Chapters 5 & 6
Populations & Humans in the Biosphere
5-1
How Populations Grow
Characteristics of Populations:
1. Geographic Distribution- describes
The area inhabited by a population
2. Density- the number of individuals per
Unit area
3. Growth Rate- rate in which a
population changes (+, 0, or -)
4. Age-Structure
Population Growth: 3 Factors
IF:
1. Number of births
2. Number of deaths
3. Number of individuals that enter or
leave the population
Birthrate > Death rate = increase in pop. Size
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Birthrate = Death rate = Pop. stays about the same
Birthrate < Death rate = Decrease in pop. size
Immigration- The movement of individuals into an area
Emigration- The movement of individuals out of an area
Exponential Growth: (J-shaped)(Fig. 5-3)
-It occurs when the individuals in a population
reproduce at a constant rate. (No limits)
Logistic Growth: (S-shaped)(Fig. 5-4)
- It occurs when a population’s growth slows or
stops following a period of exponential growth.
(Growth with limits)
Carrying Capacity- the largest number of
individuals that a given environment
can support over time.
5-2 Limits to Growth
Limiting Factors- is a factor that causes population
growth to decrease.
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Density-Dependent Factors:
-Factors that depend on population size
Examples:
1. Competition- When populations become
crowded, organisms compete
with each other for food, water,
space, sunlight, etc.
2. Predation- The regulation of a population
takes place within a predator-prey
relationship.
3. Parasitism and Disease- Parasites can also
limit the growth of a
population.
Density-Independent Factors:
-Factors that affect all populations in similar
ways, regardless of the population size.
Examples:
1. Unusual weather-drought, heavy rains.
2. Natural Disasters- hurricanes, tornados
3. Certain human activities- clear cutting forests
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5-3 Human Population Growth
Historical Overview:
-For most of human existence, the population
grew slowly. (Food was scarce, diseases.)
-Not long ago, only ½ the children in the world
survived to adulthood.
-About 500 years ago, the human population
began growing more rapidly. Agriculture and
industry made this possible.
Patterns of Population Growth:
Demography – the scientific study of human
populations.
Birthrates, death rates and the age-structure of a
population help predict why some countries have high
growth rates while others grow more slowly.
Demographic Transition- a dramatic change in birth and
death rates.
Stage I= both birth rate and death rate are high
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Stage II= the death rate drops but the birth rate
remains high.
Stage III= both birth and death rates drop.
Age Structure Diagrams- Show the population of a
country broken down by
gender and age group.
(Fig. 5-13)
Future Population Growth:
-Current projections suggest that by 2050, the world
population may reach 9 billion people.
-By 2050 the growth may level off or even decrease.
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Chapter 6
Humans in the Biosphere
6-3 Biodiversity
Biodiversity- Is the sum total of the genetically based
variety of all organisms in the biosphere.
Ecosystem Diversity- Includes the variety of habitats,
communities and ecological
processes in the living world.
Species Diversity- Refers to the number of different
species in the biosphere.
Genetic Diversity- Refers to the sum total of all the
different forms of genetic
information carried by all organisms
living on Earth today.
Threats to Biodiversity:
-Human activities like; altering habitat,
overhunting, introducing toxic compounds into
food webs and introducing foreign species to
new environments can reduce biodiversity.
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Biological Magnification- Concentrations of a harmful
substance increase in
organisms at higher trophic
levels in a food chain or web.
(Fig. 6-16)
Conserving Biodiversity:
Conservation- Is used to describe the wise management
of natural resources, including the
preservation of habitats and wildlife.
6-4 Charting a Course for the Future
Ozone Depletion:
Ozone Layer- between 20-50 kilometers above
Earth’s surface, the atmosphere
contains a relatively high
concentration of ozone gas. Ozone
consists of 3 O2 atoms.
-Ozone layer functions as an absorbent of
harmful ultraviolet (UV) radiation from
sunlight before it reaches the Earth’s surface.
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-Think of it as a global sunscreen.
Early Evidence:
-In the 1970’s a scientist found evidence from
satellite data that a hole in the ozone layer over
Antarctic exited during the winter.
-Since then it has grown larger and a similar ozone
hole also appeared over the Arctic.
The Cause:
-In the mid 1970’s scientists published that CFC’s
could damage the ozone
Solution:
-Reduce CFC usage!!! Today, most uses of CFC’s are
banned
**Current data shows that the ozone holes should shrink
and disappear within 50 years.
Global Climate Change:
-Scientists are concerned about the strong evidence
that the climate is changing.
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-Since the late nineteenth century, the average
atmospheric temperature’s on Earth’s surface have
risen about 0.6 degrees C. (About 0.2-0.3 since
1980!!!)
Global Warming- The term used to describe this
increase in the average temperature of
the biosphere.
**New Term:
Global Change- Is the new term because not all
places are actually warming.
Evidence of Global Warming:
-The most widely accepted hypothesis is that
current warming is related to human activities that
are adding CO2 other greenhouse gases to the
atmosphere, thus causing the atmosphere to retain
more heat.
Possible Effects of Global Warming:
-Sea levels may rise enough to flood some coastal
areas. Social and economic consequences.
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-Some parts of North America may experience more
droughts during the growing season.
-New organisms may live where they once could not.
-Other organisms may become threatened or extinct
in area where they once lived.
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