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PubMed1994

Age composition, natural survival and population growth of Anopheles fluviatilis James, 1902, the major malaria vector in the endemic belt of Koraput District, Orissa, India.

The population growth of Anopheles fluviatilis, the major malaria vector, was studied in the hill tracts of Koraput district. Immature duration ranged from 11 to 14 days (mean = 12.42 +/- 0.99) in rainy and 12 to 17 days (mean = 14.78 +/- 1.64) in cold season. The probability of immature survival through different developmental stages was maximal in ponds. Daily survival rate of adults fluctuated between 0.55 and 0.92. The net reproductive rate (Ro) was estimated to be 3.0200 for cold and 0.6486 for rainy season. The mean generation time (T) was slightly longer in cold season (22.32 days) than rainy season (21.24 days). The intrinsic rate of population increase (rm) and consequently the finite rate of increase (lambda) were estimated for cold and rainy seasons. Population growth based on adult resting density was also assessed for different seasons.

Age Distribution↗

PubMed1992

Temperature influence on life table statistics of the chicken mite Dermanyssus gallinae (Acari: Dermanyssidae).

An age-specific life table for the chicken mite Dermanyssus gallinae (DeGeer, 1778) was based on various observations carried out at 25 degrees C. The generation time was calculated to be 16.8 days; the intrinsic rate of natural increase was 0.12 per day, and the net reproductive rate was 7.2. A nonlinear function was found satisfactory to describe the developmental rate of the different immature life-stages at temperatures below 40 degrees C. The stage-specific survival of the immature life-stages was generally high between 10 and 37 degrees C, but decreased quickly outside this temperature range. Most of the eggs were laid during the first three weeks of the adult life. The proportion of surviving females rapidly decreases after moulting to the adult stage. At a temperature of 30 degrees C, the highest number of eggs (3 eggs per day) was laid.

Animals↗

PubMed1976

Influence of instantaneous fertility decline to replacement level on population growth: an alternative model.

If age-specific birth rate mx of a stable population drop abruptly to mx/Ro, where Ro is the net reproduction rate, then, according to Keyfitz, the size of the ultimate stationary population relative to that at the beginning of the process is given by I = beoo(Ro - 1)/(rmuRo), where b and r are the birth rate and the rate of growth, respectively, of the stable population, eoo the life expectancy at birth, and mu the average age at childbirth in resulting stationary population. Noting that the decline in mx need not necessarily be uniform, investigation has veen carried out to examine the effect on I when fertility decline is more rapid at higher ages. In particular, the effect of the reduced age-specific rates such as mxe-rx (which also produces a stationary population) has been analyzed, and simplifications of the results carried out separately for three different models of the net maternity function. It has also been shown the when mx drops abruptly to some m* x, where the form of m*x need not be specified except for the restriction that the resulting population will be stationary, the value of the index can be approximately obtained from I* = beoo (1 - rmu/2), where mu is the average age at childbearing of theinitial stable population.

Birth Rate↗

PubMed1991

A true rate of population growth--Lotka's intrinsic rate of natural increase revisited.

In this paper, Lotka's intrinsic rate of current population growth is evaluated. A new method of computing the net reproduction rate and a new rate of population growth are proposed. The proposed rate is the rate of growth of the female population per woman per year. The rate is positive, equal to zero, or negative as a population is increasing, remaining stationary, or decreasing. The rate for the 1987 U.S. white female population was R = -0.0037. This means that the white population was decreasing in 1987 and was losing 3.7 females for every 1000 women per year.

Female↗

PubMedDate not supplied

Colonization and laboratory maintenance of Anopheles albimanus Wiedemann in Venezuela.

Anopheles albimanus is one of the main vectors of malaria in Central America and the Caribbean, based on its importance, there are previous reports of the successful colonization of this species in Latin America countries. Mosquitoes were collected in the Aragua State of Venezuela colonized in the laboratory, using a simple and efficient maintenance method. Based on life table calculations under well established laboratory conditions, the Survival Rate Probability was constant and always close to 1 in immature stages, the Reproductive Net Rate (Ro) was 3.83, the generation time (Tc) was 24.5 days and the Intrinsic Growth Rate (rm) was 0.0558. This is the first report of the colonization of A. albimanus in Venezuela.

Animals↗

PubMed1978

The momentum of population growth with time dependent net maternity function.

The momentum of population growth problem of Keyfitz is generalized to contain a gradual change of the age-specific birth rate ro the level of bare replacement. Assuming a time dependence for the net maternity function of the form (formula: see text) R being the net reproductive rate, we show that for the Malthusian model the asymptotic birth rate is increased by exp (r/lambda), where r is the rate of increase of the population before t = 0. A numerical method for obtaining the asymptotic birth rate for a general net maternity function with the same time dependence is outlined.

Age Factors↗

PubMed1997

[Population parameters of three parasitoids (Hymenoptera: Scelionidae, Encyrtidae) hosted by the predator Podisus nigrispinus (Heteroptera: Pentatomidae)].

The reproductive parameters of Telenomus podisi, Trissolcus brochymenae (Hymenoptera: Scelionidae) and Ooencyrtus sp. (Hymenoptera: Encyrtidae) were studied for three generations on their natural host Podisus nigrispinus (Dallas, 1851) (Hemiptera: Pentatomidae). A parasitism rate of 10 eggs/day/species was used under laboratory conditions of 27 +/- 1 degrees C, 60 +/- 10% RH and 14 h of photophase. No significant differences were detected between generations in terms of net reproductive rate (Ro), intrinsic rate of natural increase (rm), generation time (T) and the effect of doubling time on population increase (DT). However, T. podisi and T. brochymenae had significantly higher Ro and rm values, and lower T and DT values, with rm 1.59 and 1.50 times higher than Ooencyrtus sp., respectively. In addition the former species also had shorter egg-adult period, greater longevity of females and reproduction period than the other species. These results confirm the greater reproductive potential of T. podisi and T. brochymenae, which are commonly found parasitizing P. nigrispinus.

Animals↗

PubMed2001

Development, survival and reproduction of black citrus aphid, Toxoptera aurantii (Hemiptera: Aphididae), as a function of temperature.

The development, survival, and reproduction of the black citrus aphid Toxoptera aurantii (Boyer de Fonscolombe) were evaluated at ten constant temperatures (4, 7, 10, 15, 20, 25, 28, 30, 32 and 35 degrees C). Development was limited at 4 and 35 degrees C. Between 7 and 32 degrees C, developmental periods of immature stages varied from 44.2 days at 7 degrees C to 5.3 days at 28 degrees C. Overall immature development required 129.9 degree-days above 3.8 degrees C. The upper temperature thresholds of 32.3, 28.6, 29.3, 27.2, and 28.6 degrees C were determined from a non-linear biophysical model for the development of instars 1-4 and overall immature stages, respectively. Immature survivorship varied from 82.1 to 97.7% within the temperature range of 10-30 degrees C. However, immature survivorship was reduced to 26.3% at 7 degrees C and 33.1% at 32 degrees C. Mean adult longevity was the longest (44.2 days) at 15 degrees C and the shortest (6.2 days) at 32 degrees C. The predicted upper temperature limit for adult survivorship was at 32.3 degrees C. Total nymph production increased from 16.3 nymphs per female at 10 degrees C to 58.7 nymphs per female at 20 degrees C, declining to 6.1 nymphs per female at 32 degrees C. The estimation of lower and upper temperature limits for reproduction was at 8.2 and 32.5 degrees C, respectively. The population reared at 28 degrees C had the highest intrinsic rate of increase (0.394), the shortest population doubling time (1.8 days), and shortest mean generation time (9.5 days) compared with the populations reared at six other temperatures. The population reared at 20 degrees C had the highest net reproductive rate (54.6). The theoretical lower and upper temperature limits for population development, survival and reproduction were estimated at 9.4 and 30.4 degrees C, respectively. The biology of T. aurantii was also compared with three other citrus aphid species.

Animals↗

PubMed1997

A comparison of acute mortality and population growth rate as endpoints of toxicological effect.

The objective of this study was to determine how closely acute (72-hr) lethal concentration estimates developed from probit analysis compared to the demographic toxicological endpoints, net reproductive rate (Ro), the intrinsic rate of increase (rm), and realized fecundity (Ux), in terms of predicting effects of pesticides on populations. Lethal and sublethal effects of the insecticide imidacloprid on the arthropod Acyrthosiphon pisum Harris (pea aphid) were determined for populations exposed to foliar-sprayed broad bean Vicia faba L. (variety Banner). An examination of Ro indicated that sublethal effects were occurring that reduced reproduction. However, by looking at the mean number of offspring produced per surviving female and Ux, it was determined that the reduction in Ro was entirely due to acute mortality and a reduction in life span. Also, exposure to increasing concentrations of imidacloprid did not cause a shift in either the day of initial reproduction or the day of peak reproduction. Therefore, this pesticide caused no sublethal effects on reproduction and, as such, a lethal concentration estimate should have been a good predictor of effect at the population level. However, the 72-hr lethal concentration estimate was not a good predictor of effect of this pesticide on population growth. Populations exposed to the 72-hr LC60 were able to maintain rates of population increase (rm = 0.224) similar to those of the control (rm = 0.295). The data indicate that the reason for the discrepancy between acute lethal concentration estimates and population growth was that surviving individuals were able to sustain heightened rates of reproduction following acute exposure to imidacloprid. The ability of surviving individuals to maintain these high reproductive rates allowed them to compensate for losses and act as reservoirs for future reproduction. It is not possible, using acute mortality estimates alone, to predict this "reservoir effect," and therefore not possible to predict how a population's growth rate will respond or change based on this endpoint. Thus this would suggest that the assessment of a xenobiotic based solely on acute mortality estimates will lead to flawed conclusions about a population's exposure response.

Animals↗

PubMed1987

Laboratory rearing techniques and adult life table parameters for Anopheles sergentii from Egypt.

Techniques are presented for maintaining colonies of Anopheles sergentii, an important malaria vector in Egypt. Larval development time and survival rates were determined for 3 rearing solutions and 4 temperatures. Under optimal conditions larval survival rates averaged 85%. Mean life expectancy at emergence for mated An. sergentii was 23.3 days under insectary conditions of 27 +/- 2 degrees C, 70-80% R.H. The net reproductive rate, mean generation time and instantaneous rate of increase were respectively, 45.8 females per female per generation, 29.7 days and 0.127. In the context of vector potential for malaria transmission, An. sergentii has a daily survivorship rate of 0.95.

Actuarial Analysis↗

PubMed1976

Some extensions of the Keyfitz momentum relationship.

A stable population, such that the total birthrate B(t) = Boerot, is abruptly altered by modifying the age-specific birth rate, m(x). The survivor function remains unaltered. The modified population ultimately settles down to a stable behavior, such that B(t) = B1er1t. It is shown that B1/Bo = (Ro-R1)/¿e1(ro-r1)RoZ1], where Ro, R1 are the net reproduction rates before and after the change, and Za = expected age giving birth for the stable population after the change. The age structure and transients resulting from the change are also described. The effect of an abrupt change in the survivor function l(x) is also investigated for the simple case where the change is caused by altering l(x) to e-lambdaxl(x). It is shown that the above ratio becomes B1/Bo = N1/No = [1 - zota o e-kxg(x)dx]/Z1lambda, where N refers to the numbers in the population, k = ro + lambda, and g(x) = m(x)l(x), the value before the change. A measure for the reproductive worth of the population is also established.

Birth Rate↗

PubMed1994

The influence of additive and nonadditive gene action on lifetime yields and profitability of dairy cattle.

Additive and nonadditive genetic effects on lifetime yields of milk and milk components and lifetime profitability were estimated from 5070 cattle in a Holstein pureline, an Ayrshire-based pureline, and 10 crossbred groups of these purelines. Lifetime yields of milk, fat, protein, and lactose and lifetime milk value and annualized discounted net returns were analyzed. Lifetime yields, lifetime milk value, and annualized discounted net returns of the Holstein x Ayrshire-based line F1 and an F1 x (F1 x F1) cross were not significantly different from those for the Holstein pureline. Net reproductive rate for F1 females was 9% greater than that of contemporary Holsteins. The Holstein pureline was superior to the Ayrshire-based pureline for direct additive genetic merit for all traits. Heterosis for the lifetime traits ranged from 16.6% for lifetime milk yield to 20.6% for annualized discounted net returns. Cytoplasmic maternal effect on annualized discounted net return was significant and favored the Ayrshire-based line. Potential economic benefit may derive from development of a crossbred cow that is superior to Holsteins. Maximum exploitation of additive and nonadditive genetic effects on lifetime yields and profitability appears to favor a rotational crossbreeding system with two breeds.

Animals↗

PubMed2002

The juvenile growth rate of Daphnia: a short-term alternative to measuring the per capita rate of increase in ecotoxicology?

The juvenile growth rate (gj) of Daphnia is a good predictor of the per capita rate of increase (r), which is considered the ecologically most meaningful parameter. The hypothesis is tested that gj may be used as a surrogate for r in short-term ecotoxicological tests to replace the time-consuming population-based testing. The effects of 3,4-dichloroaniline (DCA) on various reproductive parameters of Daphnia magna, including r, net reproductive rate in 21 days (R21), age at first reproduction (AFR), adult survival, and egg viability, were measured simultaneously with gj. Reproductive parameters were not affected below a concentration of 9 microg/L DCA, but all of them responded strongly above this concentration. DCA reduced the total number of eggs produced only moderately, but induced strong egg mortality in particular in the first brood. Because egg mortality is an important factor, measures of sublethal toxic effects must be based on viable eggs. Although (g) is a good predictor of individual fitness of Daphnia under variable natural conditions when egg mortality is negligible, it is not a good predictor of the effects of xenobiotic stress; hence it cannot replace r. Short-term tests based solely on either somatic growth or egg viability are not sufficiently correlated with r to give ecologically meaningful results, but protocols based on the number of viable eggs in the first clutch and the time to release of the first neonates may be an alternative to the 21-day test or longer life-table experiments.

Animals↗

PubMed2002

[Population growth rate of the depredating Podisus nigrispinus (Heteroptera: Pentatomidae) and of the Tuta absoluta (Leptoptera: gelechiidae) in wintering place].

The fertility life table of Podisus nigrispinus (Dallas) (Heteroptera: Pentatomidae) preying either on Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) caterpillars or on alternative prey Tenebrio molitor L. (Coleoptera: Tenebrionidae) under greenhouse conditions (30 +/- 5 degrees C, 61 +/- 23% RH) were studied. The life table was also determined for the pest T. absoluta under the same conditions. The net reproductive rate (Ro) and the intrinsic rate of natural increase (rm) were higher 14.13 and 46.32 times for predators fed on T. molitor prey, however, the generation time (T) was similar between prey. The pest T. absoluta showed Ro and rm higher 2.15 and 32.10 times than those achieved for predators fed on this pest. However, females fed on a suitable prey T. molitor showed higher Ro and rm than those yielded for the pest. The survival curves were similar for P. nigrispinus females fed on both prey and classified as being type II by Weibull analysis. The results suggest that P. nigrispinus is able to maintain its population preying only on T. absoluta caterpillars; however, the life table parameters determined individually for both showed that the pest produces more generations per year and faster population natural growth than the predator.

Animals↗

PubMed1984

About Laplace transforms of the distribution of births in the initial population with unchanging net maternity rates.

"The solutions of the integral equation for the stable population by Laplace transform have been examined by shifting the origin from t=0 to other points in time. The relationship between the birth functions generated by the initial populations measured from different points of time has been found to be very simple and straight forward." The author also shows "that for a stable population, the total number of births in the next generation can be expressed as a simple function of the net reproduction rate, the intrinsic rate of growth and number of births at the beginning of the process. For the stationary population, the same relationship simplifies even further and is given in terms of the product of the number of births at the beginning of the process and the average age of motherhood."

Age Factors↗

PubMed1998

Responses to various selection protocols for lamb production in Rambouillet, Targhee, Columbia, and Polypay sheep.

To investigate the effectiveness of four selection protocols for improving reproduction in sheep, we evaluated nine selection lines and two random-bred control lines for lamb and wool production. Results were based on 25,026 dam and 30,628 lamb records from Rambouillet (R), Targhee (T), Columbia (C), and Polypay (P) sheep collected from 1976 through 1988. Phenotypic trends over years were positive (P < .01) for most reproductive traits, body weight, wool grade (coarser grades), and lamb weaning weight in nearly all selected lines. Small positive trends for both random-bred control lines indicated there were improvements in management and(or) environment during the period. Small but significant phenotypic declines in fleece weights occurred in most lines, including controls. Substantial genetic gains (P < .01) in litter weight weaned (120 d), net reproductive rate (lambs weaned divided by ewes mated), prolificacy, body weight, and weaning weight were made in nearly all selected lines. There were also small but significant improvements in milk score in most lines. There were significant genetic declines and improvements in fleece weights; however, the average genetic change in fleece weight for lines selected for litter weight weaned was negligible. Genetic improvement in litter weight weaned was attributed approximately 37% to prolificacy, 27% to percentage of lambs weaned, 17% to lamb weaning weight, 12% to fertility, and 7% to ewe viability from breeding to lambing. On average, selection based on independent culling levels (litter weight weaned plus yearling body weight), yearling body weight, or early puberty was only 85, 67, or 59%, respectively, as effective as that based solely on litter weight weaned for improving litter weight weaned. The net value of the average (over all breeds) annual increase in production per ewe resulting from selection for litter weight weaned accumulated over 12 yr to an estimated $11.40 and $21.51 annually for genetic and phenotypic increases, respectively.

Animals↗

PubMedDate not supplied

Influence of water extracts from the surface of two yew (Taxus) species on mites (Tetranychus urticae).

Taxus cuspidata and Taxus media var. Hicksii contain paclitaxel, among other taxoids, on the surface of the needles. These compounds were removed by 5-s dipping of the needles in water just below its boiling point at 96 degrees C and at 60 degrees C and 40 degrees C. Taxus cuspidata contained a fourfold higher concentration of paclitaxel than Taxus media var. Hicksii. The extract with the higher concentration of paclitaxel was more harmful to the mites Tetranychus urticae Koch, increasing their mortality 150%, prolonging development by ca. 20% and lowering the average fecundity from 112 in the control to 16.13 after treatment with Taxus cuspidata; also, the net reproductive rate dropped from 70.24 to 6.70, which is more than a tenfold reduction.

Animals↗

PubMed2002

Food concentration affects the life history response of Ceriodaphnia cf. dubia to chemicals with different mechanisms of action.

The effect of three chemicals with different mechanisms of action (3,4-dichloroaniline, fenoxycarb, and chlorpyrifos) on the life history response of the cladoceran Ceriodaphnia cf. dubia was examined under both limited (3 x 10(4) cells/mL) and abundant (15 x 10(4) cells/mL) food conditions. Toxicity tests were conducted at both food concentrations simultaneously for each chemical, and cladocerans were examined daily from less than 24 h old until their death. A range of life history parameters were calculated, including mean brood sizes, survival, net reproductive rate, and population growth rate. The toxicity of 3,4-dichloroaniline was not significantly affected by food concentration. However, limited food significantly decreased the toxicity of fenoxycarb, and significantly increased the toxicity of chlorpyrifos. The effect of food concentration on toxicity appears to depend on the mechanism by which the chemical exerts its toxicity and on food--chemical interactions. Possible mechanisms for the different effects of food concentration on toxicity are discussed.

Aniline Compounds↗