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POPULATION ECOLOGY
Introduction
• Population = group of individuals of a single
species living in same general area
• Density: # individuals / area
• Dispersion: pattern of spacing between individuals
Patterns of Dispersal:
1. Clumped – most common; near
required resource
2. Uniform – usually antagonistic
interactions
3. Random – not common in
nature
• Survivorship curves plot the proportion of
individuals alive at each age
• Three types of survivorship curves reflect
important species differences in life history
Figure 35.6
Evolution shapes life histories
• An organism's life history is the series of events
from birth through reproduction to death
• Life history traits include
•
•
•
•
•
the age at which reproduction first occurs
the frequency of reproduction
the number of offspring
the amount of parental care given
the energy cost of reproduction
Life History: traits that affect an organism’s
schedule of reproduction and survival
3 Variables:
1. Age of sexual maturation
2. How often organism reproduces
3. # offspring during each event
Note: These traits are evolutionary outcomes, not conscious
decisions by organisms
How do populations grow?
• Idealized models describe two kinds of population
growth
1. exponential growth
2. logistic growth
1. Exponential population growth: ideal conditions,
population grows rapidly
2. Logistic growth is slowed by population-limiting
factors
K = Carrying capacity is
the maximum
population size
that an environment
can support
Unlimited resources are
rare
Figure 35.3B
Laboratory Populations
Factors that limit population growth:
• Density-Dependent factors: population matters
• i.e. Predation, disease, competition, territoriality,
waste accumulation, physiological factors, no food
left
• Density-Independent factors: population not a factor
• i.e. Natural disasters: fire, flood, weather
• Populations fluctuate due to biotic and abiotic
factors
1975-1980: peak in wolf numbers
1995: harsh winter weather (deep snow)
Boom-and-bust cycles
• Predator-prey interactions
• Eg. lynx and snowshoe hare on 10-year cycle
The Spread of Shakespeare's Starlings
• In 1890, a group of Shakespeare enthusiasts
released about 120 starlings in New York's Central
Park
Today: over 100 million starlings, spread over N. Amer.
We can draw parallels to what is happening with the human population…
THE HUMAN POPULATION
• doubled three times
in the last three
centuries
• about 6.1 billion and
may reach 9.3 billion
by the year 2050
• improved health and
technology have
lowered death rates
• The ecological footprint represents the amount of
productive land needed to support a nation’s
resource needs
• The ecological
capacity of the world
may already be
smaller than its
ecological footprint
Per capita CO2 emissions
(metric tons of carbon)
0
1
2
3
U.S.
China
5
6
5.48
2.65
Japan
2.51
0.29
0
0.5
1
U.S.
Russia
Japan
India
1.5
1.49
China
0.75
Russia
India
4
Total CO2 emissions
(billion metric tons of carbon)
0.91
0.39
0.32
0.28