Life Table Data Research Articles

Some factors regulating cohort production of the crayfish, Orconectes virilis

SUMMARY. Cohort production of the crayfish. Orconectes virilis, ranged from 148.8 to 70.2 kg in North Twin Lake (surface area 1.9 ha) and from 151.9 to 84.9 kg in West Lost Lake (surface area 1.4 ha). Both cohort production (P) and cohort mean biomass (B) showed a long‐term decrease with time. The cohort P/B ratios did not show such a trend but remained steady. The P/B ratio approximated the life cycle instantaneous rate of growth (G) which could then be used for estimating cohort production from mean biomass.Production remained consistently higher in West Lost Lake. Analysis of horizontal life table data revealed no inherent difference between survival and fecundity rates of the crayfish population in each lake. Slight differences in basin morphometry between the two lakes determined nursery habitat availability and this affected recruitment of young from each female brood stock. Small differences in carrying capacity between two similar sized nearby lakes, along with a decrease in carrying capacity over time, were sufficient to nullify attempts to manage these populations using a maximum sustainable yield model.

Calculation of the Intrinsic Rate of Natural Increase, rm, With Rhabditis Marina Bastian 1865 (Nematoda)

The life-cycle of Rhabditis marina Bastian 1865 was studied at 25°C and 20‰ salinity. The following demographic parameters were computed from life-table data: the intrinsic rate of natural increase (r m ) = 0.914 day; net reproductivity (R o ) = 400; minimum generation time (T min ) = 4.5 days; cohort generation time (T c ) = 7.2 days; mean generation time (T) = 6.6 days; and the age of an adult female when a median egg is deposited (T) = 6.1 days. Several approximate equations used to estimate r m were compared with these life-table calculations. Some give erroneous estimations and should be used with extreme caution. For iteroparous organisms (including most free-living nematodes), T min only gives an indication of the development time and is therefore unsuitable for describing 'mean generation time'.

Age-specific life-table data for the Eucalyptus boring beetle, Phoracantha semipunctata (F.) (Coleoptera: Cerambycidae), in Malawi

AbstractAge-specific life-table data were collected over a year for field and insectary populations of Phoracantha semipunctata (F.) on logs of Eucalyptus grandis in Malawi. Most mortality occurred in the larval stage, and the major mortality factor was intraspecific competition. Severe overcrowding led to a reduction in population density from one generation to the next. Overcrowding also led to a reduction in beetle size and to a shift in the sex ratio in favour of males. Elimination of potential breeding sites is recommended as an effective control measure for this pest.

Predators and parasites of temporary row crop pests: Agents of irreplaceable mortality or scavengers acting prior to other mortality factors?

A study was conducted with the cabbage looper,Trichoplusia ni (Hubner), to determine: 1) whether naturally occurring entomophagous arthropods impart irreplaceable mortality to the cabbage looper in celery, and 2) whether entomophagous arthropods are present to impart such mortality toT. ni eggs and 1st instar larvae when the crop is sensitive to the pest. Predator evaluation involved 1) insecticidal + cage exclusion, 2) insecticidal exclusion alone, 3) D-vac removal of predators, and 4) sticky barrier exclusion. In all the exclusion regimes survival of eggs and larvae was higher than in the unexcluded control. Analysis of life table data was consistent with the hypothesis that some mortality of eggs due to parasitism byTrichogramma and of medium-larvae by other hymenopterous parasites was not replaceable by other mortality factors. The time of appearance of the first marketable petiole was correlated with both the height of the tallest petiole and the number of petioles on the plant. Peak densities ofTrichogramma and important predators occurred before the first marketable petiole appeared and declined to low levels as harvest approached.

A demographic study of the life cycle of Tisbe furcata (Baird, 1837) (Copepoda: Harpacticoida)

The life-cycle of the harpacticoid copepod Tisbe furcata (Baird, 1837) at 18 C was studied quantitatively. Stage durations were determined by two different methods, using synchronous cohorts. Combined nauplius stages last for 80·4 h; the successive copepodite stages take 23·0, 23·2, 28·0 (♀) to 23·2 (♂), 33·4 (♀) to 24·2 (♂) and 48·8 (♀) to 34·7 (♂) h, respectively. Females develop more slowly but more synchronously than males. Age-specific survival and fertility rates were used to calculate the stable stage distribution in an exponentially growing population. From life-table data the following demographic parameters were computed: intrinsic rate of natural increase rm = 0·233 day−1; net reproductive rate Ro = 94; minimum generation time Tmin = 14·9 days; parameters related to ‘generation time’: T = 19·5 days, = 16·4 days, Tc = 25·4 days.

Population dynamics of the swallowtail butterfly, Papilio xuthus L., in a deforested area

SummaryThe long‐term population dynamics of the swallowtail butterfly, Papilio xuthus, were studied by means of life table analysis in a deforested area, where the host tree, Zanthoxylum ailanthoides, was growing. The number of eggs laid on host trees in the deforested area decreases as secondary succession progresses. When the trees were classified into three groups, i. e. tall, medium and short, according to their height relative to the surrounding vegetation, less eggs were laid on tall than on short host trees. Life tables for the natural populations in each generation were developed on the basis of mean values for 6 years. Eggs and larvae in early stages were attacked chiefly by small‐ and middle‐sized predators, such as ants, spiders, bugs and orthopterids, while later stage larvae were attacked chiefly by birds or Polistes wasps. An inchneumonid wasp was the most important mortality factor in the pupal stage. Key‐factor analysis was tested on the life table data of each immature stage. The late larval stage was a key stage, and most mortality factors were considered to operate independently. The test for density dependency did not show any tendencies. The analysis of variance in two‐way classifications was carried out for the difference of survival rate among the tree groups. It was suggested that tall host trees were unsuitable for P. xuthus. The construction of life tables for artificially inoculated populations on large host trees showed that high physiological death rate were characteristic of such trees in comparison with natural populations on smaller trees. The characteristics of the population dynamics of P. xuthus in the deforested area are compared among some kinds of the habitat, and the interrelationship between P. xuthus and its host plant are discussed.

Late effects of whole or partial body x-irradiation on mice: life shortening.

Life table data were obtained on 2400 ddY/SLC female mice exposed at 10 weeks of age to a single dose of X-rays. Doses given to the whole body were 95, 190, 380 and 570 rad, and to head, trunk or lower body, 190, 380, 570 and 760 rad. The mean survival time of unirradiated controls was 73 weeks. The mean survival times after whole body exposure decreased linearly with increasing dose. The estimate of life shortening per 100 rad was 7.2 per cent for whole body exposure. The life shortening after head or lower body exposure to a dose of 190 rad was 6.2 and 7.1 weeks respectively, and almost no further life shortening up to 760 rad. After trunk irradiation with 190 rad, life shortening was 10.4 weeks and beyond that dose life shortening was 1.1 per cent per 100 rad.

An evolutionary model of female dominance relations in primates

Though a few authors have provided individual selection explanations for the existence of dominance hierarchies, no unitary functional model exists which is capable of accounting for specific forms of dominance hierarchies. The framework of a model of female dominance relations in primates is developed and should be applicable to other species exhibiting overlapping generations, iteroparity, low female dispersal, and high parental investment. This model is based on the principles of individual selection, kin selection, reproductive value, and evolutionarily stable strategies. Three functional hypothesis are presented concerning female dominance relations. These hypotheses are tested using life table data for Macaca mulatta. Sister-sister, mother-daughter, and other rank relations are analyzed in detail taking into account self interest, conflicts of interest, and the interest of supporters in rank relations. One of the hypothesis satisfactorily accounts for the principal elements of the female dominance hierarchy in Macaca mulatta.

Age Determination of the Blue WildebeestConnochaetes Taurinusin Zululand

Age determination methods for the blue wildebeest employed the use of tooth eruption sequence, cementum layers from macroscopic tooth sections, eye lens mass, and tooth attrition. Eleven eruption classes were arrived at, providing a reliable method of age determination up to 3,5 years. The times of eruption of specific teeth were compared with data from East Africa. The restricted birth interval of wildebeest enabled some sub-adult animals to be regarded as ‘known-age’ which were used to arrive at a value for the number of cementum layers laid down per annum, and to provide a ‘correction factor’ for the period before eruption and cemental deposition. The nature of tooth cementum lines in wildebeest is discussed, and changes in infundibular patterns were related to cementum or eruption age, providing an age-wear chart with 14 adult classes, adequate for life-table data. Incisiform wear in wildebeest appears to follow a curvilinear relationship. When eye lens mass was plotted against cementum or eruption age, the resultant curve served only to distinguish between animals below one year old and the older age classes. Anomalies in dentition are discussed. Some criteria for age determination in the field are presented.

Hyperthyroidism in the Land of Graves: Results of Treatment by Surgery, Radio-iodine and Carbimazole in 837 Cases

A review of the outcome of treatment by subtotal thyroidectomy, radio-iodine and carbimazole of 837 patients with hyperthyroidism seen consecutively over the period 1954--78 inclusive is presented. The age and sex distribution, the male to female ratio, the ABO blood group distribution and the prevalence of pernicious anaemia and diabetes mellitus in these patients was also analysed. Life-table data showed that the five-year and ten-year cumulative relapse rates following a two-year course of carbimazole (n = 162) were 56 per cent and 62 per cent; following surgery (n = 266), 6 per cent and 10 per cent and following radio-iodine (n = 43), 3 per cent and 14 per cent. Five-year and ten-year cumulative hypothyroid rates after surgery were 10 per cent and 18 per cent, and after radio-iodine 10 per cent and 30 per cent. Hypothyroidism did not occur after carbimazole therapy. Of 31 patients who took carbimazole for less than two years (mean 11 months, range 6--19 months), 91 per cent had relapsed at five years. Of 79 patients treated for longer than two years (mean 3.8 years, range 2 1/2--14 years), relapse rates at five and eight years were 49 per cent and 62 per cent. Nine patients (3.4 per cent) suffered permanent vocal cord paralysis and five (1.9 per cent) had permanent hypocalcaemia. The male/female ratio was 9.9 to 1, with a peak female prevalence between 25 and 30 years and a peak male prevalence between 40 and 45 years. The ABO blood group distribution among patients did not differ significantly from the distribution in the general population (chi 2 = 13.4, p = 0.2). Forty-seven patients (5.6 per cent) had diabetes mellitus and thyrotoxicosis whilst two patients (0.23 per cent) had diabetes, thyrotoxicosis and pernicious anaemia.

Predators of citrus blackfly [Hom.: Aleyrodidae

A 2-year survey of known whitefly predators was conducted from winter 1976 to winter 1978 in Broward County, Florida. Also, the impact of predators on citrus blackfly populations was measured under field conditions using lifetable data and predator exclusion data. In addition, feeding experiments were conducted to determine specific predators on different citrus blackfly stages.

Geographic Variation Among the Life Table Characteristics of Culex tritaeniorhynchus from Asia1

The adult horizontal life table characteristics of 9 strains of Culex tritaeniorhynchus Giles from 4 countries in Asia were compared under insectary conditions. Life expectancy ranged from 11.8 to 17.2 days for males and from 18.2 to 28.5 days for females. The net reproductive rate ranged from 14.4 to 98.5 living female offspring/female per generation, generation times ranged from 22.2 to 29.8 days, and the innate rate of increase, rm, ranged from 0.088 to 0.192. Although morphologically similar, the Japan strains were larger and among the longest lived, but generally oviposited fewer total egg rafts which were distributed throughout the female's life resulting in longer generation times and lower r m values than strains from Pakistan, Bangladesh, and Taiwan. The Taiwan strain, geographically nearest to the Japan strains, was similar to the subcontinent strains in life table attributes. Possible explanations for among strain differences are discussed in the context of ecological conditions at the locality of origin and insectary culture techniques. Interspecific comparisons with existing life table data for Aedes aegypti (L.) and Culex quinquefasciatus Say are presented.

Children's Experience of Marital Disruption

This paper uses life-table procedures and data from the 1973 Family Growth Survey to ask three basic question: (1) What is the cumulative probabilty that by a given age a child will have experienced a single-parent family as a consequence of marital dusruption? (2) Given a marital disruption, what is the cumulative proportion of children either experiencing parental remarriage or reaching age 18 within a given number of years following disruption? (3) What is the average duration of experience in a single-parent family? Estimates based on the early 1970s suggest that about one-third of all children will spend some time in a single-parent family before age 16 as a consequence of marital disruption (children born between marriages are included in these estimates, but those born before their mother's first marriage are not). There are very large differences by race, education, and the age of the mother at the child's birth. These differences appear in the timing as well as in the prevalence of marital disrup...

Comparing Observed Life Table Data with a Known Survival Curve in the Presence of Random Censorship

Summary A simple statistic is presented for comparing grouped survival data, which may be variably right censored, with a known survival curve. The known or hypothesized survival curve may be specified either analytically or in terms of a life table. This statistic has good power against local proportional hazard alternatives. The asymptotic distribution theory of the test is valid provided terms of order 00A3) in the actuarial interval lengths ^ are negligible. For comparison we give an actuarial modification of a statistic studied by Breslow (1977) which has the desired asymptotic distribution if terms of order 0052) are negligible. In the presence of intrainterval censorship, a statistic proposed by Oleinick and Mantel (1970) has the asserted asymptotic distribution only if terms of order Oft) are negligible. Thus the statistic we propose is preferable for coarsely grouped data. For short intervals with small death and censorship probabilities, the three statistics are numerically close.

The four-parameter logit life table system

Summary Brass's model life table system, which is a two parameter system based on the logit transformation of survivorship values, has been widely and successfully used to describe age patterns of mortality in many populations. As more reliable information has become available for populations with mortality patterns which differ in important ways from the assumed standard pattern of mortality, a more flexible model system is needed. This paper shows how Brass's system can be expanded into a four-parameter model, and evaluates the performance of the new system by examining how well it can fit observed life table data.

The Midsummer Dynamics of Two Daphnia Species in Wintergreen Lake, Michigan

During 1976, midsummer reductions in densities of Daphnia pulicaria and Daphnia galeata mendotae populations occurred in Wintergreen Lake, Michigan. Previous attempts to determine the causes of such declines have indicated correlations between predator populations, the presence of unpalatable algae or high midsummer water temperatures, and the reduction or disappearance of the daphnid populations. In this study, in situ life table experiments were performed to assess the influence of natural food and temperature conditions on population growth. A weekly sampling program showed that D. pulicaria was dielly concentrated, after early summer, at depths between the anaerobic hypolimnion and the warmer epilimnion, consistent with previous information indicating it to be a cold—water species. However, in situ life table data showed that D. pulicaria was capable of surviving in epilimnetic water up to 27°C, although reproduction was greatly reduced for a 6—day period in mid—July. This reduction in reproduction appeared to be the result of an interaction of high temperatures, declining standing crops of small algae and increasing amounts of Anabaena, Ceratium and Volvox. Daphnia galeata mendotae did not show any adverse response to these mid—July algae—temperature conditions. Analysis of predator gut contents suggested that both daphnids were heavily preyed upon by bluegills (Lepomis macrochirus). Shifts in the size structure of the daphnid populations were also consistent with intense size—selective predation by bluegills, as was the tendency for the age distribution of parthenogenic eggs to become skewed to younger eggs as the midsummer decline proceeded. Differences in body size, ephippial production and habitat preferences between the 2 species are also consistent with the hypothesis that planktivory is a strong selective force in their evolution.

How far does exposure to radiation mimic ageing in insects?—I. Life table data from the blowfly, Calliphora erythrocephala

Life table data have been obtained from populations of blowfly images ( Calliphora erythrocephala) following various exposures to γ-irradiation, in an attemp to discriminate between ‘precocious ageing’ (Baxter and Blair, 1967), ‘accelerated ageing’ (Lamb and Maynard Smith, 1969) and a ‘specific radiation syndrome’ (Atlan et al., 1969). The results do not support a ‘precocious’ theory of ageing, but fail to distinguish clearly between the other two interpretations; the reasons are discussed.

Reduction in fitness of the gastrotrichLepidodermella squammataby dilute acid mine water and amelioration of the effect by carbonates

Individuals from a clone of Lepidodermella squammata were cultured in lake water (control) and 6 solutions of dilute acid mine water with constant conductivity but varying carbonate content. Life table data were analysed based on a cohort of 45 animals for each treatment. Animals were able to survive briefly in dilute acid mine water (370/imho/cm total conductivity) with levels of carbonate below 12 ppm. At higher levels of carbonate, survival was similar to controls, and reproduction increased significantly with increasing carbonate level over the range tested, 13–67 ppm, with a plateau in the mid- range of 17–47 ppm. Mean number of eggs per female in the control and the 4 test solutions supporting reproduction was directly related to carbonate level, while variance was inversely related to carbonate level. Both environmental and genetic sources for the observed variability were minimized experimentally. Nevertheless, increased selection pressure, occurring in the presence of dilute acid mine water throu...

THE SELECTIVE ADVANTAGE OF FOUNDRESS ASSOCIATIONS IN POLISTES FUSCATUS (HYMENOPTERA: VESPIDAE): A FIELD STUDY OF THE EFFECTS OF PREDATION ON PRODUCTIVITY

AbstractColonies of P. fuscatus that were initiated by various numbers of foundresses were studied to gather basic life table information. This information was used to estimate the selective advantage of foundress association according to a kin selection model, a parental manipulation model, two individual selection models, and a combined kin and individual selection model. Life table data were obtained for colonies located in exposed nest sites and for colonies located in nest sites provided with protection from vertebrate predators. Relative productivity of colonies produced by different size foundress associations and under different levels of predation pressure were determined. Multiple foundress colonies were found to be more productive and have an increased ability to re-establish after an episode of predation when compared with single foundress colonies. When predation levels on the colonies were high, multiple foundress colonies were more productive per colony and per foundress. When predation levels on the colonies were low, multiple foundress colonies were more productive per colony but less productive per foundress. At high levels of predation, when the queens and joiners were all assumed to have equivalent potential productivities, the kin selection model, the parental manipulation model, and the combined kin and individual selection model all predicted a selective advantage for joiners in foundress associations. At low levels of predation, when the wasps are assumed to have equivalent productivities, only the parental manipulation model predicted a selective advantage for joiners in foundress associations. When the assumption of equivalent potential is relaxed and when the wasps are assumed to be capable of detecting and acting upon individual differences in productivity, then all of the models could account for the existence of foundress associations. However, under this last set of assumptions the individual selection models require that the joiners have very low potential productivities.

633 NEW PROGNOSTIC FACTORS IN CHILDHOOD LEUKEMIA (ALL)

Since Feb. 1975, 883 previously untreated children with ALL have been entered on a protocol designed to evaluate prognostic factors which influence induction, remission duration and survival and to identify subsets of patients with high risk of early failure. Complete marrow remission (M1) rates ranged between 91-95%. The combination of older age (>10yrs), high initial WBC (>20,000/μ1) and low serum IgG are associated with a significantly lower M1 rate. Skin test response to recall antigens, serum inhibition of blastogenesis, HLA type or PAS positivity were not prognostic of induction or remission duration. Patients in poor prognostic group (any age, initial WBC>50,000/μ1) with L1 blasts (FAB classification, Br.J.Hem 33:451,1976) had higher M1 rate than those with L2 blasts (80 vs 67%). Using the Mantel-Peto-Cox Chi square statistic for life table data, significant factors associated with poor prognosis include: WBC>20,000/μ1; age >7yrs; M3 marrow day 14; CNS disease at diagnosis; L2 lymphoblasts; decreased serum IgG and IgA; black race. Mediastinal mass is not an independent factor. None of 41 patients in low risk group (age 3-7yrs, WBC<10,000/μ1) with L1 blasts, M1 marrow on day 14, and normal Ig has sustained an adverse event (relapse or death). Identification of prognostic factors should permit more efficient and effective design of future protocols particularly for patients with good and poor prognosis.