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At least 1,603 records · Page 89Linked to original sources
PubMed2002

The stability of internal equilibria in predator-prey models with breeding suppression.

We present two models that represent the suppression of breeding by prey in response to short-term increases in predation pressure. For both of these models, we have been able to produce analytic conditions for the local stability of the interior steady state, in terms of the values of combinations of these parameters. Although our models are as simple as possible to capture the effect of breeding suppression, the expressions for local stability, even in their simplest form, are complex. Thus, we come to the important conclusion that there is no simple and general rule for the effect of the behaviours described here (anti-predatory breeding suppression and prey switching by predators) on the stability of population dynamics. Rather, effects will be system specific. However, we hope that the results and methodological framework outlined here will provide a useful tool for others to investigate the consequences for particular real systems.

Animals↗
PubMed2004

A proposal on a contribution of space biological sciences to sexual health in the human space life.

Sexuality is a basic property of the human being and provides an important background for the human life and society. The present situation in the world strongly suggests that the human being will extensively and intensively spread out in space and the population in space, particularly on the space stations in orbit, moon and possibly Mars, will rapidly increase during this century. Therefore sexual health will become a serious issue for the development of space and a better life of the human in the space environment. It is not too early to consider sexuality in the space life and to discuss how to maintain sexual health, how to control it in the space society, or whether it should be controlled. Space biological sciences should be the key and play an important role in studying scientifically sexuality especially the sex, sexual behavior and reproduction in the space environment.

Aerospace Medicine↗
PubMed1991

Adolescent sexuality and public policy.

In recent decades, various attempts have been made to determine the level of sexual activity among adolescents. This information has been used in the planning and evaluation of sex-related programs. However, there is a flaw in using only the initial estimates of the behavior--that a sexually active person is defined as one who has had sexual intercourse. This narrow definition distorts the perception of adolescent sexual behavior. Sexual activity can more accurately be designated by focusing on the actual frequency with which teenagers have sex. In this research report, adolescents were considered sexually active if they had had sex within the last four weeks. Using this definition, adolescents were found to be substantially less sexually active than has been previously reported. This finding was then used to look at various policy decisions in the areas of sex education, family planning, and sexually transmitted disease prevention.

Adolescent↗
PubMed1991

[Medico-social characteristics of young people at the stage of creating a family].

The article provides a comprehensive characterization of young people on the eve of creating a family including the evaluation of socioeconomic, socio-demographic, socio-psychological features sexual behaviour of brides and bridegrooms before marriage, the use of contraceptives, etc. An analysis is also made of the morbidity among brides and bridegrooms and comprehensive evaluation of their health status with regard to the group of health.

Adolescent↗
PubMedDate not supplied

The risk of premarital first pregnancy among metropolitan-area teenagers: 1976 and 1979.

Among sexually active teenage women living in metropolitan areas of the United States, the risk of premarital pregnancy within two years of first sexual intercourse rose from 32 percent in 1976 to 36 percent in 1979. As of 1979, 33 percent of unmarried white teenagers, and 43 percent of unmarried black teenagers, had conceived within 24 months of becoming sexually active. The increase in pregnancy risk between 1976 and 1979 was relatively greater for whites than for blacks at three, six and 12 months after first intercourse. The reverse was true at later intervals. The risk of pregnancy is disproportionately concentrated in the early months of sexual activity. Forty-five percent of all premarital pregnancies among those interviewed in 1979 had been conceived within the first six months of sexual activity, and 36 percent had been conceived within three months. In 1976, 27 percent of teenagers who had become sexually active before the age of 15 were premaritally pregnant within two years. By 1979, this proportion had risen to 41 percent--a 52 percent increase in the risk that accounts for almost all of the total three-year increase in premarital pregnancies among sexually active teenagers. The most pronounced increase in risk of pregnancy was registered among whites who became sexually active when they were younger than 15. Their 24-month probability of conception rose from 20 percent in 1976 to 39 percent by 1979. Levels of risk for unwed teenagers who initiated intercourse at ages 15-19 increased relatively little.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1980

Contraceptive efficacy: the significance of method and motivation.

The relationship between contraceptive failure and selected characteristics of users is examined using data collected in the 1970 and 1975 rounds of the National Fertility Study. Intention regarding future childbearing and choice of contraceptive method are found to be the most important considerations. Within categories of intention, choice of method appears to have an important influence on differentials by age and other characteristics. The longitudinal aspect of the study design permitted the inclusion in the analyis of certainty of intention, coital frequency, and women's perceptions of their own ability to control fertility.

Adolescent↗
PubMedDate not supplied

Influence of discipline of study on the sexual behaviour of Nigerian female students.

In this comparative study of the sexual behaviour of 476 Nigerian female students in tertiary institutions comprising of 243 students of the medical discipline of study (MD group) and 233 students of the non-medical discipline of study (NMD group), the overall incidence of sexual intercourse was 56.7 percent. The mean age at first sexual experience was not significantly different at & = 0.05 among the two groups. However, sexual exposure was significantly more prevalent among students of the non-medical discipline of study (NMD group)--69.1 percents compared to those of the medical discipline of study (MD group)--44.9 percent (p < 0.01). In addition, the frequency of sexual exposure was significantly higher among the former group, 5.5 +/- 6.8 times per month, than in the later, 1.7 +/- 3.8 times per month (t = 5.25 with 274 d.f.; p < 0.005). The incidence of pregnancy among the two groups of students 37.1 percent and 31.2 percent respectively for the NMD and MD groups showed no significant difference at & = 0.05. The reasons for the observed difference in the sexual behaviour between the students for the two groups are adduced. The overall implications of sexuality and the relevance of its management among the youth are also discussed.

Adolescent↗
PubMed2006

Phthalate affect the reproductive function and sexual behavior of male Wistar rats.

Phthalates are chemicals used in many industrial products (plastic toys, shampoos, soaps), and are suspected of inducing adverse effects on the male reproductive system. In the present study, we evaluated the effects of the plasticizer di-(2-ethylhexyl)-phthalate (DEHP) on the reproductive function and sexual behavior of male offspring rats, exposed in utero and during lactation (0, 20, 100 and 500 mg/kg per day by gavage). The effects produced clearly demonstrate the ability of DEHP to disrupt the androgen-regulated development of the male reproductive tract. Absolute and relative weights of androgen-dependent tissue organs (ventral prostate and seminal vesicle) were significantly reduced at the highest dose level tested (500 mg/kg per day). Impairment of male sexual behavior (500 mg/kg per day) was also observed. Moreover, the reduction in daily sperm production and epididymal sperm counts observed after administration of the highest dose suggests an impairment of the spermatogenic processes. Most of the adverse effects reported here were observed both during puberty and during adulthood, indicating permanent effects of in utero and lactational DEHP exposure.

Animals↗