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Population Growth and
Human Influences on the Environment
What controls population growth?
• Three important characteristics in nature:
– 1. Geographic Distribution
• Range that describes the area inhabited by a population.
• Example: bacteria on a plate or whales in the Atlantic Ocean.
– 2. Density
• Number of individuals per unit area.
• Example: Low density, cacti in the desert.
– 3. Growth Rate
• Availability of food, survivorship and type of reproduction
• Example: Rabbits with lots of food, no predators and a high
reproductive rate will grow exponentially.
Population Growth
• Three factors affect population size…
– 1. Number of births.
• Populations grow if more individuals are born than die.
– 2. Number of deaths.
• Populations grow if fewer individuals die. Then there are more
adults to survive and reproduce.
– 3. Number of individuals entering and leaving the
population.
• Immigration – movement of individuals into an area (growth)
• Emigration – movement of individuals out of an area (shrink)
• Many reasons can cause individuals to move, like food
availability, mate choices, finding new territories, etc.
Types of Population growth:
Exponential
• If a population has
unlimited space and food
and no predators and
disease, the population will
increase exponentially.
• Occurs when individuals
reproduce at a constant
rate.
• As more individuals are
added to the population,
they also reproduce.
Types of Population Growth:
Logistic
The line at the top is called
the Carrying Capacity. This is
simply the largest number of
individuals that a given
environment can support.
• Logistic growth occurs
when a population’s
growth slows or stops
after exponential growth.
• Typically happens after
resources become less
available.
• Could be affected by
decrease in births,
increased death rates or
emigration.
Limits to growth
Density Dependent
• Limiting factor – factor that causes population
growth to decrease.
• 1. Density dependent limiting factor – based upon
population size
– Example: Competition, predation, parasitism or disease.
Limits to Growth
Density Independent
• 2. Density independent limiting factor – affects the
entire population regardless of size.
– Example: Extreme weather, seasonal cycles and human
activities
Human Population Growth
• Until 500 years ago with the advent of increased
agriculture, industry and medicine, human
population has increased dramatically.
• The only significant dip was the Bubonic Plague in
the 1300s C.E.
World Population
growth Rates.
It is projected that our
doubling time (the
amount of time
required for a
population to double in
size) is 61 years.
12 Billion by 2050!
As the world grows in people,
there are increased needs for
food, housing and services.
Demography
• Demography – study of human population.
• Birthrates, death rates, and age structures of
countries predict their population rates.
• Shown through graphs called age-sex pyramids.
To the left, a
country with little
growth (Denmark)
To the right, a
country with
massive growth
(Rwanda)
Demographic Transition Model
The demographic transition consists of four stages, which move from
high birth and death rates, to declines first in birth rates then in death rates,
and finally to a stage of low birth and death rates. Population growth is most
rapid in the second stage.
Future Human Population Growth
• Will human population reach it’s
carrying capacity?
• If population does not slow it will
dramatically hurt the environment and
the global economy.
• Ways to affect population growth
– Raising the status of girls & women
– Family Planning (Birth Control)
– Control of Disease (HIV, Ebola, etc)
– Education of Children (Literacy)
– Technology (agriculture, sustainable
living practices)
– Government policy (China)
Human Impacts on Resources and
Local Ecosystems
• Humans major affects on the biosphere:
– Hunting and Gathering (extinction of species,
introduction of non-native species, domestication)
– Agriculture (creates populations that do not move, use
up resources in an area, pesticides use, clear land for
crops)
– Industry (Pollution, Acid Rain, Greenhouse gases, Global
Warming, Biomagnification)
– Urbanization/Cities (Deforestation, Pollution, loss of
biodiversity of plants and animals, need for wildlife
products and loss of major Rainforests)
Biomagnification
• Biomagnification - is the bioaccumulation of a
substance up the food chain by transfer of residues of
the substance in smaller organisms that are food for
larger organisms in the chain.
• It generally refers to the sequence of processes that
results in higher concentrations in organisms at higher
levels in the food chain (at higher trophic levels).
• These processes result in an organism having higher
concentrations of a substance than is present in the
organism’s food.
• Examples: PCBs, DDT, Mercury, other heavy metals.
Rachel Carson
• Rachel Carson conservationist and the
worked to create environmental policy to
prevent environmental problems caused by
synthetic pesticides.
• The result was Silent Spring (1962), which
brought environmental concerns to the
public.
• Silent Spring spurred a reversal in national
pesticide policy—leading to a nationwide
ban on DDT and other pesticides—and the
grassroots environmental movement it
inspired the creation of the Environmental
Protection Agency (EPA).
The Future of Humankind:
Sustainability
• Use of alternative, renewable energy sources
– Examples: wind, solar, biofuels, reducing fossil fuel dependence
• Genetic engineering of agriculture and natural pest control
• Pollution controls
• Water conservation and purification
• Creation of Protected Wildlife Areas
• Forestry controls (replanting trees, protecting Rainforests)
• Regulation of Climate
– Example: reduction of Greenhouse gases and Ozone depleting
chemicals
• Sustainable housing (Energy, Water & materials)
• Reduce, Reuse and Recycle!