Z333 Lecture

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Introduction to Ecology
What is Ecology?
Answer The study of inter-relationships among
living things and the non-living
environment
Abiotic Non-living factors
Biotic Living factors
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Introduction to Ecology
Ecology - Increasing Levels of Complexity
Population All members of a particular species
living within a defined area
Biosphere Earth (multiple ecosystems)
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Chapter 38 Population Growth Regulation
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Chapter 38 Population Growth Regulation
Influences Affecting Population Sizes

• 1) Births
• 2) Deaths
• 3) Migration
• Immigration migration into a population
• Emigration migration out of a population

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Chapter 38 Population Growth Regulation
Ultimate size of population balance between
opposing forces
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Chapter 38 Population Growth Regulation
Biotic potential can produce Exponential Growth

• Continuously accelerating increase in
  population size

Growth Rate Measure of ? in population size /
time
Growth Rate (r) Birth Rate (b) - Death Rate
(d)
1500 / 10,000
- 500 / 10,000
(10)
- 0.05 deaths / person / year
0.10 increase / person / year
0.15 births / person / year
Population Growth of individuals added to
population / time
Population Growth Growth Rate (r) x
Population Size (N)
0.10 increase / person / year
x 10,000 People
1000 new individuals / year
New Population Size 11,000
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Chapter 38 Population Growth Regulation
Biotic potential can produce Exponential Growth
New Population Size 11,000
2nd year 0.10 x 11000 1100 3rd year
0.10 x 12100 1210 4th year 0.10 x
13310 1331 5th year 0.10 x 14641
1464

• J curve

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Chapter 38 Population Growth Regulation
Factors Affecting Biotic Potential
1) Age at which organism first reproduces (? age
? rate)
2) Frequency with which reproduction occurs (?
freq. ? rate) 3) Average number of
offspring / event (? ? rate) 4) Length of
organisms life span (? lifespan ? rate) 5)
Death rate of individuals (ideal condition - ?
rate ? rate)
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Chapter 38 Population Growth Regulation
Exponential growth cannot continue indefinitely
Boom-and-Bust Cycles Rapid population growth
followed
by massive die-off (short-lived organisms)
(Environmental Resistance Predominates)
(Biotic Potential Predominates)
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Chapter 38 Population Growth Regulation
Exponential growth cannot continue indefinitely
Boom-and-Bust Cycles Rapid population growth
followed
by massive die-off (short-lived organisms)
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Chapter 38 Population Growth Regulation
Environmental resistance stabilizes population
growth for many long-lived organisms (no
boom-bust cycles)

• S-curve

Carrying Capacity The maximum population size
that an ecosystem can support
indefinitely
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Chapter 38 Population Growth Regulation
Carrying Capacity Determined By

• 1) Renewable Resources ? Nutrients, water,
  light
• Replenished by natural processes (can be
  damaged)
• 2) Non-renewable Resource ? Space

Factors of Environmental Resistance Maintaining
Populations At / Near Carrying Capacity
1) Density-Independent Factors Limit pop. size
regardless of pop. density
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Chapter 38 Population Growth Regulation
Factors of Environmental Resistance Maintaining
Populations At / Near Carrying Capacity
2) Density-dependent Factors Factors more
effective as population size increases
Most Important

• More abundant prey more chance of meeting
• predator

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Chapter 38 Population Growth Regulation
Factors of Environmental Resistance Maintaining
Populations At / Near Carrying Capacity
2) Density-dependent Factors Factors more
effective as population size increases
b) Parasitism One organism (parasite) feeds
off another organism (host) without
killing it

• More abundant hosts easier for parasite to
  find

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Chapter 38 Population Growth Regulation
Factors of Environmental Resistance Maintaining
Populations At / Near Carrying Capacity
2) Density-dependent Factors Factors more
effective as population size increases
c) Competition Organisms compete among each
other for limited
resources (e.g. food)

• Two types of competition
• 1) Interspecific Competition between species
• 2) Intraspecific Competition within species

More Intense
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Chapter 38 Population Growth Regulation
Populations Exhibit Differing Spatial
Distributions
Distribution Spatial pattern in which
population members are
arranged in given area.
Types of Spatial Distribution
1) Clumped Population members live in defined
groups
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Chapter 38 Population Growth Regulation
Populations Exhibit Differing Spatial
Distributions
Distribution Spatial pattern in which
population members are
arranged in given area.
Types of Spatial Distribution
2) Uniform Relative constant distance between
population members
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Chapter 38 Population Growth Regulation
Populations Exhibit Differing Spatial
Distributions
Distribution Spatial pattern in which
population members are
arranged in given area.
Types of Spatial Distribution
3) Random Members scattered haphazardly across
landscape

• Very rare in animals

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Chapter 38 Population Growth Regulation
Populations Show Characteristic Patterns of
Survivorship
Survivorship Curve Graph depicting of
individuals in an age class against their age

• Low infant death rates
• Produce few offspring

• Constant death rate
• Produce variable offspring

• High infant death rates
• Produce many offspring

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Chapter 38 Population Growth Regulation
So How Do Humans Fit Into This?
More hospitable environment
More efficient food gathering
? death rates
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Chapter 38 Population Growth Regulation
Doubling Time
70 / growth rate ()
70 / 1.4 50 years
70 / 0.6 117 years
(Figure 38.13)
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Chapter 38 Population Growth Regulation
The human population will stop its exponential
growth either we will voluntarily reduce our
birth rate, or various forces of environmental
resistance will dramatically increase our
death rates the choice is ours...
- Earth Watch (pg. 809)