Chapter 5
Populations
5-1 How Populations Grow
• I. Characteristics of Populations
– A. geographic distribution- or range
describes the area inhabited by a population
(ex. Few cubic centimeters of apple (bacteria) to
millions of square kilometers of Pacific Ocean
(whales)
– B. population density- number of individuals
per unit area (ex. Tall saguaro cactuses and
smaller desert plants)
– C. population growth- affected by number of
births, deaths, and individuals entering and
leaving population
• immigration and emigration (ex. Otters/sea urchins/kelp/killer
whales)
– D. age structure- youth in a population is going to
predict a more rapid growth (ex. US population vs.
Rwanda population)
• II. Exponential growth
A. If a pop. has abundant space and food and
is protected from predators and disease- the
pop. size will increase indefinitely
B. Occurs when a population grows at a
constant rate- starts slow then grows quickly
C. Called a J-shaped curve
• III. Logistic Growth
• A. When resources become less available the
growth slows or stops
• B. The population reaches the carrying
capacity which is the number of organisms
that the particular environment can support
• C. Called a S-shaped curve
5-2 Limits to Growth
• Limiting factor- something that causes the population
to decrease
• I. Density-dependent limiting factors
– A. Competition- when populations get crowded
organisms compete for:
•
•
•
•
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1. food
2. water
3. space
4. sunlight
5. other essentials
Density Dependent Limiting Factors
– B. predation- ex. Chart of wolf and moose (p. 126)
– C. parasitism and disease- like predators,
parasites take nourishment often weakening and
cause death (ex. Cordyceps fungus that infects
insects)
II. Density-independent limiting factors
– A. Unusual weather- tornados, hurricanes
– B. Natural disasters- fire, rain
– C. Seasonal cycles- frost, drought
– D. Human activities- damming rivers, clearing forest
5-3 Human Population Growth
• Human Population- Dot Video
• A. The human population cannot keep growing
forever because the earth and its resources are
limited
• B. Demography- study of human populations
– 1. With advances in nutrition, sanitation and
medicine more children survive and adults live
longer
– 2. As societies modernize, increase level of
education, and raise their standard of living, families
have fewer children
– 3. Demographic transition has occurred in the
U.S., Europe, and Japan
– 4. Much of today’s population occurs in 10
countries with India and China in the lead
Questions
• 1.Why is the overall growth rate low in
stage 1?
• 2. Why does the growth rate rise
dramatically in stage 2?
• 3. At which stage are the US, Canada,
and Japan?
Computer based projection of what may happen if human population size
continues to skyrocket without dramatic policy changes and technological
innovation.
6-1 A Changing Landscape
• Human Influences
– Hunting and gathering, agriculture, industry and
urban development have all affected the natural
activities of ecosystems around the world
• Agriculture
– The practice of farming and raising domesticated
animals for food
– Monoculture- growing the same crop on a large
plot year after year
– Green Revolution- the effort to develop larger
quantities and better quality crops to feed growing
population
• Industrial Growth and Urban Development
– Industrial Revolution in the 1800s- machines
and factories led to the modern life we know
– Many of our activities now need energy to
power our machines which uses fossil fuelscoal, oil, and natural gas
6-2 Renewable and
Nonrenewable Resources
• Tragedy of the Commons
• I. Classifying Resources
– Renewable Resources- can be regenerated
or replenished by natural cycles• These can still be overused and become limited
• Ex. Trees, fish, water, soil
– Nonrenewable Resources- cannot be
regenerated and once used are gone forever
• Ex. Coal, oil and natural gas
• II. Sustainable Development
– A way of using natural resources without
depleting them or causing long term
environmental harm
– Takes into consideration how the natural
ecosystem functions as well as how the
human economic system operates
• III. Land Resources
A. If used properly, land is a renewable
resource.
B. Soil erosion-increased by plowing
C. Desertification-turning once productive areas
into deserts by farming, overgrazing, and
drought
Forest Resources
• Whether a forest can be considered a
renewable resource depends partly on the
type of forest (temperate forests grow
quickly, but old-growth forests are
essentially non-renewable). The oldest
recorded age of a California redwood is
over 2200 years!
• Deforestation-leads to: erosion, changes
to local soil
Air Resources
• Pollutants
• Acid rain-burning of fossil fuels releases
nitrogen and sulfur compounds into
atmosphere, where they combine with
water vapor to form nitric acid and sulfuric
acid
Biodiversity
• One of Earth’s greatest natural resources
• Many different species have provided us with food,
industrial products, and medicines such as antibiotics,
painkillers, heart drugs, antidepressants, and anticancer
drugs.
• Threats to biodiversity:
– Altering habitats
– Hunting species to extinction
– Introducing toxic compounds into food webs
– Introducing foreign species to new environments
Chapter 6 (pg 152) Pollution
• Biological magnification- concentrations of a
harmful substance that increase in organisms at
a higher trophic levels
• DDT pesticide problem
– Cheap, long activity, kills many types of insects,
controls pests and mosquitoes
– Hazardous: nonbiodegradable and organisms don’t
eliminate it from their bodies
– The pesticide remains in tissues of plants and
passed to the herbivores and omnivores
– Top predator fish-eating birds were affected the
most, causing thin eggs shells and death of
offspring and the threatening of their populations
• DDT was banned in most industrialized
countries in the early 1970’s.
• Since then the populations of many birds,
including the bald eagle, have recovered
significantly.
6.4 The Future
• Ozone layer-limits our exposure to
damaging UV rays from the sun, which
can cause cancer, damage eyes, and
decrease resistance to disease.
• In 1974 it was shown that chlorofluorocarbons, or CFCs, could damage the
ozone layer.
• CFCs were banned for use as propellants
in aerosol cans, and the levels of chlorine
in the atmosphere are falling.
• Global climate change is a concern:
– Global warming is the increase in the Earth’s
average temperature range. 1998 was the
warmest year since record-keeping began.
– Is global warming a result of a larger, natural
cycle or human actions?
– Carbon dioxide levels have risen for the past
200 years, so the natural greenhouse effect
has been intensified.
– Recent models suggest that by 2050 the
average global surface temperature will
increase by 1 to 2 degrees Celsius.
• Possible Effects of global warming:
– 1. flooding of coastal areas
– 2. some areas will see more droughts
– 3. new organisms may live in areas where
they once could not, or some may not be able
to live where they once did.