Understanding Populations
Section 1 How Populations Change in Size
Objectives
Describe the three main properties of a population.
Describe exponential population growth.
Describe how the reproductive behavior of individuals can affect the growth rate of their population.
Explain how population sizes in nature are regulated.
What Is a Population?
A population is a group of organisms of the same species that live in a specific geographical area and interbreed. A population is a reproductive group because organisms usually breed with members of their own population.
Properties of Populations
Density is the number of individuals of the same species that live in a given unit of area. Dispersion is the pattern of distribution of organisms in a population. A population’s dispersion may be even, clumped, or random. Size, density, dispersion, and other properties can be used to describe populations and to predict changes within them.
How Does a Population Grow?
A population gains individuals with each new offspring or birth and loses them with each death. The resulting population change over time can be represented by the equation below.
Growth rate is an expression of the increase in the size of an organism or population over a given period of time. It is the birth rate minus the death rate. Overtime, the growth rates of populations change because birth rates and death rates increase or decrease. For this reason, growth rates can be positive, negative, or zero.
For the growth rate to be zero, the average number of births must equal the average number of deaths. If the adults in a population are not replaced by new births, the growth rate will be negative and the population will shrink.Explanation:
