This herd of bison grazing in Yellowstone National Park has been in existence since prehistoric times. The herd is carefully monitored by the park’s scientists. They maintain accurate counts of the number of bisons, including the number of births and deaths that occur in the herd.

Data on the bison’s seasonal movements and use of the habitat are recorded. Yellowstone scientists also study the interactions of the bison population with other animal species, such as elk, that compete for the same food and may pass on diseases to the bison.

The scientists are studying the bison's population ecology. A population is a group of individuals of a particular species that inhabit a given area. And population ecology is the study of the interactions of a population and its environment.

The study of populations is not just abstract science. In the 1950s and 60s, studies of Yellowstone's bison population concluded that there were too many bison. The herd was reduced from 1500 to 400 individuals. In 1968, scientists decided to let nature determine the herd’s size, and today there are about 3900 bison in the park.

In contrast to Yellowstone, the searing hot Anza-Borrego desert in southern California is not home to large herds of mammals. The landscape is dominated by bushes that are adapted to conserve every drop of precious water. These creosote bushes look as if they’ve been neatly planted, with a similar distance between each bush. A population biologist studying these bushes might wonder why the distribution of the bushes is so uniform, and we’ll answer this question shortly.

In the first part of this activity, we’ll examine populations of organisms in terms of their spatial distribution and the distribution of ages in the population.

Next, we’ll look at models of population growth. By making some simple calculations, we can make predictions about the future size of a given population.

Finally, we’ll explore how the size of a population is regulated, and we’ll investigate the factors that limit population growth.

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