Source: Population Reference
Bureau
Not to be copied or reproduced without the
written permission of PRB
Background information:
In order to understand the pressure overpopulation places on the planet, it is necessary to understand a typical growth cycle. This is most represented by a bacterial population grown in a liquid media in a lab. A typical pure culture of bacteria does not increase in population significantly at first. This is due to low population densities as the bacteria are getting adapted to their environment, and is called the lag period of growth (see the growth curve). Following the lag period is an explosive population growth termed the exponential phase, which can go on indefinitely. After this, a stationary phase follows during which the total number of organisms remains constant. In this phase new organisms are constantly being produced while other organisms are dying so that the birth rate equals the death rate. Finally the last phase of growth is the death phase, in this period the overall number of organisms decreases so the death rate is greater than the birth rate.
Growth Curve:
Click on image for full size
Effects of overpopulation:
Two questions arise from this growth curve, one is what makes exponential growth end, and the other is what causes the death phase. The first answer is that in order for exponential growth to continue indefinitely there is a need for an endless food source. The second answer is that waste products build up within the growth media and becomes toxic to the organisms.
This analogy of bacteria and growth media can be applied to humans and the planet earth. In prehistoric times population densities were low and population numbers did not increase significantly or rapidly (3). Resources were plentiful during this time so the environment could easily accommodate the amount of wastes produced. As we go into exponential growth, populations are increasing more quickly and large amounts of resources are being utilized. As a result, wastes are being produced in ever-greater quantities. Exponential growth has some interesting and alarming consequences. Imagine a hypothetical strain of bacteria that has a division time of 1 minute (the doubling time is 1 minute). Assume that the bacteria are put in a bottle at 11:00 A.M. and the bottle is full at 12:00 noon. When was the bottle half full? The answer is 11:59 A.M. If you were an average bacterium in the bottle, at what time would you realize that you were running out of space? (4)
Here is the human population growth curve. This is our growth through out time. Notice where we are in the growth curve now.
