UNIT 2: ECOLOGY POPULATIONS

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UNIT 2 ECOLOGYPOPULATIONS

1. How Populations Grow
2. Limits to Growth
3. Human Population Growth

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1. How Populations Grow
Characteristics of Populations
Three important characteristics of a population
are Geographic Distribution Density Growth Rate
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Geographic Distribution (Range) the area
inhabited by a population
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Population Density the number of individuals
per unit area
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Population Growth
Populations can stay the same (), grow (), or
decrease (-) in size from year to year
Three factors can affect population size The
number of births The number of deaths The number
of individuals that enter or leave the population
Population Size of Births - of Deaths
Births (olive) Deaths (red) Population size (blue)
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Immigration the movement of individuals into an
area
Emigration the movement of individuals out of
an area
Which causes an increase in population size?
Decrease?
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Exponential Growth
Exponential Growth occurs when the individuals
in a population reproduce at a constant rate
Under ideal conditions with unlimited resources
J-shaped curve
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E. coli
Reproduce once/20 minutes
20 minutes 2
2n
40 minutes 4
n times reproduced
60 minutes 8
80 minutes 16 100 minutes 32 120 minutes
64 140 minutes 128 160 minutes 256 180
minutes 512 200 minutes 1024 220 minutes
2048 240 minutes 4096
4 hours?
5 hours 32,768 6 hours 262,144 8 hours
2,097,152
24 hours?
274
What if Unchecked?
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Logistic Growth
Logistic Growth occurs when a populations
growth slows or stops following a period of
exponential growth
What factors decrease? What factors increase?
Birthrate and Immigration
Death rate and Emigration
S-shaped Curve
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Carrying Capacity the largest number of
individuals (within a species) that a given
environment can support
More Natural
Growth rate equals zero
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2. Limits to Growth
Limiting Factors
Limiting Factor a factor that causes population
growth to decrease
Primary Productivity Limiting Nutrients
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Density-Dependent Factors
Density-Dependent Limiting Factor a limiting
factor that depend on population size
These factors operate most strongly when a
population is large and dense
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Competition
When populations become crowded, organisms
compete with one another for food, water,
space, sunlight, and other essentials
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Predator- Prey Relationship
Inverse relationship
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Parasitism
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Density-Independent Factors
Density-Independent Limiting Factors a limiting
factor that does not depend on the density of a
population
They affect all populations in similar ways,
regardless of the population size
Pop lt then gt
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Natural Disasters Human Disturbance
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3. HUMAN POPULATION GROWTH
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Historical Overview
Like the populations of many other living
organisms, the size of the human population
tends to increase with time
For most of human existence, the population grew
slowly
Life was harsh, and limiting factors kept
population sizes low
Food was scarce and diseases were rampant
Until fairly recently, only half the children in
the world survived to adulthood
Families would have many children to offset the
death rate
About 500 year ago, the human population began
growing more rapidly
Why?
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Agriculture and industry
Improved sanitation, medicine, and health
Death Rate? Birth Rate?
Experienced exponential growth
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1650 500 million 1850 (200 years) doubled ?
1 billion 1930 (80 years) doubled ? 2
billion 1975 (45 yeas) doubled ? 4
billion Today 6 billion
Increasing 80 million/year 214,000 people/day
Amarillo population Weekly San Antonio 3
years United States 2025 7.8 billion
Indefinite Growth?
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Limited Resources
The question is, when and how will our population
growth slow?
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Patterns of Population Growth
Demography the scientific study of human
populations
Examines the characteristics of human populations
and attempts to explain how those populations
will change over time
Examine birthrates, death rates, and the age
structure of a population
people per km²
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Over the past century, population growth in the
U.S., Japan, and much of Europe has slowed
dramatically (Developed Countries)
Hypothesis These countries have completed the
demographic transition
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Throughout most of history, human societies have
had high death rates and equally high birthrates
With advances in nutrition, sanitation, and
medicine, more children survive to adulthood and
more adults live to old age
These changes lower death rates and begin the
demographic transition
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Demographic Transition a dramatic change in
birth and death rates
BR DR
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Much of the population growth today is
contributed by only 10 countries, with India and
China in the lead, where birthrates remain high
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Age Structure
Age-Structure diagrams (Population Profiles)
graph the numbers of people in different age
groups in the population
Used to predict future growth
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Future Population Growth
Current projections suggest that by 2050, the
worlds population may reach more than 9 billion
people
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Most ecologists suggest that if this growth does
not slow down even more, there could be serious
damage to the environment as well as to the
global economy
On the other hand, many economists assert that
science, technology, and changes in society will
control those negative impacts on the environment
and economy