A field study of the effect of prebaiting on censusing by the capture-recapture method in a vole population

Summary Populations of the vole,Clethrionomys rufocanus, in a lowland woodlot of Hokkaido were studied for the presence of effects of prebaiting on censusing by the capture-recapture method. A grid of 121 live-traps, spaced 5 m apart, was laid out on each of two plots, one of which alone was prebaited three days long. Owing to very high densities and great trap-efficiency, sufficient and favourable samples could be available for statistical analysis, except the trend of delayed catch for young in sampling. The population on either plot, however, proved to be markedly variable in catchability of unmarked animals in the course of trapping; while the probability of recapture was counted as invariable on the average from day to day, the recapture frequency was different between juveniles, subadults and adults. Needless to say, the catchability was distinctly greater for marked voles than for unmarked ones, whether prebaited or not, through the trapping period, except that the first-day catchability for unmarked ones on the prebaited plot seems not to be significantly lower than that for marked ones. Consequently, it turns out that the prebaiting has almost never helped to eliminate the important bias induced by differential trap-response of marked and unmarked animals; its contribution is only that the catchability for unmarked ones is slightly higher on the part of the prebaited plot on earlier days of the period. In accordance with the heterogeneous catchability, the Γ-form distribution analogous to the geometric could be applied with thorough fitness to the capture frequency in order to estimate the whole populations. The fact that the estimates are reliable, being not at any rate underestimates, was further confirmed by the result of a follow-up work conducted by means of the removal method with wider trap-spacing which brought forth distinct underestimation chiefly referable to unexposure to traps of the partial populations. The subject of unexposure was discussed by laying stress on the relation between minimum range length and trap-spacing. Contribution from JIBP-PT No. 88, carried out by the grant from the expenditure of Education Department to the specific study on “Dynamics of Biosphere”.     

Investigation into the edge effect by use of capture-recapture data in a vole population

Summary A substantial explication of the edge effect has been attempted by use of capture-recapture data for a vole population (Microtus montebelli), gathered intwo plots of 100×100 m or less during 12 days, cheked twice daily, in August 1970; the sample was quite sufficient for the aim. The edge effect as guessed by increased catch per trap is usually suspected to ensue from range-settlers in the outside boundary strip of a plot and immigrants. But by a theoretical analysis I could attain a tentative conclusion that no increased catch per trap will occur unless any invasion takes place. Then it follows that, apart from the effect of invasion, the role of the adjoining outside settlers in the edge effect is essentially required to be studied in the light of knowledge on the truth of size and shift in home range. The variation in range behavior for 183 adult voles, captured 6 times or more, could be grouped into eight types, of which the range-conservative type possessed 52% of the sample and the group of the type was justly utilized for giving averages of range size. Besides, it was seen from the observed frequency of types that a considerable number of immigrants onto the census plot were induced perhaps being allured by trap baits, but the majority of them proved to be assigned to the voles that have their ranges inside the assessment line ofDice; the rest referable to effective immigrants was only a few (7%). I could perceive no reason such as disproves the idea ofDice’s additional boundary strip. Viewed from maps of ingress shift of ranges, the effect of ingress must have been greater in the outer trap rows than in the inner within the plot, so that it might well be called edge effect in general; such effect, however, is seen gradually diminishing toward the center, and hence it is almost unlikely that one should find any clear-cut intra-plot assessment lines demarcating such an inner square as quite free from edge effects. Averages of observed range length and width (ORL and ORW), as reliable measures for the true range size, were determined from the above group of specimens; as a result, the remarkable concept of elliptic range shape was established by regarding ORL as long axis and ORW as short one, and, directly from these averages, the mean range sizes worked out at 0.04 for females and 0.09 for males in acreage which proved to be surprisingly well agreeable with those of isotope-revealed ranges for voles given byGodfrey (1954) andAmbrose (1969). The catchability for marked voles ( ) was estimated by the maximum likelihood method by use ofJolly’s formulae (1965), but that for unmarked ones ( ) was made by the regression census formula; as a result it was shown that the population was clearly of π>p type and that the trap-experience that voles underwent one month or more ago can make them retain as high catchability as π. Contribution from JIBP-PT No. 110, carried out by the grant from the expenditure of Education Department to the specific study on “Dynamics of Biosphere”.     

A possible discrepancy between the exposed and the whole population depending on range-size and trap-spacing in vole populations

Conclusion From a field study for the vole population (Clethrionomys rufocanus) in Hokkaido in the late summer of 1965, it has been proved that the range length may decrease from 25 to 18 m by the gross along with the rise from 20 to 100 in the density level per acre, and hence that an appreciable discrepancy, due to underestimation, may be produced in estimates of the exposed as compared to the whole population at an outbreaking density as high as 100 on a plan with trap-spacing 10 m. In consideration of this together with my preceding results, the strict terms that we may enough approximate the whole one by estimating the exposed seem likely to be that the ratio of range radius to trap spacing, supposing a range is circular, should be near 2 or more at either ordinary or outbreaking densities, to say in the concrete, that the trap spacing as close as 5 m or so in grid is desirable with this vole, perhaps with most other voles.     

New regression formula to estimate the whole population for recapture-addicted small mammals

Summary We have devised a census formula of curvilinear regression suitable for capture-recapture data of recapture-addicted populations of the Japanese field vole (Microtus montebelli) obtained under a grid-plan with single-catch traps in order to estimate the whole population. The equation is founded on the assumption that the trappable population on the initial day is increased in way of an exponential curve until it reaches to the whole during one trapping period. The effect of trap-preoccupation by marked and multiple collisions is considered in the formula. As a result of its application to field data of the vole, it has turned out that the equation is required for the data gained under the trapping plan with trap spacing 10m, but not for those under the plan with spacing 5m, to estimate the whole. A convenient method of analysis of the formula is offered here, but we have been yet unable to introduce assymptotic variance of estimates. Contributions from JIBP-PT No. 19, carried out by the grant from the expenditure of Education Department to the specific study on “Dynamics of Biosphere”.     

Regulation of reproduction rate in a cyclic population of the red-backed vole,Clethrionomys rufocanus bedfordiae

Summary Changes of the components of reproduction were analyzed quantitatively in a two-year cyclic population (which has two peaks in alternate years during a five-year census) of the red-backed vole,Clethrionomys rufocanus bedfordiae, with reference to its regulatory mechanism: (1) Variation in sex ratios was not associated with population phase or density, although a higher percentage of females in mature individuals was observed in the increase phase. (2) Females attained to sexual maturity at younger age and at lighter body weight than did males. All the youngest mature individuals were found in the low and the increase phases. Age and size at maturity became older and larger as the population went toward the peak phase. (3) Maturation rate was strongly associated with population phase and density; this component is an important and good parameter to predict population trend. Maturation rates were in the order, the low phase>the increase phase>the peak phase>the decline phase; the differences in the rates among these phases were significant. Maturation rate was somewhat depressed when the population density exceeded about 40 individuals/ha. Changes in age at maturity and in maturation rate are interpreted as derivative phenomena related to the population density and the capacity of the number of mature voles per unit area. (4) The maximum number of mature individuals were 26 males/ha and 29 females/ha; there was almost no increase of the number of mature voles at higher population densities over about 40 individuals/ha. The number of exclusive home ranges per hectare calculated from the observed range lengths did not differ much from the maximum number of mature voles of either sex. (5) Length of breeding period was shorter in the high-density years than in the low-density years; the breeding started earlier and ended earlier in the former than that in the latter. In the increase phase a few voles reproduced in winter. (6) The percentage of pregnant females was significantly lower in the peak phase than those in the other phases.     

对我国2010年人口普查事后调查工作的若干建议

人口普查不可能100％计数每一个人。世界上许多国家都在人口普查后组织事后调查,使用双系统估计量另行求得一个全国人口真实数的估计数,并以此为标准估计人口普查的净遗漏率。我国历次人口普查后都进行了事后调查,其主要缺陷是未对抽取的样本事后分层,未估计“全国真实的人口数”。建议我国2010年事后调查方案在克服这两个缺陷的基础上科学确定全国的样本总量。实行两步抽样等。     

人口普查工作新平台：人口地理信息系统

本文在回顾我国人口普查传统方法技术基础上 ,分析了新形势下国内外人口普查技术新进展 ,并指出人口地理信息系统的建设是我国人口普查新工作平台。本文探讨了人口地理信息系统基本功能和系统结构 ,并从五个方面详细分析人口地理信息系统如何辅助人口普查工作 :普查登记阶段 ,GIS技术可以辅助划分普查区域 ,绘制出普查地图和调查小区地图 ,提高速度和准确性 ,确保地域上的不重不漏 ;利用人口GIS ,可以充分发挥基本单位名录库在普查中的重要作用 ;利用人口GIS ,可以拓宽抽样调查和专项调查应用领域 ;利用调查小区空间不变性 ,可以统一普查资料空间基准 ,极大的拓宽普查资料应用范围 ;利用人口GIS ,可以加深人口普查数据的开发利用。未来十年内 ,将会有更多的区域建设各等级人口专题地理信息系统。     

Evaluation of statistical precision and design of efficient sampling for the population estimation based on frequency of occurrence

Summary The binomial sampling to estimate population density of an organism based simply upon the frequency of its occurrence among sampled quadrats is a labour-saving technique which is potentially useful for small animals like insects and has actually been applied occasionally to studies of their populations. The present study provides a theoretical basis for this convenient technique, which makes it statistically reliable and tolerable for consistent use in intensive as well as preliminary population censuses. Firs, the magnitude of sampling error in relation to sample size is formulated mathematically for the estimate to be obtained by this indirect method of census, using either of the two popular models relating frequency of occurrence (p) to mean density (m), i.e. the negative binomial model,p=1−(1+m/k) ^−k, and the empirical model,p=1−exp(−am ^b). Then, the equations to calculate sample size and census cost that are necessary to attain a given desired level of precision in the estimation are derived for both models. A notable feature of the relationship of necessary sample size (or census cost) to mean density in the frequency method, in constrast to that in the ordinary census, is that it shows a concave curve which tends to rise sharply not only towards lower but also towards higher levels of density. These theoretical results make it also possible to design sequential estimation procedures based on this convenient census technique, which may enable us with the least necessary cost to get a series of population estimates with the desired precision level. Examples are presented to explain how to apply these programs to acutal censuses in the field.     

Combining pheromone-baited and food-baited traps for insect pest control: Effects of additional control by parasitoids

Summary Two age-structured population dynamic models are analyzed in which pheromone-baited trapping and food-baited trapping are used simultaneously to eradicate an insect pest. The pest species is assumed to be under partial control by a host-specific parasitoid species. The two models assume that density-dependent population regulation is accomplished either by host larval competition or by means of oviposition interference among the parasitoids. The two trap types interact in a positive synergistic manner and this combination appears to be very promising as a useful combination of pest control methods. Several features of the system are examined; the feature which appears to cause the greatest problem is the possibility of the parasitoids being attracted to the pheromone or the food traps. In either case, the degree of attraction does not have to be very great to undermine the control effort. It is seen that food trapping becomes indispensible if host pheromone is used by the parasitoids as a host-locating kairomone. If odor in the food traps is used by the parasitoids as kairomone, then the situation appears more optimistic, as the reduction in efficiency of the food traps appears much less than with the pheromone traps when pheromone acts as kairomone.     

The effects and limits of territoriality on population regulation in grey red-backed voles,Clethrionomys rufocanus bedfordiae

Summary The effects of breeding territoriality on the stability of grey red-backed vole (Clethrionomys rufocanus bedfordiae) populations were investigated on a control grid and a grid on which the voles were fed, in an outdoor enclosure in Hokkaido, Japan. Vole populations were monitored by live trapping from 1984 to 1986: (1) Population density was 2–7 times greater on the experimental grid to which food was added than on the control grid. Reproductive output was more closely associated with the difference in density between grids than survival or dispersal (immigration and emigration) rates. (2) The number of adult females and pregnancy rate of the experimental population were significantly greater than those of the control one. The difference in the number of adult females between the populations was greater than that in pregnancy rate. (3) The proportion of successful litters and the number of weanlings per litter were not significantly different between the control and experimental population. (4) Adult females held territories on both the control and experimental grid; they were spaced out more than would be expected from random occupation. The territories overlapped more on the experimental grid than on the control grid. (5) Mean territory size of adult females on the experimental grid was about half of that on the control grid. The territory size was correlated negatively with population density. (6) The proportion of trap sites that were used by adult females was significantly greater on the experimental grid than on the control grid. This suggests that adult females on the experimental grid used the area more extensively. This factor, in association with territory size and overlapping of territory, was also important in causing the difference in the number of adult females between the grids. (7) These results call into question the hypothesis that territoriality stabilizes the density in populations ofClethrionomys.     

Assessing the validity of intercensal comparisons of indigenous Australians, 1986–96

The credibility of analysis of 1996 Census data on indigenous Australians hinges on who the people are who have changed their indigenous identification between the last two censuses. The number of people who identify as indigenous in either the Post-Enumeration Survey or the census is more stable than theprima facie evidence indicates. Also, the continuing low levels of education among the indigenous population means that self-identification signifies that one is, more than likely, disadvantaged. While it is difficult to say with absolute certainty that census statistics accurately reflect the economic status of the indigenous population, they are sufficiently credible to be taken at face value.     

Studies on the spatial distribution pattern of larvae of the mosquito,Anopheles sinensis, in rice fields

Summary The spatial distribution patterns of the population ofAnopheles sinensis larvae were studied in the rice field area in the suburb of Urawa city in Japan, during the summer seasons in 1973 and 1974. The distribution pattern of the larval population within the field, analysed by the m−m regression method, indicated that the basic component of larval distribution was not a group of individuals but a single individual and such components were distributed contagiously over the field. This basic pattern did not change significantly according to developmental stage, census date or field. Therefore, we could describe the distribution pattern of the population in a rice field by the single linear regression, x=0.021+1.339x(r²−0.912). Also, the relation for the whole population in the field area including the five fields could be shown by the linear regression, x=0.049+1.749x(r²−0.959). The value of α remained to be nearly equal to zero, but the value of β became larger than the value for the single-field relation. Such a change in distribution pattern seemed to reflect the greater heterogeneity in conditions among the fields than within individual field. Using the information on the distribution patterns mentioned above, some considerations were given on the sampling plans for mosquito larvae, including samplesize determination and application of sequential methods to estimate population size as well as to classify population level.     

Lifetime reproductive success in reproductively suppressed female voles

Summary A population of the grey red-backed vole,Clethrionomys rufocanus bedfordiae, was investigated on a 1 ha control grid and a 1 ha grid on which the voles were fed within a 2.1 ha outdoor enclosure in Hokkaido, Japan by live trapping from 1984 to 1986, for testing the Reproductive Suppression Model of Wasser and Barash (1983)-females can optimize their lifetime reproductive success by suppressing reproduction when future conditions for the survival of offspring are likely to be sufficiently better than present ones as to exceed the costs of the suppression itself. Age at the first pregnancy more varied in a higher density population on the experimental grid and females could be classified into the early and the late reproductive type in two generations (A: females born from February to June 1985; B: females born from September to November 1985). Lifetime reproductive success (the number of pregnancies, the number of successful litters, and the number of offspring) was not different between the early and the late reproducing females. The late reproducing females lived for longer periods than the early reproducing females, so that the loss by delayed start of reproduction was compensated for by a longer life span. Life span was not different between offspring of the early and the late reproducing females. These facts supported the Reproductive Suppression Model.     

The US Decennial Census: Political Questions,Scientific Answers

The US decennial census was initiated in 1790 to facilitate nation‐building tasks, especially that of reconfiguring political representation as the population grew and settled new territories. To this basic task of power distribution have been added other key governmental functions, such as the use of census data in guiding revenue sharing and in the enforcement of nondiscriminatory policies. Throughout its history the census has been the focus of partisan clashes. Following the identification of the “differential undercount” a measure of how census coverage differs across demographic groups and geographic areas–the partisan battles intensified, and in recent decades have come to focus not just on how the census counts are used but how the census data are collected. It has been argued that census methodology could be designed to predetermine given partisan outcomes, and for the 2000 census this charge shifted from “could be” to “is.” The Census Bureau has taken extraordinary steps to demonstrate that no partisan considerations have affected the design or implementation of the census, and that its decisions are based solely on the best technical judgment available.     

The use of sampling in conjunction with population censuses

In Asia and the Pacific, the practice of governments is increasingly to collect information on their populations' size, age and sex composition, geographic distribution, and certain other basic demographic and socioeconomic characteristics on the basis of a complete (100%) enumeration, and to supplement this basic information by collecting information on a larger range of variables on a sample basis. The additional information, which is gathered as part of the census operation, may be related to such population characteristics as migration, employment, fertility, and health. A complete census is generally indispensable for obtaining information about small domains, and also for obtaining politically important data, which must be seen to be free from sampling variability. A complete census is typically confined to obtaining a detailed picture of the number and basic structural characteristics of the entire population, with as much detail as possible about local areas. Sample surveys can quickly obtain a wider variety of more complex data. Sampling applications for the census include 1) using sampling in the design and control of census operations, such as in planning, testing, controlling, and evaluating the census; 2) using sample enumeration to supplement items covered in the complete census; 3) sampling the census results for processing to make the results available more quickly and at lower cost; and 4) extracting samples of microlevel files of detailed census data so as to facilitate dissemination of primary data.     

The Population of Centenarians in Brazil: Historical Estimates from 1900 to 2000

Since the nineteenth century, the census has provided the number of 100-year-olds in Brazil, one of the most populous countries worldwide. In 1900, 4,438 individuals reported themselves to be centenarians, a figure that increased about fivefold by the 2000 census. However, due to data quality issues, we are skeptical about the real size of the recorded population in the Brazilian census. We offer alternative estimates of the most likely number of centenarians during the twentieth century by combining variable-r relations with different mortality models. Our results indicate there was virtually no centenarian at the beginning of the twentieth century. The population has become larger than 1,000 individuals only in the 1990s, suggesting there has been an extensive, although diminishing, overenumeration of centenarians in the census records. Our results can help policymakers to plan the demands of a growing old age population in places that face stricter family and public budget constraints.     

The role of vole populations in prevalence of the parasite (Echinococcus multilocularis) in foxes

Effects of population fluctuation of the gray-sided vole(Clethrionomys rufocanus) on the prevalence (infection rates) of the parasiteEchinococcus multilocularis in red fox(Vulpes vulpes) populations was investigated from 1985 to 1992 in eastern Hokkaido (Abashiri, Nemuro, and Kushiro area), Japan. This parasite needs two hosts to complete its life cycle; the gray-sided vole as its intermediate host and the red fox as its final host. We found that: (1) Infection rates in foxes depended on the current-year abundance of voles in all three study areas, particularly in Abashiri. (2) In addition to this direct density-dependence, delayed density-dependence between the infection rate and the prior-year abundance of voles was detected in Nemuro and in Kushiro. (3) The regional differences in density-dependence pattern were related to regional differences in the winter food habits of red foxes: in Abashiri the proportion of voles in the fox’s diet greatly decreases in winter, while the proportion remains high in winter in Nemuro and in Kushiro, probably because of shallower snowpack. These results suggest that infection rates in foxes in Abashiri were less influenced by the prior-year prevalence, since the infection cycle might be interrupted in winter, when voles became less important in fox’s diet. In contrast, the state of the prevalence may carry over from year to year in Nemuro and in Kushiro, because red foxes continue to eat a considerable amount of voles throughout year. The regionally contrasted results for the relationship between infection rate in foxes and vole abundance were parallel to the regional difference in fluctuation pattern of vole populations, which are highly variable in Abashiri area, but less variable in Kushiro-Nemuro area. Drastic change in vole populations appears to affect the host-parasite system.     

Annual survival rate and age structure of habu,Trimeresurus flavoviridis (Viperidae), on Minna island, Japan: Estimation from removal trapping

A population of a viperid snake,Trimeresurus flavoviridis, was studied over 10 years by removal trapping on a small subtropical island in Japan. The sex ratio of trapped individuals changed seasonally, but was not biased to either sex in the whole sample of 258 individuals. The age of each individual was estimated through the size structure and the age-size relationship. The minimum number of individuals at the beginning of the study was estimated through accumulating older individuals trapped in the subsequent years. By assuming an annual natural survival rate in the course of this accumulation, an age structure was simulated which led to calculate a resulted natural survival rate. The assumed rate of 0.62 fitted best to the resulted one. The annual trapped proportion estimated on the simulated absolute number of individuals was higher in older individuals than in younger ones with the overall mean of 16%.     

Population growth trends in India: 1991 census

The decennial census counted the total population of India at 843.931 million as of the sunrise of March 1, 1991. The total is 160.6 million higher than that of a decade earlier in 1981. The actual census count exceeded by 45 million the official projections for 1991 based on the 1971 census. However, the official projections for the same year based on the 1981 census fell short by 7.6 million only. Most of the observed differences are explained by the slower decline in the fertility levels. The population growth ratepeaked during 1971–81, perhaps in 1972–73 (based on the Sample Registration Scheme data). The average annualexponential growth rate declined marginally to 2.11 per cent (4.5%) after having remained at a plateau for the previous two decades of 1961–71 and 1971–81. At this point in time, the fertility and mortality trends indicate that India will reach the replacement level fertility [Net Reproductive Rate of Unity] by the years 2010–2015. It can be said with a greater degree of certainty that the official target of reaching the replacement level fertility by the year 2000a.d. will not be reached. Based on the 1991 census results, it can be said that India will reach the billion mark by the turn of the century. The World Bank projects a population of 1,350 million by the year 2025a.d., and a stationary population of 1,862 million by the year 2150a.d., assuming that the replacement level fertility [Net Reproductive Rate = 1] in India is reached about the year 2015a.d.     

从第五次人口普查看世纪之交的广东人口状况

1990年以来 ,广东人口状况发生了深刻的变化。这些变化有的符合全国普遍规律 ,有的因受广东特殊社会经济环境的影响表现出不同特点。本文利用第五次人口普查最新数据 ,分析广东人口在数量、分布、素质和结构等方面的现状和特点