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What can limit population?

What can limit population?


Jan 29 Notes

What can limit population?

Topic: I. Systems

A. Definition - A set of components that function together as one

ex: Human Body, Car, The Jungle, Radio, the Planet Earth

Depends on the multiple interactions

#1 Brederton Illustration - a simplified diagram of the Earth’s Systems

B. Feedbacks

#1 Positive Feedback - Not sustainable

Something will break, overheated to a certain time

Can be dangerous - destabalize a system

We like exponential growth in our bank account for compound interest ( there is not enough money in the world... it is limited)

People don’t like it in terms of the population and disease

#2 Negative Feedback -

Stabalizes the system

C. Examples

Why did so many women die in their 20s in rome?

If you want to learn more check out Is culture a uniquely human product?

Negative Feedback

Skiiers who have never gone to a path others have gone

The more people are there, the less they want to go

Positive Feedback

The slopes get better and the skiers want to go where the people are

Negative Feedback:

Going to the grocery lane with the least number of people to get the transaction done faster Positive Feedback

Two nightclubs

It can breakdown ... things change... people think it is overcrowded and leave the place

Negative Feedback

DMS = clouds and sunlight

Vehicular traffic - Rush hour traffic, the more there are the less I want to go there D. Combined Feedback Don't forget about the age old question of In a monohybrid cross of plants where tall is dominant and short is recessive, what are the odds of getting 4 short, recessive plants?
We also discuss several other topics like How is rate obtained?

ex: Network of Feedbacks in the Amazon

What is the top cause of death from 1900 to 1998?

E. ***Daisyworld Example

Black like it cool but make it warm

White like it warm but make it cool

Black and White Daisies = It comes to an equilibrium where people

Albedo- brightness of surface - friction lf light reflected

=>Daisyworld goes to different phases in the heating of the SUN

Starts with black daisies in the middle - too cold for the white daisies

White start to pop up in the middle

White start overwhelming the middle of the planet while black daisies go to the poles It gets too hot even for the white daisies and the system breaks

II. Environmental Unity

A change in one part of the system affecrs the other components


Sea Otters (fishermen killed them because they thought it was just eating their fish - once the otters were dead the sea urchins grew in population - urchin killed the kelp - lost of the fish babies habitat - the sea otters were sustaining the system)

The fishermen only saw one part of the system - they caused bigger problems by taking away a key organism

Flight Delays (one delay causes more floghts to be delayed)

B. Example

Sembolisi National Park

Insight - The initial assumptions were limited and not comprehensive of the overall problem If you want to learn more check out What is rate law?

C. Polar Ice and Temperature Example

Desertification in Desert

*Was once a living ecosystem

Sunlight became less due to Orbital Variations - vegetation & ecosystem

Insolation - Amount of solar energy that comes to the ground

*Retrodicted - 5400 years ago - The Sahara transformed from a woodland to a desert Positive Feedback & Negative Feedback breaks down

Ex: Urban City

D. Uniformitarianism

“The present is the key to the past”

Underlying premise - the system is dominated by day-to-day functions

The daily functions control the behavior of the system

ex: The Beach

Wind, Sea, Sand

E. Catastrophism


view that the system is dominated by sudden and sometimes devastating events Ex: Beach is dominated by the storm

Insight: Both are correct

Robustness of a systems - day-to-day restores itself after a catastrophic event Catastrophes can be traced

Differentiation of Resistance ( the ability to not be devestated) & Resiliance (the ability to restore after a devetation)

Catastrophe - Major Fires

Uniformatarianis. -


STOCK - the total amount ofsomething Don't forget about the age old question of What measures the total income of everyone in the economy?

FLUX - the rate at which something enters/leaves a system


Resilience Time

Example - Growing the Lehigh population by 1000 students

Input is much more than the output - the reservoir is going to grow

Other examples

Beach Sand, Conveyor Belts, Earth’s Radiation

Tropical Forests, Fish, Lobsters, Mineral Ores, Ground Water, CO2, population A. water in a damned reservoir

Residence Time - Volume/Outflow

Derive: How to get Time? Stuff/Stuff/Time

Stock(Stuff)/ Flux (Stuff/Time) We also discuss several other topics like What is the difference between magma and lava?

B. Exponential Growth

*Discussion on the formula

Important Distinction = Scientific Growth rate IS DIFFERENT from the discreet compunding interest from Business

The more you have, the faster you get more...

Doubling Time Approximation= 70/k


IV. Nonlinearities in the EARTH SYSTEM & Challenges

Coevolution of Earth & Life

Major Events

Photosynthesis: Oxygen

Land Plants: Less CO2

Humans : Perturbations

*Gaia Hypothesis

*Life has not done it in purpose

Metaphor - System and a bank account

Humans have been eating out of the principal of the the earth’s goods and services

Jan 31

Topic: Population

I. Population Insights:

There have been about 50 billion since Homo Sapiens - about 300,000 years ago 7.7 billion people are alive now

*Human Population is the biggest challenge in environmental challenges

Ex: the spike would be called an infection/plague

Growth Area is reflected in the age of the population

Rapid growth in Kenya

Slow Growth in the US

Zero growth/Decrease in Italy

1-child policy in China

*Explosion of the Population in AFRICA compared to that of Asia

II. Example in the US about Immigration

If immigration and fertility do not change, the population will exponentially increase Perhaps taking it back to 1492... where the US population grew

South and the West are growing while the East is declining in terms of population due to the shift in industry

*Focus on being careful with the data


Fertility = # of babies born to each woman in their lifetime

Constant Fertility = 2.5

slow Fertility reduction = 2.1

Fast Fertility reduction. =1.6

IV. Demographic Transition

Time lag between having the security of having kids live and of changing parents perspectives Death rate declines first, then the # of children being born decreases

# OF PEOPLE will be in Asia and Africa

*Babies cost money

Rich people can afford more babies, but poorer people have more babies



*Eliminate Poverty

*Stabilize climate

*Protect marginalized communities

What can limit population?




How do people die?

Change in the top cause of death from 1900 to 1998

From tuberculosis and lung related disease to heart related diseases and cancer

*Old people had a better chance in ancient Rome more than in modern England?

Why did so many women die in their 20s in Rome?

Childbirth caused such death

Cesarean procedures caused the child to live but the mom to die

V. Carrying Capacity of the Earth... how do you want to live?

2.5 billion if people ate like Americans

40 billion if people ate just to survive and the lands were farmed intensely we can’t tell others you should do this... that is not science

A. Population Collapse

B. You have increasing population even with decreasing fertility rate

Why? Because of then

*Fertility rate depends on the education of women

Education during the thick of child-bearing years

The later you start, the less you have

In some cultures it is different (ex: Israel)

Men control the household

Women’s value is the number of children they bear for their husbands

*For a significant portion of history

China and India houses the most in terms lf the world’s population

World Population video - from 1 Ad

Roman Empire

Golden Age of India

Mayan Empire

Rise of Islam

Viking Conquests - North Europe

Crusades - more people on Europe

Mongols in China - Death in China

Black Plague - Death in Europe

New World

Colonial America

Industrial Age

in 2000 years - the last 100 increased the population immensely World War

Modern Medicine

Information Age

*Population will double in 50 years

Slowing population growth &

Professor when he was in grade school --- 3 billion 7.7 billion people

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