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Guest
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Originally Posted by Undertoad
Ah, ok. You took a paragraph out of the middle of the page.
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And you took a sentence out of context which started this all. In citing the wisom of Wikipedia, here was your cut 'n paste:
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According to projections by the Population Division of the United Nations revised in 2004, the population of the world will stabilize at 9.1 billion by 2050 due to demographic transition. The UN has consistently revised its population projections downwards over the last 10 years. Birth rates are now falling in most developing countries, while the population in many developed countries would also fall without immigration.
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You neglected to address or even quote the very next sentences in your Wikipedia article:
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David Pimentel, a professor of ecology and agricultural sciences at Cornell University, predicts that population outcomes for the 22nd century range from 2 billion people (characterised as thriving in harmony with the environment), to 12 billion people (characterised as miserable and suffering a difficult life with limited resources and widespread famine)...
Other studies have countered with the claim that the current population level of over six billion may be supported by current resources, or that the global population may grow to ten billion and still be within the Earth's carrying capacity. In The Skeptical Environmentalist, published in 2001, Bjřrn Lomborg argued that because of the falling rate of population growth, and because of new, alternative technologies, there is no problem with overpopulation. The assumptions that underlie these claims, however, have been strongly criticised. One criticism is that poor people can't afford such technologies. However, it is also possible the Earth is capable of sustaining more humans without the need for such technology.
In any case, many proponents of population control have averred that famine is far from being the only problem attendant to overpopulation. These critics point out ultimate shortages of energy sources and other natural resources under the Hubbert peak theory, as well as the importance of serious communicable diseases in dense populations, and war over scarce resources such as land area.
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Originally Posted by Undertoad
You still don't understand the meaning of the word "exponential" and are fighting hard against the notion of learning it.
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The feeling is mutual.
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Originally Posted by Undertoad
That word "if" is the operative word in that whole sentence:
Human population, if the number of births and deaths per person per year were to remain constant (but also see logistic growth).
If. But the number of births and deaths per person per year do not remain constant.
And then there's the last bit of that sentence, the bit you left out. Where it says but also see logistic growth. If you go to that page you find that it is an example of a function where growth appears to be geometric for a while, then slows, then stops. You also learn that it is another model for population growth. |
I will learn nothing of the sort. Any biological species will experience exponential growth until the ecosystem upon which it depends reaches carrying capacity. Usually, carrying capacity is determined by one or more limiting factors such as food supply, water, availability of certain key nutrients, etc.
From your Wikipedia article:
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The logistic function or logistic curve models the S-curve of growth of some set P. The initial stage of growth is approximately exponential; then, as competition arises, the growth slows, and at maturity, growth stops.
As shown below, the untrammeled growth can be modelled as a rate term +rKP (a percentage of P). But then, as the population grows, some members of P (modelled as − rP2) interfere with each other in competition for some critical resource (which can be called the bottleneck, modelled by K). This competition diminishes the growth rate, until the set P ceases to grow (this is called maturity).
A typical application of the logistic equation is a common model of population growth, which states that:
•the rate of reproduction is proportional to the existing population, all else being equal
•the rate of reproduction is proportional to the amount of available resources, all else being equal. Thus the second term models the competition for available resources, which tends to limit the population growth.
Letting P represent population size (N is often used in ecology instead) and t represent time, this model is formalized by the differential equation:
where the constant r defines the growth rate and K is the carrying capacity. The general solution to this equation is a logistic function. In ecology, species are sometimes referred to as r-strategist or K-strategist depending upon the selective processes that have shaped their life history strategies.
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Neither Wikipedia nor any ecologist who doesn't want to be laughed out of the profession would make the statement that logistic function is an alternative model for population growth. Logistic function is a set of variables and equations which are components in the study of population dynamics, NOT an alternative model to exponential growth.
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Originally Posted by Undertoad
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Not much.
Maybe they should start talking to other departments within their own outfit, such as the Food and Agricultural Organization of the United Nations I have traveled extensively in Northeastern Brazul and if forced to choose between one UN group versus the other, I can tell you from personal observation that the World Food Programme cheats and lies if that's what they think. Here is what I observed and what the FAO reports:
In Brazil poverty affects more than a quarter of the population - some 44 million people. In the nine states in north eastern Brazil, the poorest parts of the country, almost half of all families live on approximately a dollar a day.
The first priority of the new President, Luiz Inácio Lula da Silva, is to ensure that every Brazilian eats three times a day. He has launched an ambitious programme called Zero Hunger, with the support of FAO.
Hunger is the most extreme manifestation of the huge problem of poverty in Brazil. Few people die of starvation, but there is widespread chronic food insecurity and malnutrition. This means that people are unable to produce or gain access to enough food of an adequate quality for a healthy life. It is the hunger of the missed meal, and it is very debilitating.
The current situation needs urgent interventions and President Lula has given himself just the four years of his mandate to solve the problem. Will Brazil need emergency interventions?
In many countries, the very success of agriculture has been disastrous for poor rural people. Advanced countries have absorbed their surplus rural population in other sectors, allowing farm size to increase and economies of scale to take effect. But in most developing countries, small farmers have either had to remain on the land, often with a diminishing size of plot as families have grown, or tomigrate to the cities with no job in sight. Most chronically food insecure people are, therefore, small farmers or recent urban migrants who have fled rural destitution.
- The number of people who suffer from chronic undernourishment is not known accurately and is a subject of much debate. According to FAO's estimates, using methodology applied internationally, in 1998-2000, some 16.7 million Brazilians ( about 10 percent of the population) were chronically undernourished.
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Originally Posted by Undertoad
Which reminds me, I have some Chilean grapes in the fridge, and it's lunchtime.
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No comment.
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Originally Posted by Griff
Oh and Mari, words have meanings
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Not if you hang out with UT, they don't. 
Last edited by marichiko; 02-15-2006 at 12:33 AM.
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02-14-2006, 04:49 PM
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