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Population Ecology
• Group of organisms of a single species that
lives in a given area.
Studying Populations
– Geographic range (what is area inhabited by population?)
– Density (how many individuals in an area?)
– Distribution (how are they spaced out in their range?)
– Growth Rate (increasing, decreasing, staying the same?)
– Age Structure (how many mature reproducing individuals
versus juveniles?)
– Males to Females (only females can produce young)
Factors Affecting
Population Growth
• Birthrate:
– if more individuals are born than die the population grows
• Death Rate
– If more individuals die than are born the population shrinks
• Emigration: (individuals leaving) populations shrink
• Immigration: (individuals entering) population grows
Population Explosion
Mice in Australia:
• Will happen if:
– Population has all the food & resources it needs
– Free from predators and disease
– Waste is removed
• The size of each generation gets bigger and bigger
• Eventually a population’s growth will level off and
stabilize when the ecosystem reaches it’s carrying
Carrying Capacity
– Maximum population that can be supported
by the resources in the environment.
– Birth and death rates of an organism are
Limiting Factors
• Environmental factors affecting organisms
ability to survive
• Usually present in the shortest supply
• Can be biotic or abiotic
Examples of Limiting Factors:
– Amount of resources available (food water, nutrients,
nesting sites)
– Competition for resources (caused when niches overlap)
– Predation (Predators keep prey populations in check)
– Parasitism (how weakened are individuals by parasites?)
– Disease
– Natural Disasters & Unusual Weather
Human Population Growth
• For most of
human existence,
population grew
slowly and was
kept in check due
to many limiting
factors that kept
human death
rates high.
• Advances in civilization (especially after
the Industrial Revolution 1800s) reduced
the death rate substantially and increased
human lifespan:
– Medicine (better healthcare)
– Agriculture (better nutrition and more reliable)
– Sanitation (less contamination of food and
drinking water reduced disease)
• It can’t grow
forever, eventually
the resources will
become too limiting
Population Ecology Video:
Mouse Population Experiment:
– Human Population Growth Video:
Needs of a Growing
Human Population
• Food
• Energy: help keep us
warm and run our
• Living space for both
houses and farmland
• Resources
– Make housing, clothing
– Make all the other stuff
people have to buy
Effects of Human Population
Growth on the Environment
• Species are disappearing at a rate of
about one species per day
• Remember the most stable environments
have a high level of BIODIVERSITY
– (Many different types of species)
• Every species that is lost causes “ripples”
through an ecosystem.
• Can lead to extinction and
• Remember: Lowering
population of one species
affects others
• Ex: Blue Whale
Blue Whale:
History of Whaling:
• Ex: Bison:
• Historically, bison numbered an
estimated 20-30 million.
Unregulated shooting of bison, culminated in mass slaughters
during the 1870s, reduced the
population to 1,091 in 1889.
• Today, approximately 500,000
bison live across North America.
Most are not pure bison but rather
have been cross-bred with cattle
in the past and are raised as
livestock on ranches. Fewer than
30,000 bison are in conservation
herds, and fewer than 5,000 are
free-ranging and disease-free.
• Ex: Tasmanian Tiger (extinct)
Importation of Nonnative Organisms:
– Transfers organisms into communities where they
normally don’t exist
– Factors that would naturally limit it’s population growth
(predators, parasites) may not exist in the new
environment so population explodes
– This may displace other species through competition
for resources and disrupt the existing ecosystem.
– Ex:
– Starlings, goats, cats, pigs, japanese beetles, gypsy
moths, boxer crabs, zebra mussels, mugwort, purple
loosestrife, kudzu
Exploitation of Wildlife:
• Ex:
– Ivory (elephant and walrus tusks)
– Bird feathers
– Fur from beavers, otters, etc.
– Exotic animals for pet stores
– Animal parts for “traditional” medicinal
• Ex: Rhino horn
Poor Land Management:
• Growth of cities and
suburbs has destroyed
many natural habitats
• Deforestation
– Allows for soil erosion
• Draining of wetlands
– Destroys fish nurseries
• Soil used for farming can
become depleted of
nutrients (ex: Dust Bowl)
Water Pollution:
– Nitrates (from fertilizer runoff),
phosphates, oil, detergents,
heavy metals (like mercury),
plastic refuse
– Pollutants can be concentrated
in the food chain
• Biomagnification
Air Pollution:
– Acid Rain: sulfur and nitrogen oxides
produced by factories combine with water in
the air and fall as rain.
• Plants can wither and die
• Organisms living in lakes can die
– Greenhouse Effect: increasing carbon
dioxide (from burning fossil fuels) may cause
increases in global temperature
– Ozone Depletion: by CFC pollution (from
aerosol cans) increases our exposure to UV
radiation and increases rates of skin cancer
Use of Chemical
Pesticides & Herbicides:
– Chemicals that destroy
insects and weeds may
damage other wildlife
– Wash into the soil, go into
our air and water
food chain
– Ex: DDT
• Waste Disposal:
– Biodegradable vs. Nonbiodegradable Waste
• Do you know the difference?
– Plastic, metal cans, cardboard, paper,
electronics, chemicals, biological waste
Positive Improvements
• We are now recognizing the harm we are
doing to the environment and are taking
certain measure to help
• Population Control:
– encourage people to have fewer children
– birth control methods
Encourage Conservation of Resources:
– Conserve water, energy
– Reforestation
– Reduce, Reuse, Recycle
Establish Pollution Controls
– Use less fossil fuels
– Factories have filters on smokestacks
– Unleaded gasoline
– Recycling campaigns
Species Preservation:
– Limits on hunting and fishing
– Wildlife refuges, national parks
– Preserve habitat of endangered species
– Ex: Peregrine falcons, bald eagles
– Provide Nesting Sites
• Ex: Blue bird vs. Starling
– Special breeding programs
• Ex: Black footed ferrets
State Environmental Protection Laws:
– Hunting and fishing seasons and permits,
limits to size of catch
– Certain animals cannot be hunted
– Protection of breeding sites (ex: piping plover)
Use of Biological Controls to Control Pests:
– Use instead of spraying harmful chemicals in
– Introduce natural predator to help limit population of
• Wolves:
• Ladybugs and Praying Mantis:
– Sterilize individuals to prevent fertile mating of insects
– Use pheromones to lure and trap harmful insects
• Ex: Tse Tse Fly:
• Well…we thought it was a good idea…
• Cane Toad Disaster in Australia
Brought in to help eliminate insects that ate sugar cane
Skin contains a toxic poison that kill animals that try to eat it.
Population has now risen to epic proportions
Has endangered many other species (especially snakes)