Whether we're investigating bison in Yellowstone National Park or creosote bushes in the desert, population ecology is the branch of biology that studies the interactions of organisms and their environment.

When studying populations, we can gather important clues about the structure of the population by studying both its spatial distribution and its age distribution.

Because so much information about population structure is numerical, mathematical models are useful in predicting how populations will grow. The exponential model of unlimited population growth is not realistic in most situations because populations are limited by the carrying capacity of their environment. For this reason, logistic models predict the growth of real populations more accurately than exponential models.

Both density-dependent and density-independent factors regulate population size. Density-dependent factors include overcrowding and scarce food supplies. Examples of density-independent factors are harsh winter weather and hurricanes.

A number of organisms go through population cycles. Such cycles are usually due to environmental factors. The population cycle of snowshoe hares in Canada and Alaska is thought to be related to the available food supply. The associated cycle in the numbers of lynx may be related to the number of hares available for them to feed on.

The human population is currently growing at an exponential rate. American white settlers arrived on the Mayflower in 1620. At that time, there were about 500 million people in the whole world. Today, the number is just over 6 billion, or about 12 times the number when Thanksgiving was first celebrated.

Copyright 2006 The Regents of the University of California and Monterey Institute for Technology and Education