Download Ecology of Populations

Population Ecology
How do Ecologist study
populations?
 Geographic range
 Density and distribution
 Random
 Uniform
 clumped
 Growth rate
 Age structure
Population growth
 Birth rate versus Death rate
 Immigration versus emigration
Exponential growth
 Larger the population grows, the faster it grows
 Organisms that reproduce rapidly
 Organisms that reproduce slowly
 Organisms in new environments
 “j” shaped curve
Population Questions
 Your rich uncle has just died and has left you 1 billion
dollars. If you accept the money you must count it for
eight hours a day at the rate of one dollar per second.
When you are finished counting, the billion dollars will
be yours and only then may you begin to spend it.
 Do you accept your uncle’s offer? Why or why not?
 How long would it take to count a billion dollars at this
rate? How long would it take to count a million dollars
at the same rate?
Doubling time
 Bacteria multiply by division. One bacterium becomes
two, two become 4, 4 become 8… For some bacteria,
the time for this division process is 1 minute.
 If you put one of these bacterium in a bottle at
11:00pm, the entire bottle will be full at 12am. When
would the bottle be half full?
Logistic growth
 “s” shaped curve
 As resources become limited, population growth slows
or stops, leveling off at the carrying capacity.
 Follows exponential growth
 Carrying capacity – max. number of individuals of a
particular species that a particular environment can
support
Limiting factors to population
 Separately or together, limiting factors determine the
carrying capacity of an environment for a species.
 Competition
 Predation
 Parasitism and disease
 Unusual weather
 Natural disaster
Density dependent vs.
Density independent
 Density dependent limiting factors affect density (# of
organisms per unit area) when density reaches a
certain level.
 Competition, predator/prey, parasitism
 Density independent factors – occur regardless of
population size
 Weather, natural disasters
Human Population
 Tends to increase
 Less predators/disease
 Improved nutrition, sanitation, medicine and health care
 Exponential growth
 Thomas Malthus predictions, population can only be
limited by war, famine and disease
Patterns of human growth
 Demography – scientific study of human populations.
 use birthrates, death rates and age structure to predict
growth or decline
 Demographic transition
 Change from high birthrates and death rates to low
birthrates and death rates.
 Japan, US and Europe have completed the transition
 South America, Africa and Asia are in stage 2