Natural Childbirth Options
Parasites can be controlled either by increasing their death rate, or by decreasing their birth rate. Crop protection chemicals, and vertical resistance, achieve an increased death rate. Obviously, a secondary effect of an increased death rate is a reduced birth rate, Horizontal resistance produces a directly decreased birth rate. All the mechanisms of horizontal resistance tend to decrease both the growth rate, and the fecundity, of an individual parasite.
During the nineteenth century, the world population of people doubled from one billion to two billion. During the twentieth century, it increased to six billion. This exponential increase was due primarily to an improved medical science, which reduced the human death rate. The highest death frequency was the infant mortality rate, which was typically 50 before 1800. However, the reduced death rate, including a greatly reduced infant mortality, was not balanced by a corresponding decrease in the birth rate. It is not sufficiently appreciated that all of our modern environmental problems, without exception, are the result of our own over-population.
The functions of the agro-ecosystem are clear and unambiguous. The primary function is to feed people. There are also secondary functions that include feeding livestock, and supplying various industrial products, such as fibres, rubber, and industrial feedstock. Because of agriculture, the human species has increased the carrying capacity of its environment to many times that of our pre-hunting, pre-scavenging, food-gathering ancestors. By using cultural developments, such as the use of clothing, buildings, and fire, the human species has also increased its total environment, and has been able to spread into otherwise uninhabitable environments. More recently, medical science has greatly reduced the death rate, unfortunately without achieving a corresponding decrease in the birth rate. As a consequence, the
Reported four instars in this aphid, with the duration of each averaging 2.0, 2.1, 2.3, and 2.0 days, respectively. Parthenogenetic females gave birth to offspring 6-17 days after birth, with an average age of 10.8 days at first birth. The length of reproduction varied considerably, but averaged 14.8 days. The average period of life was about 23 days, but this was under caged conditions where predators were excluded. The daily rate of reproduction averaged 1.6 nymphs per female. The maximum number of generations observed annually during these studies was determined to be 20-21, depending on the year. In contrast, MacGillivray and Anderson (1958) reported five instars with a mean development time of 2.4, 1.8, 2.0, 2.1, and 0.7 days, respectively. Further, they reported a mean reproductive period of 20 days, mean total longevity of 41 days, and mean fecundity of 75 offspring. In the autumn, in response to change in day length or temperature, winged male and female aphids are produced...
During the spring and summer months, the ensuing adults are all female and they reproduce parthenogenetically. Adult wingless (apterous) females give birth to 30-50 nymphs in their life span, which is about 30-40 days. Their reproduction initially is high, but drops off markedly as they mature. Most aphids found during the summer months are wingless females only at high densities or when the host plant deteriorates are winged forms produced. The wingless females are grayish green, with a dark head, and pale-brown legs. The cornicles are dark and measure about 0.16 mm long. There is a double row of dark bars on the back, and the body is covered with a white powder or mealy secretion. The body measures 1.6-2.6 mm long, averaging about 2.5 mm.
The aphid varies in colour from light green to orange, measures 3 mm in length (see Figure 14.9) and has a complex life cycle, shown in Figure 14.8, alternating between the winter host (peach) and the many summer hosts such as potato and bedding plants. In spring and summer, the females give birth to nymphs directly without any egg stage (a process called vivipary), and without fertilization by a male (a process called parthenogenesis). Spread is by the summer flighted females. Only in autumn, in response to decreasing daylight length and outdoor temperatures, are both sexes produced, which having wings, fly to the winter host, the peach. Here, the female is fertilized and lays
A mystery presents itself, on the other hand, when we consider thermophilic microorganisms, since they prefer living at temperatures not commonly found in nature, such as hot springs, water heaters and compost piles. Their preference for hot temperatures has given rise to some speculation about their evolution. One theory suggests that the thermophiles were among the first living things on this planet, developing and evolving during the primordial birthing of the Earth when surface temperatures were quite hot. They have thus been called the Universal Ancestor. Estimated at 3.6 billion years old, they are said to be so abundant as to comprise as much as half of all living things on the planet. 25 This is a rather profound concept, as it would mean that thermophilic organisms are perhaps more ancient than any other living thing. Their age would make dinosaurs look like new-born babes still wet behind the ears, however extinct. Of course, we humans, in comparison, have just shown up on...
The rate at which a population is losing individuals. When the death rate is constant, and equal to the birth rate, the population size does not change. When the death rate exceeds the birth rate, the population growth is negative, and the population size declines. But when the birth rate exceeds the death rate, the population growth is positive, and the population size increases. When the positive population growth is very rapid, and it is called a population explosion. This rapid rate is typical of r-strategists. deBary
However, there was an external factor that had enormous influence on twentieth century agriculture. This was an unbalanced medical progress. The human death rate, particularly among infants, was drastically reduced by a greatly improved medical science. But the human birth rate was not correspondingly reduced in compensation. The result has been a human population explosion. Agricultural production has been increased accordingly,
The human disease caused by the ingestion of poisonous ergots. The symptoms of ergotism are a constricting of the blood vessels which can lead to gangrene, abortion in pregnant women, and death. Before the discovery of the cause of this disease, ergots were common in rye produced in a wet summer, and ergotism was a powerful incentive for the cultivation of potatoes in the rye districts of Europe, particularly in eastern Germany, Poland, and western Russia. Today, ergots are recognised and easily separated from rye before milling. They have a market value in the pharmaceutical industry as an aid to childbirth. Ergots
Pregnancy And Childbirth
If Pregnancy Is Something That Frightens You, It's Time To Convert Your Fear Into Joy. Ready To Give Birth To A Child? Is The New Status Hitting Your State Of Mind? Are You Still Scared To Undergo All The Pain That Your Best Friend Underwent Just A Few Days Back? Not Convinced With The Answers Given By The Experts?