Conservation and More Ecology
Carrying capacity is a measure of the steady-state density that the species can have for a particular habitat to support sustainably.
At carrying capacity, the environment replaces resources at the same rate that the species is using them. If carrying capacity is exceeded, the resources are eventually used up and the population size must decrease.
"resources" may be anything that a species need to live, including the ability to treat its our own wastes.
More on human carrying capacity here and here.
Population growth curves can sometimes indicate when a population has reached carrying capacity.
In other cases the population may exceed carrying capacity before eventually crashing. In nature population growth curves rarely resemble this textbook ideal.
Populations are usually limited when just ONE key resource is exhausted. The presence of other resources in abundance doesn't really help. This is sometimes called Liebig's law.
Historical human population growth. Appears to shows global carrying capacity for humans as hunter-gatherers is about 1-5 million worldwide. (i.e. about the poulation of Franklin county.)
Carrying capacity increased by transformation into agricultural society.
projected human growth. Note that this is at best a hypothesis. No evidence for this at all.
Humans currently "appropriate" 40% of the net product of terrestrial photosynthesis (Vitousek et al., 1986) and 25-35% of coastal shelf primary production (Pauly & Christensen, 1995), and these may be unsustainable proportions. [Global fisheries yields have fallen since 1989.] At the same time some global waste sinks seem full to overflowing.
Greatest Threats:
loss of agricultural land / topsoil loss (40% of worlds agricultural land already degraded)
loss of species diversity (especially those that are important for bio-remediation)
depletion of other key resources (oil, coal, phosphorous, water)
How real are the threats?
This UN Report generally regarded as most accurate and unbiased analysis of current situation.
oil use 1857 - 1960 = 1960 - 1970
coal use 1940 - 1970 = total use prior to 1940
Based on current projections, within something like 75 years, the world will have used up:
• all the world’s extractable coal,
• all the world’s extractable oil,
• all the world’s extractable natural gas, and
• all the world’s extractable uraninum-235.
The peak of production tends to occur when about half the resources are depleated.
US strategic oil reserve = 727 million barrels.
US oil use approximately = 580 million barrels each month.
True nature of problem is very simple: TOO MANY PEOPLE.
Current
calculations predict that the world CANNOT support more than 12 billion people.
At
curernt growth rates, the world population will exceed 12 billion in our lifetime.
Note utter futility of "recycling" and other non-population focussed
environmental efforts. Reducing per capita resource use by 50% will have no
effect at all on total resource use if current growth trend continues.
Problem of economic system that stresses GROWTH. Depends on increasing population
size.
Importance of delayed reproduction (Lengthening of generation time).
Glimmers of hope:
Maybe Human population will stabilize at 10 - 12 billion or be reduced through cultural changes and birth control or infertility.
Maybe new technologies will replace key resources in a way that will not damage the environment further. (Depends on truly astounding advances in science, particulary energy production. Whatever these new technologies are, they'd better happen fast.) (In light of the importance of developing alternative power sources very quickly, the cancelation of the US fusion project is extremely surprizing.)
Ecosytems have impressive adaptive and regenerative abilities. They can recover surprizingly quickly from many forms of damage. eg: River Thames
There
are, of course, some other, rather more unpleasant possibilities too.
