# Chapter 5 bio population

What are the four main characteristics of a population?
geographic distribution
density
growth rate
age structure

What is a population’s geographic distribution?
It is the area inhabited by the population.

Another term for geographic distribution is
range

What is population density?
It is the number of individuals per unit area.

What is the equation with which you can calculate population
density?
population density= # of individuals
unit area

What three factors can affect population size?
a. The number of births
b. The number of deaths
c. The number of individuals that enter or leave the population

If more individuals are born than die in any period of time, how
will the population change?
it will grow

Immigration
The movement of individuals into an area
(the population grows)

Emigration
The movement of individuals out of an area
(the population decreases)

How will a population change if there is abundant space and food
and if the population is protected from predators and disease?
The population will
multiply, and the population size will increase.

When does exponential growth occur?
It occurs when individuals in a population reproduce at a constant rate.

What are three ways that a growth rate may be stated, or expressed?
It may be stated as a doubling time, a birthrate per female, or a percentage of growth per year.

Under ideal conditions with unlimited resources, how will a
population grow?
Such a population would grow exponentially.

When resources become less available, how does population
growth change?
It slows or stops.

When does logistic growth occur?
It occurs when a population’s growth slows or stops following a period of exponential growth.

What is the carrying capacity of the environment for a particular
species?
It is the largest number of individuals that the given environment can support.

What is a limiting factor?
It is a factor that causes population growth to decrease.

How do different limiting factors affect populations?
Some limiting factors affect a population more strongly as the population grows larger. Others limit a population’s growth regardless of the size of the population.

What is a density-dependent limiting factor?
It is a limiting factor that depends on
population size.

When do density-dependent factors become limiting?
They become limiting only when
the population density reaches a certain level.

When do density-dependent factors operate most strongly?
They operate most strongly
when a population is large and dense.

What are four density-dependent limiting factors?
Disease
Predation
Parasitism
Competition

When populations become crowded, what do organisms compete
with one another for?
They compete for food, water, space, sunlight, and other essentials of
life.

The mechanism of population control in which a population is
regulated by predation is called a(an)
predator-preyrelationship

What are the prey and what are the predators in the predator-
prey relationship on Isle Royale?
The prey are moose, and the predators are wolves.

Why does the wolf population on Isle Royale decline following a
decline in the moose population?
The wolf population declines because there is less for the wolves to feed upon.

How are parasites like predators?
Like predators, parasites take nourishment at the expense of their hosts, often weakening them and causing disease or death.

A limiting factor that affects all populations in similar ways,
regardless of population size, is called a(an)
density-independent limiting factor

What are examples of density-independent limiting factors?
Examples include unusual
weather, natural disasters, seasonal cycles, and certain human activities, such as damming rivers
and clear-cutting forests.

What is the characteristic response in the population size of many
species to a density-independent limiting factor?
The population size characteristically
crashes.

How does the size of the human population change with time?
It tends to increase with
time.

Why did the population grow slowly for most of human existence?
Life was harsh, and limiting factors kept population sizes low.

Why can’t the human population keep growing exponentially
forever?
Earth and its resources are limited.

What is demography?
It is the scientific study of human populations.

What factors help predict why the populations of some countries
grow faster than others?
Factors include birthrates, death rates, and the age structure of the
populations.

The hypothesis that explains why population growth has slowed
dramatically in the United States, Japan, and much of Europe is
called the
demographic transition

Throughout much of human history, what have been the levels of
birthrates and death rates in human societies?
Human societies have had high birthrates
and equally high death rates.

What factors lower the death rate?
Advances in nutrition, sanitation, and medicine lower the death rate.

What do age-structure diagrams graph?
They graph the numbers of males and females in different age groups.

What do the age structures of the United States and of Rwanda
predict about the population growth of each country?
The age structure in the United
States predicts a slow but steady growth rate for the near future. The age structure in Rwanda predicts a population that will double in about 30 years.

By 2050, the world’s population may reach how many people?
It may reach more than 9 billion people.

What may cause the growth rate of the world population to level
off, or even slow down?
That may happen if countries that are currently growing rapidly move
toward the demographic transition.

What do many ecologists suggest will happen if the growth in
human population does not slow down?
There could be serious and lasting damage to the environment as well as to the global economy.

What kind of limiting factor depends on population size?
density dependent

What occurs when the individuals in a population reproduce at a constant rate?
exponential growth

What is the movement of individuals into an area called?
immigration

What occurs when a population’s growth slows or stops following a period of exponential growth?
logistic growth

What is a mechanism of population control in which a population is regulated by predation?
predator prey relationship

What is the tendency of a population to shift from high birth and death rates to low birth
and death rates called?
demographic transition

What is the largest number of individuals a given environment can support called?
carrying capacity

What is the scientific study of human populations called?
demography