Population Ecology
Chapter 55
1
Environmental Challenge
• Ecology: the study of how organisms
interact with one another and their
environments.
• Populations: groups of individuals of the
same species in one place
2
Populations
• Range: area throughout which a population
occurs
– Most species have limited geographic range
• Devil’s hole pupfish lives in a single spring
in southern Nevada
3
Populations
• Humans alter
the
environment
and some
species have
altered their
range in
reponse.
Range expansion of the
cattle egret
4
Populations
• Dispersion: how individuals in a population
are spread out within their range
– Random: individuals do not interact
strongly with one another.
– Uniform: behavioral interactions,
resource competition
– Clumped: uneven distribution of
resources.
5
6
Biotic Potential
The rate of growth for a population if
every individual survived and
reproduced.
• Under such ideal conditions, a
population would have exponential
growth
Exponential growth = J-curve
b=d
Population
Growth levels off as
population approaches
carrying capacity
Exponential growth
initially
Lag phase
Logistic Growth
S-Curve
Growth and Limits
Many populations exhibit logistic growth
10
Carrying capacity (K): the maximum
number of individuals in a species that
an environment can support
• Determined by the amount of
resources available (food, water,
nutrients, etc)
• Results in logistic growth
• Hunting brings pop to Winter K
Demography and Dynamics
• Demography: the quantitative study of
populations
– How size changes through time
12
Population Changes
Calculating growth rates:
(Births + I) - (Deaths + E)
Immigrants (I) - Individuals moving into a
population
Emigrants (E) - Individuals moving out of a
population (exiting)
Limiting Factors: situations that prevent a
population from increasing
Density-Independent Factors
--do not depend on the number of
individuals in the population.
--Usually abiotic factors such as pollution,
weather events and natural disasters
Density-Dependent Factors
-become limiting only when population
reaches a certain size
-strongest when population is large
and dense
-usually biotic factors such as food,
predators, disease, and competition
Sawtooth Curve: Shows periodic
fluctuations (rise and fall) of
populations.
--Can show density-dependant factors
at work (predator-prey)
--Can show density-independent
factors at work (seasonal changes)
Sawtooth Graph
-showing seasonal population fluctuations
summer
winter
Fluctuations in the number of pupae of four
moth species in Germany
18
• North American snowshoe hare 10 year cycle
• Two factors generate this cycle:
– Food plants
– Predators
19
Reproductive patterns
1.r-strategist:
• produce many offspring in a short period
of time (mice, flies)
• take advantage of a temporarily abundant
resource
2.k-strategist:
• produce a few offspring that have a better
chance of surviving with intense parental
care (humans, elephants)
• Limited resources, pop near carrying
capacity
21
Human Population Growth
• K-selected life history traits
– Small brood size
– Late reproduction
– High degree of parental care
• Human populations have grown exponentially
– Last 300 years birth rate has remained same
– Death rate has fallen dramatically
22
Human population growth:
Year
Estimated population
(in millions)
0 A.D.
130
1650
500
1850
1,000 (1 billion)
1930
2,000
1970
4,000 (4 billion)
1998
6000
5/3/10
6,817,237,780
U.S. 309,191,081
A.The graph of human population is a J
curve. It shows exponential growth
Industrial
Revolution
begins
Agriculture
begins
Plowing
and
irrigation
Bubonic
plague
Number of years to add each billion (year)
All of Human History
First Billion
Second
Third
Fourth
123 (1930)
33 (1960)
15 (1975)
Fifth
12 (1987)
Sixth
12 (1999)
Seventh
Eighth
Ninth
(1800)
13 (2012)
16 (2028)
26 (2054)
Sources: First and second billion: Population Reference Bureau. Third through ninth billion: United Nations, World
Population in 2300 (medium scenario), 2003.
What has allowed human populations to
grow exponentially?
1.)medicine
2.)plenty of food(agriculture)
3.) sanitation
* medical advances allow people to live
longer and decreases infant mortality
(Child death)
C.What is Earths’ carrying capacity?
1. Unknown
2. J curve will continue until some
resource becomes limiting
3. Some countries have exceeded
their carrying capacities: China,
Ethiopia, Somalia, India
29
World Population Clock
Natural
Increase
per
Year
Day
Minute
More
Developed
Countries
World
Less
Developed
Countries
Less
Developed
Countries
(less China)
80,224,198
219,792
912,053
2,499
79,312,145
217,294
71,498,784
195,887
153
2
151
136
Source: Population Reference Bureau, 2004 World Population Data Sheet.
Human Population Growth
Distribution of population growth
31
Human Population Growth
• Consumption in the developed world
further depletes resources
– Wealthiest 20% of the world’s
population accounts for 86%
consumption of resources and
produces 53% of CO2 emissions
– Poorest countries: 20% is
responsible for 1.3% consumption
and 3% CO2 emissions
32
Human Population Growth
Ecological
Footprint:
amount of
productive land
required to support
an individual at the
standard of living
of a particular
population through
the course of
his/her life
33