Transcript Populations notes

What is a population?
Agenda for Monday Jan 30th
1. Populations notes
2. Population worksheet
• Why study populations?
– Learn how organisms change over time, problems in
an environment, and relationships between
organisms
– Population has group and not individual
characteristics
• Basic characteristics of a population:
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Density (no/area; no/vol)
Size (numbers)
Age Structure (based on age distribution)
Dispersion (the spread of individuals in relation to one
another)
What causes populations to
change?
1. Birth Rate
2. Death Rate
3. Number of individuals that enter and/or
leave
1. Immigration – into
2. Emigration – out
(Birth rate + immigration) – (death rate + emmigration)
Survivorship Curves
Exponential Growth Rate
• Ideal conditions
• More individuals = faster
growth
• Rarely happens
– WHY?
– Limiting factors
Logistical Growth Rate
• Populations go through
different growth phases
– Lag Phase – slow growth
– Exponential growth – rapid
growth, few die, many
reproduce
– Population growth slows
down
– Steady state – population
levels, birth rate = death rate
Carrying Capacity
• Maximum number of individuals that an
environment can support
– Measured in winter
Questions
• The human population is currently growing at
an exponential rate. What does this mean
about our birth and death rates?
• The Mantled Howler Monkey is currently
considered an endangered species. What does
this mean about its birth and death rates?
Population Density
• # of organisms per area
• Dispersion – pattern of spacing of populations
– 3 types
• Uniform
• Clumped
• Random
Dispersion Pattern: Uniform
Dispersion Pattern: Clumped
Dispersion Pattern: Random
Population Ranges
• Species are limited to where they may exist
• Abiotic conditions
Temperature
Rainfall
• Biotic conditions
Predators
Competitors
parasites
Humidity
Sunlight
Limiting Factors…
• Tolerance – ability of an organism to survive
when subjected to limiting factors
– Upper and lower limit = range
Density independent
factors
• affects the size of a population
regardless of the population density
– Abiotic
• Weather, Water, Fire, Sunlight, temperature
• Humans – dams, pollution
Density Dependent Factors
• A factor whose effects on the size or growth of
population vary with the population density
– Biotic factors
• Predation, disease/parasites, competition
• Food, water, shelter (resources)
Disease/Parasites
• Outbreaks of disease tend to occur when
population size has increased
– Disease is transmitted faster
– True for humans as well as animals
• Parasites increase at higher densities
Questions
Imagine a population of skunks. Imagine that the
skunks are reproducing at a very high rate, and the
skunk population is growing rapidly.
a) List a possible density-independent factor
that could stop the skunk population’s growth.
b) List a possible density-dependent factor
that would limit the skunk population’s growth.
Reproductive strategies
R-strategy (rate strategists)
• Reproduce quickly with many offspring
– Little energy in raising young
– Short life span
– Small in size
K-strategists (carrying capacity strategy)
• Few offspring
– Expend a lot of energy raising young
– Long life span
– Larger organisms
• https://www.youtube.com/watch?v=RBOsqm
BQBQk
Human Population Growth
http://www.census.gov/popclock/
• It took all of human history up to the early 1800s for
world population to reach 1 billion people
• until 1960 to reach 3 billion
• Today, the world gains 1 billion people every 11 years
• The current population is almost 8.5 times larger than
the population of 760 million at the beginning of the
Industrial Revolution
• At current growth rates, the world population could
double in as little as 58 years
What’s Behind Population Growth
• Animal Domestication
and Agriculture
– Provided for a few to feed
many
Leads to
Increased Fertility
Lower Infant Mortality
Increased Longevity
• Industrial Revolution
– Growth of Cities and
Infrastructure
• Water
• Energy
• Transportation
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Increased Productivity
Nutrition
Sanitation
Medicine
Human Carrying Capacity
•Technology has allowed us to raise Earth’s carrying
capacity
•Tool-making, agriculture, and industrialization each
enabled humans to sustain greater populations
• https://www.youtube.com/watch?v=ozDskXx
mdDI
• https://www.youtube.com/watch?v=VcSX4ytE
fcE
Human Population Growth
• Zero population growth
– birth rate + immigration rate = death rate +
emigration rate
• Age structure
– # of males and females in three age groups
• Pre-reproductive (0-19), reproductive (20-44), and
post –reproductive (45-80+)
Having many individuals in young age groups results in high
reproduction and rapid population growth
Why do some countries have a growing population
while other countries have a declining
population?
Male
Female
Expanding Rapidly
Guatemala
Nigeria
Saudi Arabia
Prereproductive ages
0–14
Male
Female
Expanding Slowly
United States
Australia
China
Reproductive ages
15–44
Male
Female
Stable
Japan
Italy
Greece
Postreproductive ages
45–85+
Male
Female
Declining
Germany
Bulgaria
Russia
Four Stages of Demographic
Transition
Water
consumption
Carbon emissions
Resource Consumption
Our ‘Commons’ are in Danger
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Atmospheric pollution and climate change
Water pollution, including ground aquifers
Deforestation and loss of oxygenation
The oceans, coral reefs and their bounty
National parks, wildernesses and wetlands
Nonrenewable natural resource depletion
– Fossil fuels, mineral ores, topsoil…..
Biodiversity is in Danger
• Humanity has spawned a species extinction to
rival the 5 great extinctions
– Recovery times took 10’s of millions of years
• Biodiversity is essential to life on Earth and
holds untold treasures for the future
• An ecological ethic is emerging
Concept Web
• write the “7 Billion People and Growing” in
the middle
• draw arrows to any of the other concepts that
form a cause and effect relationship
• Social, economic, envt impacts
• Positive, neutral, neg impacts on more people
Why do developing countries have a
growing population while developed
countries have a stable population?
Agenda for Friday Nov 4th
1. Population questions
2. Go over populations worksheet
3. Biodiversity
Quick Questions
1. What is a density independent factor?
1. List 1 example
2. What is a density dependent factor?
1. List 1 example
3. Why do populations rarely exhibit an exponential
growth rate?
4. When populations level out in logistical growth
rate, what is it called when they level out?
5. 5. A population is at carrying capacity. What does
that mean about its birth rates and death rates?
6. The Mantled Howler Monkey is currently
considered an endangered species. What does this
mean about its birth and death rates?
7. What are some limiting factors that would put a
population at its carrying capacity?
8. What type of growth are humans experiencing?
9. What major factors (3) have contributed to
human population growth?
10. What is a characteristic of an r-strategy
reproducing organism?