# 2.1: Introduction

Learning Objectives

At the end of this, chapter students will be able to:

• Define the variables in the exponential and logistic growth equations.
• Use the exponential and logistic equations to predict population growth rate.
• Compare the environmental conditions represented by the exponential growth model vs. the logistic growth model.
• Define carrying capacity and be able to label the carrying capacity on a graph.
• Compare density-dependent and density-independent factors that limit population growth and give examples of each.
• Interpret survivorship curves and give examples of organisms that would fit each type of curve. Ecology is a sub-discipline of biology that studies the interactions between organisms and their environments. A group of interbreeding individuals (individuals of the same species) living and interacting in a given area at a given time is defined as a population. These individuals rely on the same resources and are influenced by the same environmental factors. Population ecology, therefore, is the study of how individuals of a particular species interact with their environment and change over time. The study of any population usually begins by determining how many individuals of a particular species exist, and how closely associated they are with each other. Within a particular habitat, a population can be characterized by its population size (N), defined by the total number of individuals, and its population density, the number of individuals of a particular species within a specific area or volume (units are number of individuals/unit area or unit volume). Population size and density are the two main characteristics used to describe a population. For example, larger populations may be more stable and able to persist better than smaller populations because of the greater amount of genetic variability, and their potential to adapt to the environment or to changes in the environment. On the other hand, a member of a population with low population density (more spread out in the habitat), might have more difficulty finding a mate to reproduce compared to a population of higher density. Other characteristics of a population include dispersion – the way individuals are spaced within the area; age structure – number of individuals in different age groups and; sex ratio – proportion of males to females; and growth – change in population size (increase or decrease) over time.