VBL 2.0: Population Biology: Introduction

Ecology is the scientific study of the interactions between organisms and their environment. The simplicity of this definition belies a tremendously complex area of biology. This complexity is driven by the use of term "environment". When used by an ecologist, environment refers to anything that is external to an individual organism. Therefore it includes not only abiotic (non-living) factors such as temperature, water availability, light intensity, etc., but also biotic (living) factors such other organisms of the same species, organisms that prey on or are prey to different species, etc. Thus, anything not a part of the organism can be considered part of that organism's environment.

Ecology is rooted in natural history. Although it originated primarily as a descriptive science, it has become increasingly quantitative and experimental. This is especially true for population biology. Population biology is the subdiscipline of ecology that studies populations (organisms of the same species living in the same general area) and the environmental controls that operate to regulate and control the size of these populations. Although the study of populations can be technically difficult, more and more data are being collected from field and laboratory experiments. Often, these experiments are designed to test very specific hypotheses. Based on their research, population biologists are increasingly able to devise mathematical models that help them to understand and explain the behavior of natural populations. Such models allow us to make predictions about the effects (impacts) of altering the parameters that govern the behavior of populations.

Although population biologists pay attention to underlying processes and events at all levels, they are especially interested in biological activity at relatively high levels of organization, such as populations (individuals of the same species), communities (groups of populations living in a common area), and ecosystems (communities and their physical environment). The overall goal of this research is to better understand how the "environment" influences populations.

This module is composed of three exercises that build on and complement each other sequentially. The first exercise, Population Growth, illustrates the dynamics of a single population. Specifically, it will allow you to visualize the relationships between population size, environmental carrying capacity, birth rate, and death rate. The second exercise, Predator-Prey I, illustrates the changes in two populations: a population of prey and a population of predators. Although both populations have their own individual population dynamics (as observed in Population Growth), they also influence each other. The Prey serves as the energy source for the predators. Finally, in Predator-Prey II the regulating factors of the first and second exercises are combined into a single model to illustrate how environmental carrying capacity and predation interact to influence the population dynamics of each population. Although more complicated, Predator-Prey II more closely approximates the situation in a natural setting.

Be aware that these population simulations have direct relevance to the human population. Although we are far more resourceful than most species when it comes to modifying our environment to support our ever- increasing numbers these models illustrate that there is an upper limit to our population as well. Indeed, it is through the careful development and verification of models such as these that we hope to gain a clearer understanding of the dynamics and limits of our own population.

To download and print a worksheet for this exercise, select Resources from the navigation bar to the left.

To begin, select Population Growth from the links in the navigation bar on the left.