Ch.15 Notes
Population
Demography
Demographer
Population size
Emigration
Immigration
Why are small
populations more
likely to become
extinct?
Population density
Dispersion (list the
3 types)
Population model
Growth rate of a
population
Consists of all the individuals of a species that live together
in one place at one time.
Examples: all the alligators living in the Everglades this year
Study of human population size and the factors that
influence it
Example: largest demographic study in the US is the census
Scientists who studies human populations
determined by births, deaths, immigration, emigration and
limiting factors (biotic and abiotic) that determine carrying
capacity
Moving away
Moving into
Can be wiped out by one disaster
Difficulty in finding a mate
Inbreeding creates a genetically uniform population that is
more susceptible to disease and less able to adapt
Example: Cheetahs, Florida panthers
Number of individuals that live in a given space
Example: 5 individuals per acre
The way individuals are arranged (distributed) in space
a. random distribution;
least common (example:
many plants)
b. even distribution (example:
predators have territories)
c. clumped distribution;
most common (example:
grazing animals, plants near
a river, nesting sites)
Researchers try to predict how a population will grow by
making a model of the population, considering growth rate
and resources
The difference between the birth rate and the death rate
Can be fast, slow, zero, or declining (negative growth)
Drawing of population curves:
No growth
Rapid growth
Population increases
1
Slow growth
Negative growth
Population decreases
Reproductive
potential
Exponential growth
curve (draw one into
your notes)
The maximum number of offspring an individual can
produce
The rate of population growth if there are no limits to
growth
Is rare in nature (example: humans since the 20th century)
Logistic growth
curve (once carrying
capacity is reached,
the population size
only varies slightly)
Carrying capacity
Limits on carrying
capacity
Density-dependent
limiting factors
Density-independent
limiting factors
2
The population size that an environment can sustain.
Growth stops once carrying capacity is reached.
Density dependent and density-independent factors
Resources that become depleted as a population grows and
reduce or stop population growth: food, water, hiding and
nesting spaces, over-accumulation of waste, competition,
predation, human-made environmental problems
Example: If the carrying capacity for the field outside of our
school grounds is 8, then adding 8 more bulls would cause
starvation and over-accumulation of waste
Environmental conditions that limit growth:
Natural disasters (fires, floods, freezing, storms)
Affect all living organisms in a certain environment no
matter whether the populations are dense or sparse
Predator-prey
relationship
How is the growth
rate of a population
different below and
above carrying
capacity?
Example: I have two ponds, one with 10 fish and one with
100 fish. If the ponds freeze, the fish in both lakes will die,
not just the fish in the more densely populated lake.
The population of predators is limited by the population of
prey. The population of prey is limited by the population of
predators.
The growth rate is exponential until carrying capacity is
reached, then it plateaus until the carrying capacity changes.
The plateau is not a straight line, rather it varies slightly
while the population adjusts to environmental conditions
Change in carrying
capacity
can occur with new
environmental
conditions, such as
new predators,
change in plant
populations, manmade conditions
K-Strategist
R-Strategists
Population crash
3
Organisms that live in stable environments. Species
characterized by slow maturation, few young, slow
population growth, reproduction late in life, care for their
young
Example: tiger, whale
Organisms that live in rapidly changing environments;
characterized by rapid growth, high fertility, short life span
Example: roaches
Dramatic decline in the size of a population over a short
period of time
Activities
1.
2.
3.
4.
5.
Draw an exponential growth curve. Label both the x- and the y-axis.
Describe the curve (how is growth at the beginning versus the middle and the end)
What causes a population to grow exponentially?
Draw a logistic growth curve for an imaginary population of mice.
On this logistic growth curve, draw a new line for what happens to the population of
mice after 10 wolves have been introduced into the environment.
6. What type of organisms tend to organize themselves into even distributions?
7. Draw a population pyramid for a human population that is growing rapidly.
4