1. Populations & Humans in the Biosphere
Chapter 5 & 6
Populations
&
Humans in the Biosphere

2. Copyright Pearson Prentice Hall
Chapter 5 Populations
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3. Videos Black-Footed Ferrets http://youtu.be/LkoCNnV7RFY
Quest Video KQED: What’s killing the sea otters
Sea Otters and Kelp
The science of overpopulation youtube
7 billion; how did we get so big so fast youtube
2012 wolf population on Isle Royale youtube
Black-Footed Ferrets

4. What shapes an ecosystem?
The Niche
Competition
Exponential growth
Logistic growth
Carrying Capacity
Limiting Factors

5. 5-1 How Populations Grow
Four Important Characteristics of a Population
Geographic distribution: the area inhabited
Population density: the number of individuals per unit area = # 𝑜𝑓 𝑖𝑛𝑑𝑖𝑣𝑖𝑑𝑢𝑎𝑙𝑠 𝑎𝑟𝑒𝑎
Growth rate: change in number of individuals over time
The population’s age structure.

6. Exponential Growth
Under ideal conditions with unlimited resources & protection from predators & disease, a population will grow exponentially = the biotic potential of a species.
Individuals in a population reproduce at a constant rate.
Population reaches an infinitely large size.
Characterized by a J shaped curve.

7. Exponential Population Growth

8. Logistic Growth
In nature, exponential growth does not continue in a population for very long.
A population's growth slows or stops following a period of exponential growth
The environment reaches its carrying capacity
1. As resources become less available, the growth of a population slows or stops.
2. When birthrate decreases, death rate increases.
3. When immigration decreases, emigration increases

9. Logistic growth is characterized by an S-shaped curve.

10. Carrying Capacity
The largest number of individuals that a given environment can support.
When a population reaches the carrying capacity of its environment, its
The growth levels off.
The average growth rate is zero.
Stop and practice

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5-2 Limits to Growth
Limiting Factors
The primary productivity of an ecosystem can be reduced when there is an insufficient supply of a particular nutrient.
Ecologists call such substances limiting nutrients.
A limiting nutrient is an example of a limiting factor.
In the context of populations, a limiting factor causes population growth to decrease.
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12. Density-Dependent Limiting Factors
Depend on population size.
Become limiting if population reaches a certain size; generally LARGE & DENSE, not scattered and small
Include:
Competition
Predation
Parasitism
Disease

13. Density-Dependent Factors: Competition
Crowded populations of the same species compete for food, water, space, sunlight
Competition can also occur between members of different species.
Both species will be under pressure to change in ways that reduce competition
This type of competition can lead to evolutionary change.
Over time, the species may evolve to occupy different niches.
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14. Density-Dependent Factors: Predation
Populations in nature are often controlled by predation.
The regulation of a population by predation takes place within a predator-prey relationship.
Example: A small population of wolves controls the size of a large population of moose.

15. The gray wolf and moose population of Michigan’s Isle Royale
Isle Royale is a small, isolated and remote, forested island in Lake Superior 
It is uninhabited by humans except for 155 campsite permits each summer
There is little migration of animals onto the island
Here scientists conduct the longest continuous study of a predator-prey system in the world

16. Density-Dependent Factors-Predation
Wolf and Moose Populations on Isle Royale
The relationship between moose and wolves on Isle Royale illustrates how predation can affect population growth. In this example, the moose population was also affected by changes in food supply, and the wolf population was also affected by disease.
Moose Wolves
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17. The predator-prey cycle
Periodic increases in the moose population are quickly followed by increases in the wolf population
More wolves results in increased predation
This causes moose population to decline
Since there are fewer prey the wolf population declines also

18. Density-Dependent Factors: Parasitism and Disease
The moose population on Isle Royale is affected by a parasite
The wolf population on Isle Royale is affected by a virus introduced by a camper’s dog

19. Should humans intervene?
Rolf Peterson, the longest-serving director of wolf-moose studies on Isle Royale, argued for this view in an op-ed he coauthored for the New York Times:
“The future health of Isle Royale will be judged against one of the most important findings in conservation science: that a healthy ecosystem depends critically on the presence of top predators like wolves when large herbivores, like moose, are present. Without top predators, prey tend to become overabundant and decimate plants and trees that many species of birds, mammals and insects depend on.”
- See more at:

20. Density-independent limiting factors
Affect all populations in similar ways, regardless of the population size.
Examples:
unusual weather like drought or hurricanes
natural disasters
seasonal cycles
certain human activities—such as damming rivers and clear-cutting forests

21. 5-3 Human Population Growth Historical Overview
With advances in sanitation, agriculture, industry and medicine, the human population experienced exponential growth.

22. Demography is the study of populations
Demography helps to explain the patterns of population growth and decline
Birthrates, death rates, and the age structure help predict the growth rate of countries
Globally, the growth rate hit a peak in the 60’s at around 2%
The current growth rate is around 1%.
Although declining, any value above zero means that population continues to grow.
It is expected to reach 9 billion by 2050.

23. Patterns of Population Growth
U.S. Population
In the United States, there are nearly equal numbers of people in each age group.
This age structure diagram predicts a slow but steady growth rate for the near future.
80+
Males
Females
60–64
Age (years)
40–44
This graph shows the age structure of the U.S. population.
20–24
0–4
Percentage of Population
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24. Patterns of Population Growth
Rwandan Population
In Rwanda, there are many more young children than teenagers, and many more teenagers than adults.
This age structure diagram predicts a population that will double in about 30 years.
80+
Males
Females
60–64
Age (years)
40–44
This graph shows the age structure of the Rwandan population.
20–24
0–4
Percentage of Population
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25. The Demographic Transition
Over the past century, population growth in the United States, Japan, and much of Europe has slowed dramatically.
According to demographers, these countries have completed the demographic transition, a dramatic change in birth and death rates.

26. Three Stages of Demographic Transition
Stage 1: both rates high
Stage 2: death rate drops birth rate high = population increases
Stage 3: birth rate drops and population growth slows

27. Patterns of Population Growth
The demographic transition is complete when the birthrate falls to meet the death rate, and population growth stops.
Birthrates, death rates, and the age structure of a population help predict the rate of population growth. Birthrates and death rates fall during the demographic transition. In Stage I, both the birthrate and death rate are high. During Stage II, the death rate drops while the birthrate remains high. Finally, in Stage III, the birthrate also decreases.
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