1. D2.3
Changing Populations

2. Overgrowth in Human Populations
Recall, sustainability is:
the ability for a population (or ecosystem) to be maintained at a certain rate or level, by also ensures the availability of resources in the future.
If a human population grows beyond its capacity, it will experience problems such as:
overcrowding
outbreaks in disease
water, food and housing shortages
pollution and waste accumulation

3. Overgrowth in Human Populations
New Delhi, capital of India
Ottawa, capital of Canada
Pop India: 1,170,938,000 in 3,287,590 km² = 356 ppl/km2 vs. Pop Canada: 34,108,752 in 9,984,670 km² = 3.50 ppl/km2

4. Growth Rates The two main growth rate patterns are:
Exponential growth
Logistic Growth
population growth at an increasingly rapid rate in proportion to the total population size.
Logistic (or constant) growth
population growth that is continuously growing and decreasing over time, as a result of balance within the population.

5. Growth Rates
Bacteria are an example of a population that grows exponentially
Bacteria are single-celled organisms that reproduce by splitting in two.
the doubling time is the amount of time it takes for a population to double in size
For bacteria that happens in one generation. For populations that DO NOT grow exponentially it takes considerably longer.
2  4
4 8

6. Growth Rates
a population that experiences exponential growth will continue to grow at a faster and faster rate.
for these populations, growth will continue until a limiting factor slows or stops the population’s expansion
in the Ancient Rome example; limiting factors were disease, lack of clean water, food and shelter.
for bacteria; limiting factors would be lack of food, increase in temperature and presence of toxin (antibiotics)

7. Please copy the completed graph into your notes
Growth Rates
a population that experiences exponential growth will continue to grow at a faster and faster rate.
When exponential growth is graphed, the shape of the line is like the letter “J”
thus, these graphs are also referred to as J-curves
Please copy the completed graph into your notes

8. Factors that Support Exponential Growth
species that are able to grow exponentially:
have short life spans
reproduce often
produce numerous offspring
do little to care for young

9. Factors that Support Exponential Growth
exponential growth can only occur in some organisms, under ideal conditions
most often seen in
micro-organisms (e.g. bacteria)
small animals (e.g. insects)
certain plants (e.g. weeds)

10. Factors that Limit Exponential Growth
Scarcity of resources, such as:
food
water
living space / shelter
availability of mates
Predation
Disease

11. Population Explosions & Crashes
a population explosion is a sudden exponential growth in a population
…so the explosions are usually followed a population crash: a rapid drop in population size
most ecosystems cannot tolerate exponential population growth for very long…
Please copy the completed graph into your notes
This is generally due to the limiting factors in the ecosystem, acting on the population.

12. Factors affecting populations
Most populations experience logistic growth,
by definition, these populations fluctuate in size, in responses to environmental conditions:
Factors that increase population size
births
immigration (movement into the population)

13. Factors affecting populations
Most populations experience logistic growth,
by definition, these populations fluctuate in size, in responses to environmental conditions:
Factors that decrease population size
deaths
emigration (movement out of the population)
If all four of these factors can occur in a population, it is called an open population.
If conditions prevent immigration and emigration, the population is said to be closed

14. Equilibrium Carrying Capacity
the carrying capacity of a population is the maximum number of individuals that can be sustained in an ecosystem
While some populations will alternate between explosions and crashes, most will find an equilibrium

15. Carrying Capacity
the curve for a population that is being limited by its carrying capacity is called an S-curve

16. Human Population Growth
explosive growth of the human population is linked with advancements in agriculture, industry, science/medicine
specifically the Industrial Revolution of the 18th century
living conditions improve (better hygiene linked with higher education)
death rate lowered due to advancements in medicine
for most of its history, the human population has been stable or grown very slowly

17. Human Population Growth
the 21st century is the first time in the world’s history that the elderly will out number the youth
the carrying capacity of the Earth depends on:
food and resource supply
waste disposal
pollution
access to clean water
distribution of populations

18. Human Population Growth
The current population of the world is about 7,237,851,917 (~7 billion)
growing at an annual rate of 1.7%, will add approximately 93 million people / year
The carrying capacity of the Earth is estimated to be around ~12 billion
If the human population growth continues at its current rate of growth, scientists estimate it will reach the earth’s carrying capacity in ~ 53 years
Recall the term “sustainability”
The human population is NOT currently growing in a sustainable way.

19. Human Population Growth
Recall the term “sustainability”
Will the the human population be an S-curve…
…or a J-curve?

20. Assignment: PRACTICE PROBLEMS # 7, 8, 10 & 11 (pg 484) 18-22 (pg 485)
2.3 Summary Q. 5
(pg 487)