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Chapter 5 Characteristics of
Populations 5-1
1. Geographic
Distribution: “range”,
area inhabited by a
population
2. Density: # of
individuals per unit of
area
3. Growth Rate:
Increase, Decrease, or
Stay the Same
Population Growth
• 3 Factors that affect population growth
– # of births (birth rate)
– # of deaths (death rate)
– # entering and # leaving
• Immigration: movement of individuals into an area
(growth)
• Emigration: movement of individuals out of an area
(decrease)
Exponential Growth
• Exponential Growth: individuals
reproduce at a constant rate
J curve
– Ideal conditions with unlimited
resources are necessary for
exponential growth.
Ex: One bacteria cell reproduces
every 20 minutes.
How many after 20 min.?
How many after another 20 min?
How many after another 20 min?
How many after one day?
Logistic Growth
• Logistic Growth: when
population growth slows or
stops (due to decreased
availability of resources)
• S Curve
• Carrying Capacity: The
largest number of
individuals that an
environment can support
5-2 Limits to Growth
•
Limiting Factor: Causes population growth
to decrease
1.
2.
3.
4.
5.
Competition
Predation
Parasitism/Disease
Extreme Climates
Human Disturbances
Density Dependent Factors
• Density Dependent Limiting Factors – depends on
population size and density
• Factors act most strongly when population is large
and dense
– Ex: Competition
– Ex: Predation
– Ex: Parasitism
Density-Independent Factors
• Density –Independent Limiting Factors:
affect all populations, regardless of size
– EX: weather, natural disaster, seasons, and
humans
6-3: Biodiversity
• Biodiversity: sum total of genetically based
variety of all organisms
• Human threats to biodiversity:
–
–
–
–
Altering habitats
Hunting to extinction
Pollution
Introducing foreign species to new environments
Invasive Species
Pythons in Florida
Invasive Species Disaster
Why is biodiversity important?
• The greater the VARIATION in an ecosystem, the
more likely it is to RECOVER if there is a
disruption.
– Increased diversity = healthier environment.
• Biodiversity is a resource
–
–
–
–
Most pharmaceutical drugs from plants.
Future food sources, building materials, etc…
“Beauty, fascination, & wonder”
Recreation (ecotourism).
• Threatened
– Abundant in range, but decreasing in
numbers.
– At risk
• Endangered
– Very few remaining in natural range
– At risk for going extinct
• Extinct
– Local extinction – gone from local
range
– Ecological extinction – gone from
natural range (in zoos only)
– Biological extinction – gone from
Earth forever.
HIPPCO – Factors Leading to
Species Extinction
1. Habitat Loss
–
“Hot spots” with greatest impact: tropical areas, coral reefs, wetlands,
grasslands, water (fresh & salt)
2. Invasive Species
–
3.
Organisms not normally in habitat
Pollution
–
Air, water, soil impacts
4. Population
–
Arrival of humans and exponential population growth
5. Climate Change
6. Overexploitation
–
Ocean Fisheries