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PubMed1990

[From twentieth to twenty-first century: Europe and its population after the year 2000].

The model of demographic transition predicts that in the final stages of the transition, the population will become stationary. However, during the past 20 years or so, the birth rate in the majority of industrialized countries has fallen below the death rate, and a continuation of this trend will ultimately result in a declining population. In the UN recent projections of world population growth, an attempt was made to salve the transition model by assuming that when faced with a reduction in numbers, couples will wholeheartedly respond by increasing their family size. The author presents a theoretical model in which he showed that during the final stages of the transition, it is likely that there are built-in mechanisms which will result in low birth rates, and that it is unlikely that fertility will return to replacement level. In addition to the scenario presented by the UN, there is another in which the birth rate remains below the death rate indefinitely. This catastrophic scenario would ultimately result in the disappearance of the human species. The author presents and compares both of these scenarios. Using some calculations by J.N. Biraben, he calculates the number of humans that would have been born between the beginning and end of the human species, as described by the catastrophic scenario and estimates this to be at 100 billion. In order to end on a more upbeat note, he than imagines a new demographic transition in which biologists have succeeded in extending the duration of a woman's reproductive life. They could then engage in 2 fertile unions during their lifetimes and thus save the species.

Birth Rate↗
PubMed1993

A study on socio-economic and intermediate variables on fertility.

"In this paper an attempt has been made to examine fertility differentials of currently married rural women [in Bangladesh] by their socioeconomic (viz, education of women, land ownership and family type) and demographic (viz, age at the first marriage, duration of breast feeding and duration of post partum amenorrhoea for the child) characterisation. This study is based on data collected from 995 currently married women of childbearing age. It has been found that women's (i) level of education (ii) age at first marriage (iii) duration of breastfeeding and (iv) duration of post-partum amenorrhoea, are inversely related with fertility. Joint family shows higher fertility than that of nuclear family and land ownership reveals [a] U-shaped relationship with fertility."

Amenorrhea↗
PubMed2003

[Ecophysiological effects of multiple cropping of winter wheat-spring corn-summer corn in Huanghuaihai Plain].

Compared to sequential cropping of winter wheat-summer corn and mono cropping of spring corn, the ecophysiological effects of multiple cropping of winter wheat-spring corn-summer corn in Huanghuaihai Plain were studied. The results showed that under the multi-cropping, the crops occupied higher spatial niches during the period of reproductive growth. Ecological factors such as light, temperature, and air were improved, and plane light acceptance was changed into multistory light acceptance, which made the relative intensity of illumination in crop communities increased. Moreover, soil temperature between rows and wind velocity in planting strips were also increased. All these changes were advantageous to increasing the intensity and velocity of grain filling. The chlorophyll content and photosynthetic rate in functional leaves of crops were higher, which was the main reason of yield increase under multiple cropping.

Agriculture↗
PubMedDate not supplied

[Normal development of the fruitfly Drosophila in VLF magnetic fields (author's transl)].

Attempts to substantiate irreversible actions of a variety of magnetic fields on the fruitfly, Drosophila melanogaster, have been successful and unsuccessful in about equal numbers. The most conspicuous mutagenic effects apparently induced by pulsed HF-fields failed to appear under continuous electromagnetic irradiation. This seems to correlate the observed damage with the VLF-components of the pulsed fields. The present investigation is motivated by the occurrence of these components both in the atmosphere and in the vicinity of electrical appliances. A strain of normally viable wild type males and subnormally viable Attached X y w females was used in which the yield, and the sex ratio, of the progeny indicate, respectively, the extent of developmental damage and of sex-linked recessive lethal mutation induced by the exposure of detrimental conditions. Evaluation of 73,800 flies from subsequent generations of a control group and two test groups raised in steady, or rotating, homogeneous 9.6 kHz magnetic fields of about 2.5 G did not reveal any developmental or hereditarc load in the test groups. (Pressman 1970; Mittler 1973).

Animals↗
PubMed1992

Termination of photorefractoriness in the brahminy myna, Sturnus pagodarum: role of photoperiods and gonadal hormones.

In brahminy myna a photosensitive species, long days caused full gonadal development followed by rapid regression, whereas short days inhibited these responses. Experiments were performed to investigate the effects of duration of photoperiod and gonadal hormones on the recovery of photosensitivity to long photoperiods in male birds. Groups of photorefractory birds were subjected to 8-, 9- or 11-hr daily photoperiods for 45 (6.5 weeks) or 63 (9 weeks) days and then transferred to 15 h daily photoperiods for 60 days to check for the regaining of photoresponsivity. A control group was held under 15L:9D throughout the period of study. Another experiment included three groups of photorefractory males, which were maintained on 9L:15D for 9 weeks and administered with, birth-1day-1 alternately for first 30 days olive oil or different doses (10 or 100 micrograms) of testosterone propionate (TP)/bird/day alternately for first 30 days, and then transferred to 15L:9D for another 30 days to test the recovery of photosensitivity. The results indicated that (i) a period of exposure to short daylengths is required to dissipate photorefractoriness, (ii) termination of photorefractoriness is dependent on the length and duration of photoperiods and (iii) TP inhibits the recovery of photosensitivity in a dose dependent manner.

Animals↗
PubMed2005

[Effects of aluminum stress on photosynthetic characters of soybean].

With three soybean (Glycine max) varieties Zhechun No. 2, Zhechun No. 3 and 9703 as test materials, this paper studied the effects of different aluminum (Al) concentration on their photosynthetic characters. The results showed that the leaf chlorophyll content decreased by 5%-35% when Al concentration increased. Al also affected various physiological functions, e. g., stomatal resistance increased by 10%-35%, stomatal conductance decreased by 10%-40%, photosynthetic and transpiration rate decreased by 5%-40% and 20%-50%, respectively, and water utilization efficiency decreased by 15%-50%. Al stress could inhibit the photosynthesis of soybean leaves, and the inhibition was more serious in vegetative than in reproductive growth period. In addition, three test soybean varieties had definite genetic difference in response to Al toxicity.

Aluminum↗
PubMed2005

[Influence of time of initiation of a prostaglandin F2alpha protocol in dairy cows with puerperal endometritis].

A field trial was conducted to elucidate the effect of the time of initiation of a repeated PGF2alpha-application in a 14 day interval for treatment of endometritis in dairy cows. On a commercial dairy farm in Brandenburg, Germany, a total of 494 dairy cows were examined by rectal palpation and adspection for signs of endometritis (vaginal discharge, enlarged uterus) between day 20 to 26 post partum (dpp). We performed two further examinations by rectal palpation and external adspection to monitor the puerperal phase (34.-40. dpp, 55.-61. dpp). All cows with symptoms of an endometritis were treated with PGF2alpha (0.15 mg R-Cloprostenol, Preloban, Intervet Deutschland GmbH Unterschleissheim) twice in a 14-day interval. In the group "Early" (n = 146) the first injection of Cloprostenol was administered at time of the 1st examination. In the group "Late" (n = 129) an identical treatment was administered in cows with endometritis, however it was started 14 days later (34.-40. dpp). The incidence of endometritis was 57.7% in the group "Early" and 53.5% in the group "Late" at the first time of examination. The 1st service conception rates for treated cows were 34% in the group "Early" vs. 37% in the group "Late". In the group "Early" differences were found in days open between treated cows with endometritis and untreated controls without symptoms of endometritis (99.1 d vs. 110.8 d, p > 0.05). In the group "Late", days open for treated (106.8 d) and untreated cows (108.0 d) were similar. The severity of endometritis influenced the percentage of cows pregnant at 200 dpp. Regarding cows with a severe endometritis (E2 and E3) the percentage of pregnant cows 200 dpp was higher in the group treated early (E2: 78.4%; E3: 80.0%) than in the group with the late initiation of the treatment (E2: 68.6%; E3: 54.5%, p < 0.05). Cows with a moderate endometritis (E1) had a similar percentage of pregnant cows (200 dpp) as the untreated cows without endometritis. It is concluded that application of PGF2alpha in the 4th and 6th week post partum in a 14 day interval in cases of severe endometritis is more effective than the application of the same treatment two weeks later.

Animals↗