How Many Individuals Are IN a Population  (Births + Immigrants) - (Deaths + Emigrants) Lead to Population GrowthLead to Population Decline

We call these...  LIMITING FACTOR = Something that keeps a population from growing infinitely LIMITING FACTORS

There are 2 different models:  1. Exponential Growth Model  2. Logistical Growth Model

Exponential Growth  Resources are plentiful (there is a lot of food and water!)  All populations grow this way until some limiting factor stops them

Logistical Growth Model  Limiting factors keep the population from growing exponentially  Logistical growth = Carrying Capacity

Carrying Capacity  Carrying Capacity = highest number of organisms an area can hold  - This is where the Logistical Growth Model flattens out at the top

What determines the Carrying Capacity? LIMITING FACTORS!

What’s the Carrying Capacity Here?...  10,000 individuals = the highest number of individuals this area can hold

Human Population Growth  Just like all other organisms, human population all grow exponentially  Also, just like any ecosystem the Earth has a CARRYING CAPACITY. That is, there is a limit on the number of human beings that the Earth can support.  eature=related eature=related

World Carrying Capacity  At some point, human population will exceed Earth’s Carrying Capacity. When this happens, human population will have to decrease (i.e. people will die)  In fact, there is a lot of evidence that we are already getting very close to the Earth’s carrying capacity.

World Carrying Capacity In developed (rich) countries, humans are exceeding the Earth’s carrying capacity by consuming too many resources.

If Everyone Lived Like Americans If everyone lived like Americans, we would need eight Earths to provide all the food, water, and free space that we consume.

Human Carrying Capacity  In undeveloped (poor) countries, humans have exceeded their carrying capacity because there are too many people.  3.6 billion live in abject poverty (less than $2 per day)  Individually consume very few resources  But because there are billions of them, still exceed carrying capacity

What Does This Mean For Us? But wait! We just learned that when a population exceeds its carrying capacity, it shrinks in size (organisms die). If we’re exceeding our carrying capacity, why aren’t people dying?

 The sad truth is, people ARE dying. Someone dies of starvation every 2.43 seconds 2,200 people will die from starvation by the end of today’s class.

Leading cause of deaths worldwide Water pollution kills 14,000 people EVERY day

So What Do We Do? To avoid starvation, dehydration, and war for resources, we need to reduce consumption, reduce population growth, or both.  Four main strategies:  Voluntarily cut consumption  Find technological solutions to save resources  Birth Control, education, and women's rights in the third world  Planned birth policy

So What Do We Do? We could voluntarily cut down on our consumption.

So What Do We Do? Find technological solutions for using resources better. Norman Bourlag: The father of the Green Revolution, he is credited with saving more than 245 million lives. He invented new waves of growing crops in the developing world.

Political Policy We could try to discourage births by providing birth control... Education......and increasing women's rights in undeveloped countries, where birth rates are highest.

So What Do We Do? China has a planned birth policy: Since 1979, citizens have been limited to only one child per couple.