Alternative approaches to population structure

There are three approaches to DNA identification: tectonic, halieutic and icarian, of which the tectonic is sensible, the halieutic impractical, and the icarian idiotic. The rationale and consequences of these approaches are detailed.Editor's commentsThe author captures the harsh tone that has often characterized the debate over the use of DNA for human identification. It should be mentioned that D.L. Hartl, E.S. Lander and R.C. Lewontin were invited to respond. The positions of these three authors are contained in their papers, listed in the Bibliography. Readers should note, in particular, Budowle and Lander (1994).     

Population priorities: the challenge of continued rapid population growth

Rapid population growth continues in the least developed countries. The revisionist case that rapid population could be overcome by technology, that population density was advantageous, that capital shallowing is not a vital concern and that empirical investigations had not proved a correlation between high population growth and low per capita income was both empirically and theoretically flawed. In the modern world, population density does not play the role it did in nineteenth-century Europe and rates of growth in some of today''s least developed nations are four times than those in nineteenth-century Europe, and without major accumulation of capital per capita, no major economy has or is likely to make the low- to middle-income transition. Though not sufficient, capital accumulation for growth is absolutely essential to economic growth. While there are good reasons for objecting to the enforced nature of the Chinese one-child policy, we should not underestimate the positive impact which that policy has almost certainly had and will have over the next several decades on Chinese economic performance. And a valid reticence about telling developing countries that they must contain fertility should not lead us to underestimate the severely adverse impact of high fertility rates on the economic performance and prospects of many countries in Africa and the Middle East.     

Alternative views of functional protein binding epitopes obtained by combinatorial shotgun scanning mutagenesis

Combinatorial shotgun scanning mutagenesis was used to analyze two large, related protein binding sites to assess the specificity and importance of individual side chain contributions to binding affinity. The strategy allowed for cost-effective generation of a plethora of functional data. The ease of the technology promoted comprehensive investigations, in which the classic alanine-scanning approach was expanded with two additional strategies, serine- and homolog-scanning. Binding of human growth hormone (hGH) to the hGH receptor served as the model system. The entire high affinity receptor-binding sites (site 1) of wild-type hGH (hGH_wt) and of an affinity-improved variant (hGH_v) were investigated and the results were compared. The contributions that 35 residue positions make to binding were assessed on each hormone molecule by both serine- and homolog-scanning. The hormone molecules were displayed on the surfaces of bacteriophage, and the 35 positions were randomized simultaneously to allow equal starting frequencies of the wild-type residue and either serine or a homologous mutation in separate libraries. Functional selections for binding to the hGH receptor shifted the relative wild-type/mutant frequencies at each position to an extent characteristic of the functional importance of the side chain. Functional epitope maps were created and compared to previous maps obtained by alanine-scanning. Comparisons between the different scans provide insights into the affinity maturation process that produced hGH_v. The serine and homolog-scanning results expand upon and complement the alanine-scanning results and provide additional data on the robustness of the high affinity receptor-binding site of hGH.     

Sex,drugs and moral goals: reproductive strategies and views about recreational drugs

Humans, unlike most other species, show intense interest in the activities of conspecifics, even when the activities in question pose no obvious fitness threat or opportunity. Here, we investigate one content domain in which people show substantial interest, the use of drugs for non-medical purposes. Drawing from two subject populations—one undergraduate and one Internet-based—we look at the relationships among (i) abstract political commitments; (ii) attitudes about sexuality; and (iii) views surrounding recreational drugs. Whereas some theories suggest that drug views are best understood as the result of abstract political ideology, we suggest that these views can be better understood in the context of reproductive strategy. We show that, as predicted by a strategic construal, drug attitudes are best predicted by sexual items rather than abstract political commitments and, further, that the relationship between factors such as political ideology and drugs, while positive, are reduced to zero or nearly zero when items assessing sexuality are controlled for. We conclude that considering morality from the standpoint of strategic interests is a potentially useful way to understand why humans care about third party behaviour.     

Conservation priorities for carnivores considering protected natural areas and human population density

We conducted a prioritization exercise for 47 terrestrial carnivores in North and Central America. We used 2 by 2 degree cells to explore the spatial patterns in overall richness, regionally endemic and threatened species and identified the hotspots (the top 10% of cells in each category). We obtained optimal minimum sets of cells to represent each carnivore either (1) at least once, (2) three times, or (3) in at least 10% of its regional distribution range. Our analysis considered cells with 50% or more of their area protected, and considered human population density (HPD) per grid cell, excluding the top 10% cells with higher HPD. We found low congruence among hotspots, suggesting these should not be used alone in directing conservation strategies. About 7, 18 and 84 grid cells are needed to reach each representation goal, respectively. A much higher number of protected cells are needed to achieve the same goals. Representing 10% of each species’ distribution range required optimal sets of 47 additional cells to complement the protected cells. Irreplaceable cells had a similar or higher HPD than average values for all cells. By excluding the top 10% of cells with higher HPD, irreplaceable cells in optimal sets had much lower average HPD, but three species cannot be represented at all. By defining conservation priorities and proposing optimal networks of areas needed to represent all carnivores in the region, actual conservation efforts can be reviewed and revised. Furthermore, if our results are incorporated into a general strategy, limited resources available to conserve carnivores might be directed more efficiently.     

Alternative modes of population growth inhibition in a human lymphoid cell line growing in suspension

Using a human lymphoid cell line grown under continuous culture conditions, two distinct plateau states were induced, either by lack of sufficient medium-supplied nutrient, or by other unknown mechanisms dependent on cell density. Flow microfluorometric measurements show that growth arrest due to nutritional insufficiency results in an accumulation of cells with G1 DNA content. In contrast, growth arrest due to high cell density is not associated with an altered distribution of cells with respect to DNA content as the population progresses from exponential to plateau state growth. Cell size decreases with progression of the plateau state induced by either type of growth arrest. Cells in a plateau state induced by high cell density utilize glucose and incorporate exogenous amino acid into protein at approximately the same rate as exponential cells. Proliferating, high cell density, plateau state cells have cell cycle phase durations similar to exponential cells. The stable, plateau state cell density is maintained by cell loss. No stable, unbound growth inhibitory factor was found in the medium of density-inhibited plateau state cultures.     

Fertility and population policy in two counties in China 1980-1991

A survey of women in two highly developed rural counties of China, Sichuan and Jiangsu Provinces, was carried out in late 1991, to gain information about demographic and economic change between 1980 and 1990. Three separate surveys were conducted: the first a questionnaire administered to married women aged 30-39, eliciting information about childbearing and contraception, as well as the social and economic background of the respondents; the second, focus group interviews emphasizing the motivation for childbearing. Official information about the selected villages, townships and counties was also collected. National level data in 1987 show that individual reproductive behaviour in China failed to conform to a universal, effectively implemented, population policy. They imply either a spatial range of policies, or great diversity in the demand for children, or perhaps a combination of both. Such diversity in reproductive behaviour is also found in the study area. The purpose of the analysis was to examine the diversity in reproductive behaviour and contraceptive practice, and to discover whether differentials are influenced by area, or else exist between individuals within areas. If the former, then the explanation may be found in differences in policy formulation and implementation between areas: and if the latter, to demand for children, or else differential application of policy restrictions. The main findings were that: (1) the explanation of the pattern of fertility and contraceptive use is to be found at the individual level (within locations) rather than in policy differences between administrative units; (2) the association between income and number of children is negative, as is that between income and the propensity for uniparous women to remain unsterilized. The theory that privilege may be exercised to gain concessions from birth planning cadres is therefore not supported; (3) ideal family size differentials are largely absent, showing that social (education) and economic (income, occupation) characteristics are not responsible for differences in reproductive motivations, and implying that the nature of the demand for children is very different from that in most rural areas of the Third World; (4) data on ideal family size by sex of the existing offspring indicate only a weak preference for sons. The low demand for children, and the weak son preference, may both be explained by the social acceptability of uxorilocal marriages, and of village endogamy, together with the prohibitive costs of children, and especially of sons. This partly results from the expense of education, but most mothers emphasize marriage costs. It is speculated that the circumstances responsible for the escalating costs of children in the two countries are likely to pertain in growing areas of the country, with the privatization of education and health services, the declining support of collective institutions, and the replacement of this function by kinship networks. These on-going changes imply that any policy of reproductive restriction for the purposes of population control is likely soon to meet with diminishing resistance; and it may later be rendered unnecessary in the eyes of government officials, as fulfilled reproductive intentions lead to a fertility level below replacement level.     

Optimal fishery policy for size-specific,density-dependent population models

Optimal harvest policy is derived for a size-specific population model based on the continuity equation. In this model both growth and recruitment rates can depend on either the number of individuals of specific sizes in the population or the level of food available. Necessary conditions for values of fishing pressure and size limit that maximize the present value of the resource are obtained and are interpreted in economic terms. The general solution obtained here reduces to solutions obtained previously for some special cases: the single age-class model, and the linear age-dependent model. Solutions involving constant fishery policy are sought for several different, specific versions of the general model. In each of these versions a constant policy solution is not optimal. This implies that for a general, realistic model the policy that maximizes present value is a time-varying or pulse fishing policy. The theoretical and practical implications of the results are discussed in the light of existing results.     

Current views on the population structure of plasmodium falciparum: Implications for control

In recent years there has been a considerable debate on the population genetic structure of malaria parasites. Work on this subject has been revolutionized by the advent of the polymerase chain reaction (PCR) technique, which has made it feasible to study the genetic diversity of parasites in small samples of infected blood, allowing extensive surveys of natural parasite populations to be made. In addition, the technique can be applied to the mosquito stages of the malaria parasite, allowing direct assessments to be trade of the frequency of crossing between parasite clones in Nature. Studies on Plasmodium falcjparum in a wide range of malaria-endemic regions are now revealing the relationship between parasite population structure and malaria epidemiology. In this article, Hamza Babiker and David Walliker review recent work in this field, and discuss how such knowledge might be used to advise on the future deployment of control measures such as antimalarial drugs and possible malaria vaccines.     

A trans‐national monarch butterfly population model and implications for regional conservation priorities

1. The monarch has undergone considerable population declines over the past decade, and the governments of Mexico, Canada, and the United States have agreed to work together to conserve the species. 2. Given limited resources, understanding where to focus conservation action is key for widespread species like monarchs. To support planning for continental‐scale monarch habitat restoration, we address the question of where restoration efforts are likely to have the largest impacts on monarch butterfly (Danaus plexippus Linn.) population growth rates. 3. We present a spatially explicit demographic model simulating the multi‐generational annual cycle of the eastern monarch population, and use the model to examine management scenarios, some of which focus on particular regions of North America. 4. Improving the monarch habitat in the north central or southern parts of the monarch range yields a slightly greater increase in the population growth rate than restoration in other regions. However, combining restoration efforts across multiple regions yields population growth rates above 1 with smaller simulated improvements in habitat per region than single‐region strategies. 5. S ynthesis and applications: These findings suggest that conservation investment in projects across the full monarch range will be more effective than focusing on one or a few regions, and will require international cooperation across many land use categories.     

Variation in population structure and dynamics of montane forest tree species in Ethiopia guide priorities for conservation and research

The greatest extent of Afromontane environments in the world is found in Ethiopia. These areas support exceptional biodiversity, but forest cover and ecological integrity have declined sharply in recent decades. Conservation and management efforts are hampered in part by an inadequate understanding of the basic ecology of major tree species. We investigated population structure and inferred population dynamics from size frequency distributions of 22 forest tree species encountered in montane forests of Ethiopia. We collected new empirical data from four sites in the Bale Mountains, where some of the country's most extensive and least disturbed forests remain, and conducted a systematic review and analysis of all such studies that reported population structure for one or more of these species in Ethiopia. Thirteen widespread montane tree species showed a reverse‐J size distribution, indicating a relatively stable population structure. Six other species had size‐frequency distributions that indicate episodic recruitment and/or removal of certain size classes. Specific causes of these patterns are uncertain: they may involve timber harvesting, herbivory, fire, or natural disturbances, but patterns were inconsistent and locality dependent. For three other tree species, existing data are inadequate for any interpretation of population structure and dynamics. A species of particular conservation concern that emerged from this analysis was Hagenia abyssinica, which was found in all areas to consist only of larger individuals with no recent recruitment. For management and conservation purposes, the species in most urgent need of new research are those with inadequate or inconsistent data, and H. abyssinica.     

Alternative strategies in the acquisition of home ranges by male pine martens in a high-density population

Two strategies of home range acquisition by male subadult pine martens (Martes martes) were described from a high-density population inhabiting Bia?owie?a National Park. Four mother?Coffspring pairs were identified by genetic parentage assignments. Four subadult males showed two different strategies of home range acquisition: dispersal and sedentary. The dispersing males used an area 4?C10 times larger than in sedentary subadult males. A sedentary subadult male used his natal area with his mother, and in the following mating season, this male left this area and established a home range that overlapped greatly with another unrelated female near the natal range. A similar high overlap between another subadult male and an unrelated adult female persisted for 3?years. After the death of this female, the male extended his range to overlap slightly with two to four other females. The sedentary strategy adopted by some subadult males may explain the great variation in spacing patterns of solitary mammals.     

马尔萨斯"警醒"与中国人口的国家干预政策

1958～1979我国明显处于马尔萨斯"诅咒"或"陷阱"时期,谷底在1960年.1949年以来的实践证明"警醒"或"陷阱"最主要作用是促进"政府干预"性质的"基本国策(计划生育)"的诞生和实施.本文利用总和生育率(TFR)模型P n =(TFR/ 2)P n-1计算了如果"不实行"计划生育政策,从1949年起政策支持T...     

The ethics of population policy: emphasizing female sterilization in the third world

Rapid population growth in the Third World is a major social and economic problem, with attempts having been made to reduce the rapid growth rate through national family planning programs. Policies used by the programs, especially those concerning female sterilization, need to be examined to determine whether they are ethically acceptable. Such an analysis of the ethics of family planning policies raises awareness of not only the population problem, but also of the potential which exists for violating human rights when attempts are made to reduce population growth. The analysis also points to the need which exists in the Third World to create family planning programs which protect basic human rights. The population problem, reproductive rights, family planning programs, ethical principles, the ethics of incentives, alternatives, and decreasing maternal mortality are discussed.