and life table attributes of autogenous and anautogenous strains of Cx. tarsalis which were selected from the same parent colony were compared under laboratory conditions. Autogenous mosquitoes required 1 day longer to complete immature development, but oviposited 1 to 2 days earlier than anautogenous mosquitoes. Autogenous females readily imbibed blood meals from restrained chickens if ovarian maturation had not progressed to Christophers' Stage III. Wing length and life expectancy were not significantly different between strains; however, autogenous females laid a significantly smaller number of eggs per raft during initial oviposition than anautogenous females. Egg raft size did not differ significantly between strains during subsequent ovipositions resulting in similar net reproductive rates (Ro). Earlier oviposition and a comparable Ro resulted in a greater intrinsic rate of increase (rm) and birth rate (b) for autogenous than anautogenous cohorts. Thus, highly autogenous populations would be able to exploit newly created surface water breeding sources more rapidly than highly anautogenous populations. However, highly autogenous populations probably would not be able to transmit a horizontally maintained arbovirus as efficiently as anautogenous populations, since autogenous females imbibe their initial blood meal later in life than anautogenous females.

Actuarial Analysis↗
PubMed1982

Immigration and the stable population model.

This paper reports on work aimed at extending stable population theory to include immigration. its central findings is that, as long as fertility is below replacement, a constant number and age distribution of immigrants (with fixed fertility and mortality schedules) lead to a stationary population. Neither the level of the net reproduction rate nor the size of the annual immigration affects this conclusion; a stationary population eventually emerges. How this stationary population is created is studied, as is the generational distribution of the constant annual stream of births and of the total population. It is also shown that immigrants and their early descendants may have fertility well above replacement (as long as later generations adopt and maintain fertility below replacement), and the outcome will still be a long-run stationary population.

Adolescent↗
PubMed1980

Laboratory colonization and life table statistics for geographic strains of Simulium decorum (Diptera: Simuliidae).

Colonization techniques were developed in order to select mating strains from four geographic populations of Simulium decorum. Although mating strains were established from each locale, emphasis was shifted toward developing permanent colonies from Dryden Lake, New York, USA and Warm Springs, Georgia, USA. The net reproductive rate (Ro) was computed for the parental, F1, and F2 generations of each strain in order to assess the effects of colonization through successive generations. Ro increased rapidly for both strains from parental (range of 0.34-3.5) through F2 generations (range of 16.2-21.6). Analysis of Ro components indicated that the increases in Ro were the result of two parameters that reflect the propensity of flies to mate in confinement, suggesting that selection for mating is rapid. Multiple regression analysis indicated no significant differences between strains or generations when tested against fecundity (range of 391-519) and survival of immatures (range of 90.3-97.2%). A slight positive correlation (regression coefficient of 0.0016, P less than .01) was observed between larval density (range of 284-4,439 larvae per rearing) and survival of immatures, suggesting that the limits of the rearing system with regard to crowding were not approached. Both strains readily adapt to the laboratory and are currently in the fifth generation.

Animals↗
PubMed1997

Effect of Eucalyptus feeding in the development, survival and reproduction of Tynacantha marginata (Heteroptera: Pentatomidae).

The effect of feeding on Eucalyptus leaves of Tynacantha marginata (Heteroptera: Pentatomidae) was studied in Brazil. The use of this plant as a complementary food source for the predatory bug increased its oviposition period, generation time, and net reproductive rate. Eucalyptus leaves apparently had no influence on the survival and development of T. marginata.

Animals↗
PubMed1997

Life-table attributes of Anopheles albimanus (Wiedemann) under controlled laboratory conditions.

The life-table attributes of a laboratory-colonized strain of Anopheles albimanus Wiedemann from El Salvador were investigated under controlled environmental conditions (26 +/- 2 degrees C, 60 +/- 2% RH, and 16:8 L:D photoperiod). Larvae pupated seven days after eclosion and the adults emerged on day eight. Adult emergence success was 91% and sex ratio was not significantly different from 1:1. Females took a blood meal one day after emergence and laid eggs two days later. The mean time of reproduction was 10.8 days and the expectation of life at emergence was 18.8 and 14.1 days for females and males, respectively. The daily survivorship of females at emergence was 0.97, and their net reproductive rate, age at mean cohort reproduction, instantaneous rate of increase, and mean generation time was 309.2, 10.8 days, 0.319, and 18 days, respectively. The life expectancy of females 10 days after emergence was 13.4 days, and they were capable of taking four to six additional blood meals.

Animals↗
PubMed1997

[Life tables of Blattella germanica (Dictyoptera: Blattellidae) under laboratory conditions and their importance for its control].

A study of the life tables of Blatella germanica (L.) 1767 was conducted under laboratory conditions. 3 treatments were used a according to the number of individuals in each breeding flask (A = 9 flasks with 20-25 individuals, B = 17 flasks with 30-35 individuals, and C = 30 flasks with a newly hatched nymph each). The main parameters of the population growth were calculated by the TABVID software . The respective values for treatments A and B were the following: net reproduction rate (Ro 2.23 and 2.37), natural increase finite rate (lambda = 1.06), natural increase intrinsic rate (r = 0.06), and mean generational time (T = 13.89 and 15.64). The behaviour of the survival probability by age, the fertility rate, and the mortality rate were graphically registered. Life expectancy for treatment C was 16.47 and the survival rate for this treatment was represented by a graph. Graphics of the growth curve of this species and of the survival rate for treatments A and B were shown. The latter was concave, which means that mortality is higher during the young stages. This study provides esential cuantitative basic date that allow to carry out a more efficient control if fight is directed to the period where the highest natural mortality was found, that is, at the step from nymph 6 to adult in treatments A and B.

Animals↗
PubMed1980

Effects of fertility and mortality on extinction of family and number of living children.

A model is developed to study the effects of fertility and mortality on number of living children and on extinction of family. Numerical illustrations are provided by applying the model to three different populations differing in fertility and mortality. It is found that a combination of a high birth rate and a low death rate is required to assure a reasonable probability that the family will not ultimately become extinct. A moderate to high birth rate and a low death rate are necessary to assure that there will be at least one surviving son in the parents' old age. This finding implies that zero population growth is impossible as long as parents depend on children for old age security. Thus, alternate old age security measures must be adopted by societies attempting to reduce their birth rate to the replacement level.

Family Characteristics↗
PubMedDate not supplied

Reproductive life of Bhoksa women.

The paper discusses the reproductive life of 111 ever-married Bhoksa women. The mean age at marriage for women of all ages among Bhoksas, like other tribal populations, is high, unlike the caste populations. The mean ages at first birth of the pooled sample and of the completed fertility cases suggest late and early marriages of the older and younger generations. The maximum number of marriages occur between 15 and 19 years and of first births between 16 and 20 years. Percentage of reproductive wastage is high in both the lower and higher age groups. Young mothers with low birth orders and older mothers with high birth orders display a high frequency of reproductive wastage. Evidently, both birth order and the age of the mother have effects on reproductive wastage. Average number of children ever born (including stillbirth but not abortion or miscarriage) per mother of all ages is the highest among Bhoksas of all the studied ethnic groups of India. The Bhoksa, like caste populations, show a high number of children ever born per mother of completed fertility. Quite a high masculinity in the secondary sex ratio, like other mongoloid population is noticed. The contribution of mortality component to the Total Index of Opportunity for Selection is more than that of the fertility component. Bhoksas conform to the general low range of net reproductive index, which is however greater than unity, suggesting that they are in a growth stage.

Age Factors↗