Chapter 8
Population Change
Overview of Chapter 8
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Principles of Population Ecology
Reproductive Strategies
The Human Population
Demographics of Countries
Demographics of United States
Principles of Population Ecology
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Population Ecology
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Study of populations and why their numbers
change over time
Important for
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Endangered species
Invasive species
Population
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Group of individuals of same species living in
the same geographic area at the same time
Population Density
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Population density
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The number of individuals of a species per unit
area or volume at a given time
Ex: minnows per Liter of pond water
Ovals below have same population, and
different densities
Change in Population Size
Change in Population Size
Calculating Population Change
Growth
rate
Death
rate
Emigration
rate
r = (b – d) + (i – e)
Birth
rate
Immigration
rate
Birth (b), Death (d), Immigration (i) and Emigration
(e) are calculated per 1000 people
Maximum Population Growth
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Intrinsic Rate of Growth (Biotic Potential)
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Growth rate under ideal conditions
J- Shaped Curve (exponential growth)
Environmental Resistance
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Environmental limits (resistance)
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Prevent indefinite reproduction
Unfavorable food, water, shelter, predation, etc.
Carrying Capacity (K)
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Maximum # of individuals an environment can
support
Causes leveling off of exponential growth
S- shaped curve of logistic population growth
Population Crash
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Overshooting carrying capacity can lead to
population crash
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Abrupt decline in population density
Factors That Affect Population Size
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Density Dependent Factor
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Factor whose effect on population changes as
population density changes
Examples:
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Predation
Disease
Competition
Sometimes cause Boom-or-Bust Population
Cycles
Boom-Or-Bust Population Cycles
Case Study- Predator Prey Dynamics on
Isle Royale
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As wolf population increases, moose
population decreases (and vice versa)
Factors That Affect Population Size
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Density Independent Factors
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Factors that affects population size, but is not
influenced by changes in population density
Examples:
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Killing frost
Severe blizzard
Fire
Reproductive Strategies
r-selected species
k-selected species
-Small body size
-Small broods
- Early maturity
-Long life span
- Short life span
-Slow development
- Large broods
-Large body size
- Little or no parental
-Late reproduction
care
-Low reproductive rate
- Probability of long term -Redwood trees and
survival is low
human beings
- Mosquitoes and
Dandelions
Survivorship
Some populations fit two curves
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Herring Gulls
Type III &
Type II
Human Population
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Demography
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Science of
population structure
and growth
Human Population
since 1980 is Jshaped curve
Human Population
1 Billion
1800
2 Billion
1930
3 Billion
1960
4 Billion
1975
5 Billion
1987
6 Billion
1999
6.6 Billion
2006
Population Increase in Mexico
Projecting Future
Populations
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Population is increasing
Growth rate (r) has
started to decline
Projections for 2050
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Low = 7.7 billion
High = 10.6 billion
Most likely = 9.1 billion
Demographics of Countries
Demographic Stages
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Pre-industrial Stage
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Transitional Stage
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Lowered death rate
Rapid population growth
Industrial Stage
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Birth and death rates high
Modest population growth
Birth rate decline
Population growth slow
Post Industrial Stage
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Low birth and death rates
Population growth very slow
Demographic Stages
Age Structure
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The number and proportion of people at
each age in a population
Demographics of Specific Countries
World-wide
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29% of human
population is under
age 15
Could cause large
increase in birth
rates
Education of Immigrants into US
The Role of Education in Society