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
A population’s size is the number of individuals it contains.
Population density measures how crowded a population is.
(Expressed as the # of individuals per unit of area)
Dispersion is the spatial distribution of individuals
within the population.(clumped, even, or random)
Growth Rate = Change in # of individuals
÷
Time
Four factors determine whether the population
grows, shrinks, or stays the same:
1.
2.
3.
4.
Birth Rate
Death Rate (mortality rate)
Immigration
Emigration
 Exponential
Growth: Population increases
rapidly after only a few generations
Forms a J-Shaped growth curve
 Logistic
Growth: Builds on the exponential
model, but accounts for the influence of
limiting factors.
Limiting Factor = Restrains the growth of a population
Includes carrying capacity: The maximum #
of individuals that can be supported with the
available environmental resources.
Forms an S-shaped curve
At Carrying Capacity (K) – Birth Rate = Death Rate
 Density-Dependent
Limiting Factor:
Limits a population only when the population
reaches a certain density.
Examples: Resource Limitations
(shortages of food or nesting sites)
Competition, Predation, Parasitism, Disease
Regulates population size
Moose
Wolves
 Density-Independent
Limiting Factor: Affect
all populations in the same way regardless of
density
Examples: Natural disasters (floods,
fires, hurricanes, tornadoes)
Many human activities
 Causes
a growing or stable population to
collapse suddenly
Forms a Boom-and-Bust Curve
 Shows
the likelihood of survival at different
ages throughout the lifetime of the organism.
3 TYPES
Type I: Likelihood of dying is small, until late in life
(humans)
Type II: Probability of dying does not change
throughout life (linear) – some species of birds
Type III: Organisms that are very likely to die when
young (Oysters, salmon, many insects)
Hydra is a genus of simple, fresh-water animals possessing radial symmetry.
Hydras are predatory animals belonging to the phylum Cnidaria and the class
Hydrozoa. They can be found in most unpolluted freshwater ponds, lakes and
streams in the temperate and tropical regions by gently sweeping a collecting
net through weedy areas. They are usually a few millimeters long and are
best studied with a microscope.
Hydras mainly feed on small aquatic invertebrates
such as Daphnia and Cyclops. All species of Hydra
exist in a mutual relationship with various types of
unicellular algae. The Hydra affords the algae
protection from predators and in return, photosynthetic
products from the algae are beneficial as a food
source to the Hydra.
 Age
Structure: The distribution of individuals
among different ages in a population.
 Presented in graphs
U.S.
Population
Rwandan Population
 Hunter-Gatherer
Society
Agricultural Society
 Industrial
Society (1700’s)
Led to severe
environmental
damage
What major event caused an
increase in the human population?
Development of the Germ Theory of Disease
Identified bacteria and other microorganisms as
the agents responsible for many diseases
Improved hygiene
Sterile surgery
Better methods of waste disposal
Water treatment
Louis Pasteur
(1822-1895)
Agriculture
begins
Industrial
Revolution
begins
Plowing
and
irrigation
Bubonic
plague
In 1798 the English economist, Thomas
Malthus, observed that babies were being
born faster than people were dying.
___________________________________
Malthus reasoned that if the human population
continued to grow unchecked, sooner or later
there would be insufficient living space and
food for everyone.