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PubMed2003

Population dynamics of small mammals in semi-arid regions: a comparative study of demographic variability in two rodent species.

The seasonally determined demographic structure of two semi-arid rodents, both agricultural pest species (the leaf-eared mouse (Phyllotis darwini) in Chile and the multimammate mouse (Mastomys natalensis) in Tanzania), is analysed using capture-mark-recapture (CMR) statistical models and measures for elasticity (the relative change in the growth rate due to a relative unit change in the parameter of concern) derived from projection linear matrix models. We demonstrate that reproduction and survival during the breeding season contribute approximately equally to population growth in the leaf-eared mouse, whereas the multimammate mouse is characterized by a more clearly defined seasonal structure into breeding and non-breeding seasons and that reproduction contributes far more than survival during the breeding season. On this basis, we discuss evolutionary and applied (pest control) issues. Regarding the evolution of life histories (leading to a maximization of the overall net annual growth rate), we suggest that for the leaf-eared mouse, features favouring survival throughout the year will provide selective value, but that during the main breeding season, features favouring reproduction and survival are about equally favourable. For the multimammate mouse, features favouring survival are particularly important outside the breeding season, whereas during the breeding season features favouring reproduction are more important. Regarding pest control (aiming at reducing the overall net annual growth rate), we suggest that (ignoring economic considerations) affecting survival outside the main breeding season is particularly effective for the leaf-eared mouse, a feature that is even more the case for the multimammate mouse. In sum, we demonstrate through this comparative study that much is to be learnt from studying the dynamics of fluctuating small rodents-a focal issue within much of population ecology.

Animals↗
PubMed1994

Conception rates. 1. Derivation and estimates for effects of estrus detection on cow profitability.

Objectives were to derive equations and obtain estimates per cow of days to conception, milk production, semen purchases, calvings, and reproductive failures based on the probability of estrus detection and AI conception. The net benefits of changing rates of estrus detection, including changes in milk production, semen purchases, and replacement inventories (culled cows and calves) were converted to annual values and multiplied by fixed prices to obtain estimates of the annual financial benefit of a change in rates of estrus detection. Improvement in milk production because of a 1-d decrease in DIM at conception was dependent on DIM, peak milk production, and monthly rate of decline in daily milk production. Variation was considerable in expected benefits of improved estrus detection. Under the assumption that replacement was not planned prior to breeding (in which case improved estrus detection would have no value), estimated financial benefits for increasing the probability of estrus detection from 60 to 70% with a 70% AI conception rate were $6/yr; increasing from 20 to 30% the rate of estrus detection with a 50% AI conception rate increased estimated annual benefits to $83. This wide range of values occurred with fixed costs and prices so that fluctuating prices would introduce further variation in financial benefits. Derived equations allow point estimates of expected benefits with input values estimated.

Animals↗
PubMed2004

Population consequences of fipronil and degradates to copepods at field concentrations: an integration of life cycle testing with leslie matrix population modeling.

The predominant data used in ecological risk assessment today are individual-based rather than population-based; yet environmental policies are usually designed to protect populations of threatened species or communities. Most current methods in ecotoxicology are limited by largely logistic/ technology-driven requirements that yield data for a relatively small number of test species and end points that focus on acute lethality or sublethal nonproduction-based parameters (e.g., biomarkers, mutagenesis, genetic change, physiological condition). A contrasting example is presented here showing the predictive ability of meiobenthos-based full life cycle toxicity testing to extrapolate multi-generational effects of chemicals on variables of import to population growth and maintenance. Less than 24-h-old larvae of a meiobenthic copepod were reared individually in 96-well microplate exposures to parent and degradates of the phenylpyrazole insecticide fipronil. Survival, development rates, sex ratio change, fertility, fecundity, and hatching success were tracked daily for 32 d through mating and production of three broods in spiked seawater. These data were then inserted in a Leslie (Lefkovitch) matrix stage-based population growth model to predict relative rates of population increase (lambda) and changes in net population growth with time and toxicant concentration. Field-reported test concentrations produced strong reproductive (52-88%) and net production (40-80%) depressions for parent (at 0.25 and 0.5 microg/L), desthionyl (0.25 and 0.5 microg/L), and sulfide (0.15 microg/L) moieties as compared to controls. Spiked sediment exposures of 65-300 ng of fipronil/g of dry sediment yielded significantly reduced production rates per female that were 67-50% of control production. The consistent reproductively linked impacts of fipronil and its degradation products at the population maintenance levels suggest risks to sediment-dwelling crustaceans at concentrations well below noneffects for most aquatic test species based on risk assessment data from primarily acute and sub-life cycle toxicity tests.

Animals↗
PubMed1996

Lack of association of bovine MHC class I alleles with carcass and reproductive traits.

The present study was carried out to examine whether a relationship between bovine major histocompatibility complex (BoLA) class I alleles and carcass traits or reproductive performance exists in Braunvieh and Fleckvieh AI (artificial insemination) bulls. The influence of BoLA class I (BoLA-A) alleles on deregressed breeding values for net growth rate, carcass index and thigh volume was assessed in Braunvieh crosses and Fleckvieh bulls with a gene substitution model. The reproductive traits: non-return rate and interval between first and last insemination of daughters (female fertility), as well as non-return rate of inseminated cows (male fertility), were only investigated in Fleckvieh animals. No influence of the BoLA-A region on the traits evaluated could be demonstrated. An improper, i.e. less restrictive analysis would have led to spurious results.

Alleles↗
PubMed1986

Fertility, embryo survival and litter size in lines of Targhee sheep selected for weaning weight or litter size.

Conception rate, prenatal survival and litter size were recorded for 444 ewes of two age groups from five lines of grade Targhee sheep: two unselected control lines, HC1 and DC(C); two lines selected for 20 yr for increased 120-d weight, HW and DH(W); and a line selected for 18 yr for increased multiple births, T. Line T was equal or superior to the control lines in conception rate, prenatal survival and litter size in both age groups, although most of the differences were not significant. The W selected lines were inferior to the C and T lines in fertility and tended to be lower in prenatal survival, among mature ewes, resulting in a significantly lower number of lambs born per corpus luteum in the W lines than in the other two groups. Among yearlings, C ewes were non-significantly lower in fertility than T and W ewes, while W ewes were significantly lower than C and T ewes in prenatal survival. The T line ewes had higher overall reproductive performance than either of the other two groups. Ewes with two ovulations had a significantly higher conception rate than ewes with single ovulations. Gestation period was exceptionally uniform with a coefficient of variation of 1.3% and little difference due either to line or litter size. It was concluded that selection for multiple births improved overall reproductive performance, whereas selection for increased growth rate had an adverse effect on several components of reproduction, leading to a net decline in fitness.

Animals↗
PubMed2000

Optimization of dairy heifer management decisions based on production conditions of Pennsylvania.

We used a dynamic programming model to determine optimum rearing decisions of dairy replacements. Heifers were described in the model by age, season, body weight, pregnancy state, and prepubertal growth rate. Prices and parameters were chosen to represent the dairy population of Pennsylvania. We calculated monthly costs and revenues from calf value, feed costs, veterinary costs, semen costs, carcass value, and full-grown heifer value. The model considered a stochastic variation in the onset of puberty, conception, involuntary disposal, and a seasonal variation in the prices of calves, heifers, and feed. Based on a critical prepubertal average daily gain of 0.9 kg/d and a maximum achievable postpubertal growth rate of 1.1 kg/d, the optimum practice resulted in an average age at first calving of 20.5 mo at a body weight of 563 kg. Discounted net returns equaled $107 per heifer per year. The optimum rearing practice was not sensitive to seasonal variation in prices. Nevertheless, the economic results per season of birth varied considerably; the highest income per heifer was obtained from heifers born in December ($142/yr), whereas those born in May yielded the lowest ($100/yr). Sensitivity analyses demonstrated a considerable influence of growth rate restrictions and variation in reproductive performance on both the optimal rearing practices as the expected net returns.

Animal Feed↗
PubMed2002

Demographic responses of the polychaete Dinophilus gyrociliatus to chromium exposure.

The effects of chromium on the life history and demography of Dinophilus gyrociliatus (Polychaeta) were studied on a control and three treated cohorts kept in artificial seawater enriched with nominal concentrations of chromium at 1.0, 1.4, and 1.6 microg/ml. Survival and fecundity were significantly reduced by chromium. Fecundity was higher in the chromium treatments than in the control group at the beginning of the reproductive period; however, overall, the highest fecundity was observed in the control. Life expectancy, net growth rate, and generation time were also significantly reduced by chromium. The population growth rate (lambda) was higher in the treated animals than in the controls. The differences in lambda between the treated animals and the controls (deltalambda) were almost completely due to the differences in the life tables observed during the first three weeks of life. The differences in survival between the treated and control animals did not contribute to deltalambda. The contribution to deltalambda of the slight increase in age-specific fecundity in the early reproductive events compensated for the marked decrease in overall fecundity in the treated animals. The complex effects of chromium enrichment on D. gyrociliatus underline the importance of analyzing both individual and population responses when assessing the effects of pollutants on organisms. Our results confirm that D. gyrociliatus might serve as an indicator species in confined areas of polluted seawater such as lagoons and harbors.

Age Factors↗
PubMed1984

Laboratory observations on Toxorhynchites splendens Wiedemann in Thailand.

The biology of Toxorhynchites splendens predaceous larvae which breed in domestic containers like Aedes aegypti was studied. Egg stage lasts 52.64 +/- 0.13 hours. There are four larval instars lasting 2.38 +/- 0.04, 1.24 +/- 0.26, 8.09 +/- 1.6 and 28.78 +/- 5.39 days respectively. Pupal development lasts 5.18 +/- 1.06 days. The adult life span is 29.55 +/- 8.06 days. Growth increment was by measuring the size of head capsule. Number of second instar prey larvae consumed by 1 to 4 instars predaceous larvae were 9.32 +/- 1.77, 5.94 +/- 1.11, 37.03 +/- 7.05 and 273.06 +/- 50.69 respectively. The fourth instar was very aggressive especially 2-3 days before pupation when it killed without eating them. The construction of biological life table indicated net reproductive of increase (R0) of 16.3, capacity for increase (rc) of 0.094, finite rate of increase (lambda) of 1.08 and mean duration of a generation (Tc) of 44.445 days. The mortality at the first and second larval instar was high and the calculated population index (I) was 14.81.

Aedes↗
PubMedDate not supplied

Inbreeding and fertility in a South Indian population.

Among 1913 women in Karnataka State, South India, 37.74% had married a relative (a consanguineous union), 60.79% were non-consanguineously married, and 1.46% did not know whether they had married a relative. Mean number of living offspring for consanguineously married women who had completed their reproduction was 3.89, and for the non-consanguineous 4.07. There is no significant difference in the mean level of fertility for the two groups measured in this way. Pre-natal mortality is lower (but not significantly) among consanguineously married women who have completed their reproduction than among the non-consanguineous group, but post-natal mortality is significantly higher among the conceptuses of the consanguineously married women. Although consanguineously married women conceive more frequently, that is, are more fecund than the non-consanguineous women (mean number of conceptions being 6.61 and 6.28, respectively), the difference is not significant. The differential survival of the offspring results in the consanguineous group having slightly lower net fertility, although the difference is not statistically significant. The lower sterility rates of the consanguineously married women (3.21% of all consanguineously married women show primary sterility compared to 3.47% of the non-consanguineous) may be due to greater compatibility of uniting gametes in the consanguineous marriages. The data reveal that women married to a relative and having completed their reproduction show higher fecundity, lower pre-natal mortality, higher post-natal mortality, lower sterility rates, and thus no significant difference in net fertility to those who had not married a relative.

Adolescent↗
PubMed2005

Sexual conflict in the wild: elevated mating rate reduces female lifetime reproductive success.

Sexual conflict over mating rate is suggested to play a pivotal role in male-female coevolution, and females are predicted to reject superfluous mating attempts. Recent work suggests that direct effects of multiple mating on female fitness are not fully understood. A major concern in studies of sexual conflict is how well the data obtained under controlled laboratory settings relate to natural conditions. We tested the effect of female multiple mating on reproductive success in a natural population of a polyandrous spider, Stegodyphus lineatus. Previous studies show that a male who succeeds in entering a female nest also mates with her; therefore, we used male encounter rate as a proxy of female mating rate. We further elevated female mating rate by introducing males into females' nests. Female lifetime reproductive success was assessed as the likelihood of successful reproduction, offspring production, and juvenile offspring body mass. Increased mating rate increased the time to oviposition and reduced the likelihood of successful reproduction. Female mating rate negatively affected offspring body mass. Manipulated females produced fewer offspring than control females. The observed patterns imply a net cost of polyandry to females and suggest that natural mating rates can be suboptimal for females under natural conditions.

Animals↗
PubMed2005

Fertility in South Australian commercial Merino flocks: sources of reproductive wastage.

To identify reasons for low fertility in the Merino in South Australia, we defined the extent and sources of reproductive wastage in flocks of maiden (n=14) and mature age (n=54) Merino ewes managed on 43 properties over 4 year. In a second study, reproductive wastage was examined in a very high ovulating flock of mature age South Australian Merino ewes heterozygous for the FecB gene, mated to lamb in either the autumn or spring. Losses in the latter flock were examined in less detail than the large-scale study, but allowed wastage to be partitioned between pre- and peri/post-natal sources. In the first experiment, reproductive wastage between mating and weaning was estimated at 59.7 potential lambs or ova lost per 100 ewes exposed to rams, representing 42.4% of ova shed. The main source of wastage occurred at lambing (55.6% of total loss), with death of twins a major contributor (35.3% of total loss). Other important sources of wastage were from partial failure of multiple ovulation (PFMO; 20.4% of total loss) and from ewes mating but not lambing (13.2% of total loss). Reproductive wastage did not vary with either age of ewe (maiden versus mature) or season of mating (October-December versus January-March). Mean ovulation rate, estimated as 141 per 100 ewes ovulating (range 100-200), varied with age of ewe (129 versus 144; maiden versus mature) but not with season of mating or year (1990-1991). Values for fertility, fecundity and lamb survival were 90, 127 and 73%, respectively. Fecundity of maiden ewes was lower than that of mature ewes (116 versus 130). Survival of single and twin lambs between birth and tail docking was 83 and 56%, respectively. Net reproductive efficiency, or lambs weaned per 100 ewes exposed to rams, averaged 81 (range 31-122). In the second experiment, mean ovulation rate of FecB Merino ewes was 316 per 100 ewes ovulating, with 242 ova (potential lambs) lost between ovulation and tail docking. This loss was equally shared between pre- and peri/post-natal sources (123 versus 119), and demonstrates severe limitation of the Merino to successfully bear and rear multiple litters. We concluded that future research in commercial Merino flocks be focused on lamb mortality, particularly of twins, and on PFMO, the major source of embryo loss.

Aging↗
PubMed2006

Two distinct groups of natural populations of Fagopyrum urophyllum (Bur. et Franch.) Gross revealed by the nucleotide sequence of a noncoding region in chloroplast DNA.

Fagopyrum urophyllum is a cross-pollinating perennial woody shrub species belonging to the urophyllum group of Fagopyrum. Natural populations of F. urophyllum were morphologically classified into two distinct groups, the Dali group and the Kunming group without exception. This grouping was verified by molecular phylogeny based on the nucleotide sequence of chloroplast DNA. The reproductive isolation found between the two groups was almost perfect as the distribution of two groups did not overlap each other. The net nucleotide substitution rate (Da) between the two groups was at the same level as between two distinct species. These data suggests that the two groups should be classified into distinct species if future studies on F. urophyllum confirm complete reproductive isolation and no ambiguously classified populations in the border area of the central Yunnan province of China.

DNA, Chloroplast↗
PubMed2001

Alterations of physiological energetics, growth and reproduction of Daphnia magna under toxicant stress.

The study investigates the relationship between changes in physiological energetics of organisms and alterations of growth, development and reproduction of Daphnia magna. Groups of primiparous daphnids were subjected to 8-day exposures to the heavy metals cadmium and copper or to the cationic surfactant, cetyltrimethylammonium bromide (CTAB). Energetic alterations were estimated from the measurement of oxygen consumption and feeding activity which was performed during the last 3 days of the exposure period and from the calculation of simplified carbon balances. The physiological effects were compared to effects on organismal growth and reproduction as obtained from 17-day exposure experiments. Toxicant exposure reduced weight and body length of daphnids indicating an impaired growth rate, but effects on total metabolic costs measured as weight-specific oxygen consumption could not be detected. Net carbon gain of individuals decreased in a concentration-dependent way for the tested chemicals reflecting effects on biomass of daphnids. In the case of cadmium and copper, reproduction ( summation operatormx: number of offspring per female of age x born during the time interval x-1 to x, summarised over the entire exposure period) and the estimate for the intrinsic rate of natural increase, derived from the 17-day exposure-experiment, were affected at concentrations comparable to the effect levels as observed for growth. In the case of copper, the concentrations affecting growth and reproduction were close to the 17-day LC(50) value. CTAB caused a reduction in body length of primiparous daphnids whereas a decrease in the reproductive performance was not apparent. In conclusion, the chemicals did not change metabolic costs of exposed daphnids as it would be expected as a consequence of resistance or repair mechanisms, however, they induced alterations of SFG, growth, reproduction and intrinsic rate of natural increase. These alterations were chemical-specific. The fact that toxicant-related effects on growth and reproduction could not be linked to an elevated metabolic rate of daphnids may indicate that demand side effects occurred early during exposure - before the start of respirometric measurements - or that effects on growth were caused by an altered energy uptake. The results illustrate the importance of trade-off processes in regulating the distribution of energy among growth and reproduction of daphnids.

Animals↗
PubMed1991

Use of a simulation model to evaluate the influence of reproductive performance and management decisions on net income in beef production.

A stochastic dynamic model of reproduction and a deterministic cow-herd economic simulation model were used to evaluate how management decisions and reproductive performance interact to influence net income in a cow-calf operation (1,000 cows) for 1 yr of production. The stochastic model was used to determine herd performance when length of breeding season (45, 70, or 120 d) interacted with three postpartum intervals of anestrus (48, 65, or 90 d) and three conception rates at first service (60, 70, or 80%). Short, moderate, and long postpartum intervals were used to reflect differences in reproductive performance. In addition, replacement heifers were bred beginning either 3 wk ahead of the cow herd or at the same time as the cow herd. Fifty-four simulations were generated. Inputs into the economic model were herd performance, livestock and feed prices, nonfeed costs, and feed requirements for 1 yr of production. Feed requirements were calculated separately for each postpartum interval to reflect three different body condition scores, thin, moderate, and good, to correspond with long, moderate, and short postpartum intervals. Net income was greatest with 70-d breeding seasons when the postpartum interval was short or moderate. When the postpartum interval was long, net income was greatest with 120-d breeding seasons because pregnancy rates, as a result of the long breeding season, were highest and feed costs were lowest for thin cows. Overall, net income was greatest when cows were managed to have postpartum intervals of moderate length. Breeding heifers 3 wk before the cows provided the most economic benefit with long postpartum intervals.

Age Factors↗
PubMed1992

Onset of and recovery from nitrogen stress during reproductive growth of soybean.

Photosynthetic rates and allocation of dry matter, nitrogen, and nonstructural carbohydrates were determined during onset of and recovery from a nitrogen stress for reproductive soybean (Glycine max [L.] Merrill cv Ransom) plants. Until the beginning of seed fill, non-nodulated plants were grown in flowing solution culture with 1.0 mM NO3- in a complete nutrient solution. One set of plants then was transferred to minus-nitrogen solution for 24 d of seed fill; a second set was transferred to a minus-nitrogen solution for 14 d followed by return to the complete solution with 1.0 mM NO3- for the remaining 10 d of seed fill; and a third set was continued on the complete solution. Net CO2 exchange rates of individual leaves, which remained nearly constant during seed fill for nonstressed plants, declined at an accelerated rate during onset of nitrogen stress as the specific content of reduced nitrogen in the leaves was decreased by remobilization of nitrogen to support pod growth. The rate of nitrogen remobilization out of leaves initially was relatively greater than the decrease in photosynthetic rate. While rate of pod growth declined in response to the developing nitrogen stress, photosynthetic assimilation of carbon exceeded reproductive demand and nonstructural carbohydrates accumulated within tissues. Following resupply of exogenous NO3-, specific rate of NO3- uptake by roots was enhanced relative to nonstressed plants. While there was little increase in content of reduced nitrogen in leaves, net remobilization of nitrogen out of leaves ceased, and the decline in photosynthetic rate stabilized at about 51% of that for nonstressed plants. This level of photosynthesis, combined with the availability of elevated pools of carbohydrates accumulated during stress, was sufficient to support the increases in both the specific rates of NO3- uptake and the rate of pod growth during recovery.

Carbohydrate Metabolism↗
PubMed2000

Optimizing breeding decisions for Finnish dairy herds.

The purpose of this study was to determine the effect of reproductive performance on profitability and optimal breeding decisions for Finnish dairy herds. We used a dynamic programming model to optimize dairy cow insemination and replacement decisions. This optimization model maximizes the expected net revenues from a given cow and her replacements over a decision horizon. Input values and prices reflecting the situation in 1998 in Finland were used in the study. Reproductive performance was reflected in the model by overall pregnancy rate, which was a function of heat detection and conception rate. Seasonality was included in conception rate. The base run had a pregnancy rate of 0.49 (both heat detection and conception rate of 0.7). Different scenarios were modeled by changing levels of conception rate, heat detection, and seasonality in fertility. Reproductive performance had a considerable impact on profitability of a herd; good heat detection and conception rates provided an opportunity for management control. When heat detection rate decreased from 0.7 to 0.5, and everything else was held constant, net revenues decreased approximately 2.6%. If the conception rate also decreased to 0.5 (resulting in a pregnancy rate of 0.25), net revenues were approximately 5% lower than with a pregnancy rate of 0.49. With lower fertility, replacement percentage was higher and the financial losses were mainly from higher replacement costs. Under Finnish conditions, it is not optimal to start breeding cows calving in spring and early summer immediately after the voluntary waiting period. Instead, it is preferable to allow the calving interval to lengthen for these cows so that their next calving is in the fall. However, cows calving in the fall should be bred immediately after the voluntary waiting period. Across all scenarios, optimal solutions predicted most calvings should occur in fall and the most profitable time to bring a replacement heifer into a herd was in the fall. It was economically justifiable to keep breeding high producing cows longer than low producing cows.

Animal Husbandry↗
PubMed2005

Diel changes in the CO2 exchange rates of reproductive organs of the tropical tree Durio zibethinus.

The daily variations in the in situ CO(2) exchange of the reproductive organs of Durio zibethinus trees, growing in an experimental field at University Putra Malaysia (UPM), were examined at different growth stages. Reproductive organs emerged on the leafless portions of branches inside the crown. The photon flux densities (PFD) in the chambers used for the measurements were less than 100 mumol m(-2) s(-1) and were 40% of the PFD outside of the crown. The daytime net respiration rate and the nighttime dark respiration rate were higher at the time of flower initiation and during the mixed stages, when flower buds, flowers, and fruit coexist, than at the flower bud stage. The net respiration rate was lower than the daytime dark respiration rate at given temperatures, especially at the flower bud and fruit stages. Conversely, the net respiration rate was similar to the daytime dark respiration rate at the mixed stage. Photosynthetic CO(2) refixation reduced the daily respiratory loss by 17, 5, 0.3, and 24% at the flower bud, flower initiation, mixed, and fruit stages, respectively.

Bombacaceae↗
PubMed1991

Generation replacement in Europe since 1900.

The author examines population dynamics in Western Europe during the twentieth century, with a focus on changes in generations' ability to reproduce themselves. He applies "the concept of 'generation replacement', based on 'net' fertility, [taking] into account the mortality rates to which a generation of mothers is subjected up to the end of reproductive life. The conditions in which replacement occurs are measured by the reproduction rate, or replacement rate, which expresses the number of daughters by which each of the women born [in] a given year will, on average, be succeeded. Replacement is ensured when the rate is higher than one. To reach this level, the generation's fertility must be all the higher as mortality conditions are unfavourable."

Demography↗