Population Biology
Populations
¡ Population growth is defined as an increase in size of
a population over time…
However, populations grow at different
rates.
¡
However, populations normally do not have linear
growth.
A population that is growing without any limits,
would have exponential growth…
Meaning that as the population gets bigger, it also will grow faster…
¡
But…Populations cannot keep exponential growth
for very long, because the environment would not be able to support it.
¡
The environment has a CARRYING CAPACITY for each
population…
¡
Carrying capacity is the number of organisms
that an environment can support.
¡
Once a population reaches its capacity, its
growth stops.
¡
Different sizes of populations will also have
different factors affecting them…
¡
Density Dependent Factors will affect larger
populations.
l
Examples: Disease, Competition, Parasites.
¡
These types of factors spread more quickly in
larger populations.
¡
Density Independent Factors affect any
population, regardless of size.
l
Examples: Temperature, Storms, Floods, and other
natural disasters.
Human Population Growth
¡
Demography:
¡
The study of
human population growth
-Growth
Rate
-Age
Structure
-Geographic
Distribution
¡
To determine the
growth rate, the birth rate is compared to the death rate.
¡
As more people
are born, an equal number must pass on in order for the growth rate to remain
level.
¡
However, humans
are living longer lives… our life expectancy (the age that a healthy person
would normally live is getting older all the time.
¡
In the U.S.
however, the population is having fewer children…
¡
Fertility rate is the number of children that
each woman has on average…
¡
While birthrate is just the number of births per
1000 people…woman or man
¡
Also the age of a country will tell a lot about
its future growth.
¡ Demographers study Age Structures of countries… This
tells how many people are in each age group…
l A younger aged population will grow more rapidly than
an older population.
l Immigration vs. Emigration
¡ Immigration is the movement into a country.
¡ Emigration is the movement out of a country.