Ecology level three, Limits

WHAT IS CARRYING CAPACITY?
from the Carrying Capacity Network

A common fallacy is to equate existing and seemingly open or "unused" spaces with the kind of resources and ecologically productive land needed to support human life under modern conditions. In fact, the criterion for determining whether a region is overpopulated is not land area, but carrying capacity.

Carrying capacity refers to the number of individuals who can be supported in a given area within natural resource limits, and without degrading the natural social, cultural and economic environment for present and future generations. The carrying capacity for any given area is not fixed. It can be altered by improved technology, but mostly it is changed for the worse by pressures which accompany a population increase. As the environment is degraded, carrying capacity actually shrinks, leaving the environment no longer able to support even the number of people who could formerly have lived in the area on a sustainable basis. No population can live beyond the environment's carrying capacity for very long.

The average American's "ecological footprint" (the demands an individual endowed with average amounts of resources, ie, land, water, food, fiber, waste assimilation and disposal, etc. puts on the environment) is about 12 acres, an area far greater than that taken up by one's residence and place of school or work and other places where he or she is. We must think in terms of "carrying capacity" not land area. The effects of unfettered population growth drastically reduce the carrying capacity in the United States.

"...all of my colleagues and all of our students are scared witless about the state of the planet because it's so clear that we already have exceeded carrying capacity." Quote from KQED TV
www.kqed.org/tv/productions/populationbomb/hope/popandr.html

"Given the uneven distribution of population and resources, it's hard to comprehend the problem. Few of us fully understand just how small is the fraction of Earth capable of supporting human life. This exercise makes it clear."
www.kqed.org/tv/productions/populationbomb/danger/quotes.html

Materials: an apple, a knife, some graph paper, and some worksheets.
The apple is to represent Earth. Slice the apple into quarters. Save one quarter. It represents the total land area of the earth. What do the remaining quarters represent? [the oceans of the world]

Slice the land quarter in half. Set aside one of the pieces. The portion set aside represents the land area that is inhospitable to people. What comprises it? [the polar areas, deserts, swamps, high or rocky mountains] What fraction is left? [1/8] It represents human habitat - land where people live but do not grow the food.
Slice the remaining 1/8 piece into four equal sections and set aside three of these. What fraction is left? [1/32] The three 1/32 pieces set aside represent areas too rocky, too wet, too cold, too steep, or with soil too poor to produce food. They also contain the cities, suburban sprawl, highways, shopping centers, schools, parks, factories, parking lots, and other places where people live but do not grow food.

Carefully peel the skin off the 1/32 slice. This represents the food-producing soil upon which humankind depends. It is a fixed amount of land with topsoil less than five feet deep. Although advanced agricultural technology has increased food production per acre, each person's share of this food-producing land becomes smaller as the population increases.
Familiarize yourself with the term "carrying capacity". Earth is comprised of about 34 billion acres of land. As the population grows, each of our shares of land decreases. However, it is difficult to assess the amount of land we each need because the term is relative to our values and standard of living. Determine land area per person, keeping in mind that not all land is habitable.
Why is it important to protect our natural resources? What types of development threaten these resources? How does population growth impact these resources? Discuss the difference in the impact on resources from industrialized countries versus less developed countries.
NB: This model does not account for fish production from the 3/4 of the area representing the Earth's oceans. However, only approximately 1/10 of the ocean area produces fish that people eat and many species have been depleted and are in danger of becoming extinct due to over-harvesting.

"The results of human reproduction are no longer solely the concern of the two individuals involved, or of the larger family, or even of the nation of which they are citizens. A stage has been reached in the demographic developement of the world when the rate of human reproduction in any part of the globe may directly or indirectly affect the health and welfare of the rest of the human race. It is in this sense that there is a world population problem." Harold F. Dorn, 1962