What kind of plants do we see in a
climax community?
Agenda for Tuesday Jan 27th
1. Population Notes
• Why study populations?
– Learn how organisms change over time, problems in
an environment, and relationships between
organisms
Population Growth Rate
• Must know birthrate and mortality
• Emigration – moving out of a pop.
• Immigration – moving into a pop.
– Immigration rate = emigration rate
• Calculating growth rate
=(population at end – population at beginning)
Population at beginning
Exponential Growth Rate
• Occurs when organisms have
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
Steady
state
Slows
Lag
Exponential
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?
Carrying Capacity
• Maximum number of individuals that an
environment can support
– Measured in winter
Limiting Factors…
• Anything that prevents the number,
reproduction, distribution, growth of an
organism
– Abiotic
– Biotic
• Tolerance – ability of an organism to survive
when subjected to limiting factors
– Upper and lower limit = range
Population Ranges
• Species are limited to where they may exist
• Abiotic conditions
Temperature
Rainfall
• Biotic conditions
Predators
Competitors
parasites
Humidity
Sunlight
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.
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
Reproductive strategies
R-strategy (rate strategists)
• Produce as many offspring as possible in a short
time
– Little energy in raising young
K-strategists (carrying capacity strategy)
• Few offspring that have a better chance of living
– Expend a lot of energy raising young
Compare and contrast r and k
reproductive strategies
Agenda for Wednesday Jan 28th
1. Invasive species project
Quiz tomorrow
What is a density independent factor?
A density dependent factor?
Agenda for Thursday Jan 29th
1. Go over HW
2. Quiz
3. Human populations
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
Human Population Growth
What’s Behind Population Growth
• Three Factors
– Fertility
– Infant Mortality
– Longevity
• Animal Domestication
and Agriculture
– Provided for a few to feed
many
• Industrial Revolution
– Growth of Cities and
Infrastructure
• Water
• Energy
• Transportation
–
–
–
–
Increased Productivity
Nutrition
Sanitation
Medicine
Resource Consumption (6)
• High
consumption
• Getting worse
• Rate increase
faster than
population
growth
Human Carrying Capacity
•Technology has allowed us to raise Earth’s carrying
capacity for our species time and again.
•Tool-making, agriculture, and industrialization each
enabled humans to sustain greater populations.
Our ‘Commons’ are in Danger
•
•
•
•
•
•
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 of 65 - 440 million
years ago
• Recovery times from the great extinctions
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
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+)
Why do some countries have a growing population
while other countries have a declining
population?
Concept Web
• Social, economic, envt
• Positive, neutral, neg impacts on more people
What event in human history
helped spark our population
growth?
Agenda for Friday jan 31st
1. Quiz
2. Present
What concerns are there about the
increase in human population?
Agenda for Monday Feb 3rd
1. Present
2. Biomes