Differences In Population Size Research Articles

Regulation of ovulation number in mammals. A follicle interaction law that controls maturation

The assumption that developing follicles communicate through circulating hormones has been used to obtain a class of interaction laws that describe follicle growth. A specific member of this class has been shown to control ovulation number. Although all interacting follicles obey the same growth law and are given initial maturities that are chosen at random from a uniform distribution, ovulatory and atretic follicles emerge. Changing the parameters in the growth law can alter the most probable ovulation number values, anovulatory states are also admitted as possible solutions of the growth law. The behavior of the model is examined for interacting follicle populations of different size. Methods are suggested for identifying growth laws in particular mammals. These can be used to test the model from experimental data.

Crohn's disease in Wales, 1967-1976; an epidemiological survey based on hospital admissions.

One thousand and ninety-eight patients from Wales were treated in hospital for Crohn's disease between 1967 and 1976, which gave an overall 'period prevalence' for the disease of 40 cases/10(5) of the total population. The data were analysed for each of the 8 counties and for rural as well as urban populations of different sizes. The disease was significantly more common in the urban counties of Gwent and the 3 parts of Glamorgan compared with the remainder of Wales. The highest prevalence was in South Glamorgan (54 cases/10(5)) and the lowest in Dyfed (30/10(5)). There was a relatively small but highly significant difference in the prevalence for urban populations larger than 10 000 (47/10(5)) compared with smaller communities which were chiefly rural (34/10(5)).

Standardized perinatal mortality ratios: technique, utility and interpretation

The utility and validity of perinatal mortality rates (PNMR) as indicators of the quality of health care services are analysed. A major determinant of the PNMR is the birthweight distribution, and this may be determined in a large part through social factors rather than health care services. A means of standardizing the PNMR according to birthweight, in the same way that an SMR is standardized according to the age and sex distribution of a population, is proposed and demonstrated. The particular advantages and problems arising from the use of the method are presented. Means of further improvement are identified. The perinatal mortality rate (PNMR) is widely used as an indicator of the quality of obstetric and early neonatal care. Thus, the Court Committee1 based several of its conclusions upon the PNMR, making comparisons between different parts of the United Kingdom and between this and other countries. Unfortunately, usage of the PNMR fails to discriminate obstetric and paediatric factors on the one hand and socioeconomic factors on the other. Among other effects, the latter strongly influence the proportion of premature infants, which in turn strongly influences the stillbirth and neonatal death rates.2 In view of the caution with which other crude mortality data are generally treated both by clinicians and epidemiologists, it is perhaps surprising how often circumspection is discarded when the PNMR is considered. In its crude form it is less than incisive and fails to provide the medical officer, obstetrician or paediatrician with a tool capable of providing unambiguous comment about the quality of the health care services in his own area, or his own maternity hospital. To serve this purpose it would be necessary to exclude from it, so far as is possible, the main social, that is, non-service, effects. Our aim in the present study is to investigate the use of indirect standardization methods to provide a standardized perinatal mortality ratio (SPNMR), analogous with the standardized mortality ratio (SMR), except that the standardization is carried out according to the birthweight distribution instead of in terms of age and sex. We shall examine a number of technical issues relating to the reliability of the available data and the statistical stability of the SPNMR for populations of different sizes. In particular, we shall investigate the extent to which successive years must be aggregated in order to give sufficient numbers. This is especially relevant as the size of the studied geographical area is reduced, and as particular subsets of perinatal mortality are isolated for separate examination. We shall inquire also into the need, at these levels, for additional standardization procedures.

The computer analysis of volume distribution curves. Demonstration of two erythrocyte populations of different size in the young guinea pig and analysis of the mechanism of immune lysis of cells by antibody and complement.

Guinea pig, rat and sheep erythrocytes were sized electrically using the hydrodynamic focusing technique. The experimental curves were approximated with a computer by linear and logarithmic normal distributions. Rat and guinea pig erythrocytes from adult animals were best approximated by one linear normal distribution. Two populations (I, II) of erythrocytes with different mean volume could be demonstrated in young guinea pigs by this analysis. Population I erythrocytes are small, have a lower electrophoretic mobility and are mainly present at birth. They are gradually replaced by the larger population II erythrocytes. Both types of erythrocytes are probably the result of separate differentiation pathways. The analysis of erythrocyte volume distribution curves during immune lysis by antibody and complement shows that intact and ghost erythrocytes are measured by electrical sizing. No volume changes were observed up to the EAC1-8 intermediate. After the addition of C9, a C9 dose-dependent part of the erythrocytes swell permanently to spheroids. The spheroid transformation is a temperature-dependent, all or nothing reaction which is independent of protein osmotic forces from the interior of the cell.

The hitch-hiking effect of a favourable gene

SummaryWhen a selectively favourable gene substitution occurs in a population, changes in gene frequencies will occur at closely linked loci. In the case of a neutral polymorphism, average heterozygosity will be reduced to an extent which varies with distance from the substituted locus. The aggregate effect of substitution on neutral polymorphism is estimated; in populations of total size 106 or more (and perhaps of 104 or more), this effect will be more important than that of random fixation. This may explain why the extent of polymorphism in natural populations does not vary as much as one would expect from a consideration of the equilibrium between mutation and random fixation in populations of different sizes. For a selectively maintained polymorphism at a linked locus, this process will only be important in the long run if it leads to complete fixation. If the selective coefficients at the linked locus are small compared to those at the substituted locus, it is shown that the probability of complete fixation at the linked locus is approximately exp (− Nc), where c is the recombinant fraction and N the population size. It follows that in a large population a selective substitution can occur in a cistron without eliminating a selectively maintained polymorphism in the same cistron.

Protein variation in the eye lens nucleus of the mackerel scad ( Decapterus pinnulatus)

1. 1. Electrophoretic patterns were prepared from mackerel scad ( Decapterus pinnulatus) nuclear eye lens protein extracted in 0·018 g% NaCl solution. 2. 2. Sixteen fish from Hawaii and sixteen from Kauai, islands 300 miles apart, produced two protein patterns in common. Kauai fish produced two additional patterns, suggesting separate breeding populations of different sizes. 3. 3. The uniformity of many patterns demonstrates the reliability of the electrophoretic procedure and the genetic basis of the patterns. 4. 4. Low molecular weight nuclear lens proteins vary intraspecifically, permitting identification of separate breeding populations. High molecular weight proteins are less variable; consequently, they should be particularly useful in systematics research.

The relationship between aphid infestations and oviposition by aphidophagous Syrphidae (Diptera)

SUMMARYOviposition by aphidophagous Syrphidae varies with the size of aphid infestations and different syrphid species have different optimum aphid population sizes for oviposition.In one experiment using potted brussels sprout plants infested with Brevicoryne brassicae L., Platycheirus manicatus (Meig.) preferred about 100 aphids per plant, P. scutatus (Meig.) about 1000 aphids per plant and Syrphus ribesii (L.) about 2000 aphids per plant. These preferences were less clear in certain Platycheirus species (e.g. P. peltatus (Meig.)), than in Syrphus species (e.g. S. luniger Meig.).Once a plant has been selected for oviposition there may still be selection of suitable colonies on that plant. For a given aphid population, S. luniger preferred a small number of large aggregates to a larger number of smaller ones, whereas S. balteatus (Deg.) preferred the opposite.The tendency of the different species to select aphid populations of different sizes and distributions is likely to decrease interspecific competition.

Size Distributions of Sedimentary Populations

Separate sedimentary populations are not all characterized by lognormal size distributions. Populations of different sizes of material are produced by different mechanisms of abrasion: pebbles and gravel by singlestage crushing; sand by repeated abrasion; and silt and clay by chipping from larger grains. Each mechanism imposes a different size distribution on the product.

The Edge Effect in Population Genetics

Many animal species have been observed in which populations living near the edge of the range differ from those more centrally placed. Sometimes different peripheral populations resemble each other more closely than they do the central ones. Such a distribution must be due either to more rapid change in central than in peripheral localities, or vice versa. In discussion of particular instances each alternative has its adherents. It is suggested here that in two examples from the European fauna (bank voles of the genus Clethrionomys and the snail Cepaea nemoralis) the distinct edge populations are less likely to be relicts than recent developments. Consideration of the response of populations of different sizes and breeding structure to the environmental conditions in various parts of the range suggests that we shall not know whether this is usually so, or whether peripheral populations play an important part in evolution, until the effects of coadaptation and interpopulation migration are better understood.

A New Measure of Dispersion

The measures of dispersion in common use are: (1) the standard deviation; (2) average deviation; (3) quartile deviation; and (4) the range. It is generally admitted that the merit of the range as a meas? ure of dispersion lies in its simplicity of determination and interpre? tation. To calculate its probable error has not been attempted; but were this done it would have little significance, for the range itself is not a constant function of a distribution, since, in general, it increases with an increase in population. The range is therefore unsatisfactory as a measure of dispersion, because it undoubtedly has a large probable error, and also because its significance varies as populations of different sizes are being considered. The probable errors of the other three measures are given in the sec? ond column of the accompanying table. The values in columns 2 and 3 must be multiplied by the standard deviation of the distribution, and the values in columns 2_and 4 must be divided by the square root of the number of cases (Vn) before they will serve in any particular prob? lem. For purposes of comparison of different measures, these factors are here omitted.