Chapter 16


Consists of all the individuals of a species that live together in one place at one time.

Population Size

total number of individuals in a population

Population density

number of individuals per unit area


The pattern of distribution of organisms in a population

Population model

hypothetical population that attempts to exhibit the key characteristics of a real population

Exponential growth curve

Is a curve in which the rate of population growth stays the same, as a result the population size increases steadily.

Carrying capacity

largest number of individuals of a population that a environment can support

Density-dependent factor

a population-limiting factor whose effects depend on population density. e.g. resource availablity, competition.

Logistic Model

model of population growth that assumes finite resource levels limit population growth

Density-Independent factor

limiting factor that affects all populations in similar ways, regardless of population size


Species characterized by rapid growth, high fertility, short lifespan, and exponential population growth


species characterized by slow maturation, few young, slow population growth, and reproduction late in life

Hardy-Weinberg Principle

principle that allele frequencies in a population will remain constant unless one or more factors cause the frequencies to change

Gene Flow

movement of alleles into or out of a population due to the migration of individuals to or from the population

Genetic Drift

The gradual changes in gene frequencies in a population due to random events

Polygenic trait

trait controlled by two or more genes

Normal Distribution

bell-shaped curve that results when the values of a trait in a population are plotted against their frequency

Directional Selection

form of natural selection in which the entire curve moves; occurs when individuals at one end of a distribution curve have higher fitness than individuals in the middle or at the other end of the curve

Stabilizing Selection

form of natural selection by which the center of the curve remains in its current position; occurs when individuals near the center of a distribution curve have higher fitness than individuals at either end