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Population
Ecology
Population Ecology
and Ecosystems
Ecology
Ecology: The study of how organisms
interact with one another and with their
environment
Concepts and Applications: Chapters
40 & 43
• Certain ecological principles govern the
growth and sustainability of all populations
• Human populations are no exception
Basic Concepts:
Chapters 27 & 30
http://darwin.bio.uci.edu/~sustain/bio65/lec16/b65lec16.htm
Population
Ecology
Human Population Problems
Population
Ecology
Population
• Over 6 billion people alive
• A group of individuals of the same species
occupying a given area
• About 2 billion live in poverty
• Can be described by demographics
• Most resources are consumed by the
relatively few people in developed countries
– Vital statistics such as size, density,
distribution, and age structure
Population
Ecology
Population Age Structure
• Divide population into age categories
• Population’s reproductive base includes
members of the reproductive and prereproductive age categories
Population
Ecology
Density & Distribution
• Number of
individuals in some
specified area of
habitat
• Crude density
information is more
useful if combined
with distribution data
Fig 40.2
1
Population
Ecology
Assumptions in
Capture-Recapture
Determining Population Size
• Direct counts are most
accurate but seldom
feasible
• Can sample an area,
then extrapolate
Mark and
Recapture
# marked Captured
Total Captured
Population
Ecology
• Marking has no effect on mortality
= Number released
Total Pop
• Marking has no effect on likelihood to being
captured
• There is no immigration or emigration
between sampling times
• Capture-recapture
method is used for
mobile species
Population
Ecology
Changes in Population Size
Population
Ecology
Zero Population Growth- ZPG
• Immigration adds individuals
• Interval in which number of births is balanced by
• Emigration subtracts individuals
number of deaths
• Births add individuals
• Assume no change as a result of migration
• Deaths subtract individuals
• Population size remains stable
Population
Ecology
Per Capita Rates
• Rates per individual
• Total number of events in a time interval
divided by the number of individuals
• Per capita birth rate per month =
Number of births per month
Population size
Population
Ecology
Exponential GrowthFig 40.4
• Population size
expands by ever
increasing increments
during successive
intervals
• The larger the
population gets, the
more individuals there
are to reproduce
2
Population
Ecology
Population
Ecology
r
Exponential Growth Equation
• Net reproduction per individual per unit time
G = rN
• Variable combines per capita birth and death
rates (assuming both constant)
• Can be used to calculate rate of growth of a
population
• G is population growth per unit time
• r is net reproduction per individual per unit
time
• N is population size
Population
Ecology
Population
Ecology
Biotic Potential
Limiting Factors
• Maximum rate of increase per individual
• Any essential resource
Space
under ideal conditions
that is in short supply
Food
• Varies between species
• All limiting factors acting
• In nature, biotic potential is rarely reached
Shelter
on a population dictate
Temperature
sustainable population
Mates
Pollution
size
Disease
Population
Ecology
Carrying Capacity (K)
Population
Ecology
Logistic Growth Equation
• Maximum number of individuals that can be
sustained in a particular habitat
• Logistic growth occurs when population size
is limited by carrying capacity
G = rmax N (K-N/K)
• G = population growth per unit time
• rmax = maximum population growth rate per
unit time
• N = number of individuals
• K = carrying capacity
3
Population
Ecology
Logistic Growth
Population
Ecology
Overshooting Capacity
• As size of the
population increases,
rate of reproduction
decreases
• Population may
temporarily increase
above carrying
capacity
• When the population
reaches carrying
capacity, population
growth ceases
• Overshoot is usually
followed by a crash;
dramatic increase in
deaths
Fig 40.7
Population
Ecology
Resetting the Carrying Capacity
Population
Ecology
Density-Dependent Controls
• Major changes in environment can change
the carrying capacity of a local system
• Logistic growth equation deals with
density-dependent controls
• Limiting factors become more intense as
population size increases
• Disease, competition, parasites, toxic
effects of waste products
Fig 40.6
Population
Ecology
Density-Independent Controls
• Factors unaffected by population density
• Natural disasters or climate changes affect
large and small populations alike
Population
Ecology
Life History Patterns
• Patterns of timing of reproduction
and survivorship
• Vary among species
• Summarized in survivorship curves
and life tables
4
Population
Ecology
Population
Ecology
Life Table
Survivorship Curves
• Tracks age-specific patterns
• Population is divided into age categories
• Birth rates and mortality risks are calculated
for each age category
Fig 40.8
Population
Ecology
Human Population Growth
Population
Ecology
Human Population Growth
• Population now exceeds 6 billion
• Rates of increase vary among countries
• Average annual increase is 1.26 percent
• Population continues to increase exponentially
Fig. 40.9, p. 695
Population
Ecology
How Humans have Side-Stepped
density dependent controls
• Expanded into new habitats
• Agriculture increased carrying capacity; use
of fossil fuels aided increase
• Hygiene and medicine lessened effects of
density-dependent controls
Population
Ecology
Future Growth
• Exponential growth cannot
continue forever
• Breakthroughs in
technology may further
increase carrying capacity
• Eventually, densitydependent factors will slow
growth
Population
Momentum
• Lowering fertility rates
cannot immediately slow
population growth rate.
Why?
• If every couple had just
two children, population
would still keep growing
for another 60 years
5
Population
Ecology
Resource Consumption
Population
Ecology
Effects of Economic Development
• United States has 4.7 percent of the world’s
population
• Americans have a disproportionately large
effect on the world’s resources
• Per capita, Americans consume more
resources and create more pollution than
citizens of less developed nations
• Total fertility rates (TFRs) are highest in
developing countries, lowest in developed
countries
• When individuals are economically secure,
they are under less pressure to have large
families
Population
Ecology
Slowing Growth in China
Community
Ecology
Community Ecology
• World’s most extensive family planning
program
• Government rewards small family size,
penalizes larger families, provides free birth
• Community: Populations of all species in a
habitat.
• Niche: Sum total of all a species activities
and relationships as species do what they do.
– Fundamental, Realized
control, abortion, sterilization
• Since 1972, TFR down to 1.8 from 5.7
Community
Ecology
Types of Interactions
Community
Ecology
Competition
Who benefits?
•
•
•
•
•
•
Neutral
Commensalism
Mutualism
Competition
Predation
Parasitism
Spp 1
0
Y
Y
N
Y
Y
Spp 2
0
0
Y
N
N
N
• Competitive Exclusion
– Paramecium
• Resource Partitioning
– Fruit eating birds,
Barnacles
6
Community
Ecology
Predator-Prey Interactions
Ecosystems
Ecosystems
• The Classic Lynx / Hare system
• Energy is transferred from
the SUN to all organisms
• Primary Producers
• Consumers
• Decomposers
• Energy is LOST with each
transition
Ecosystems
Food Webs
Ecosystems
Food Webs can be Disrupted
• A composite picture
of an ecosystem’s
membership and
their interaction
• Natural Disasters
• External inputs
– Pesticides, Pollution
Do not post photos on Internet
Fig. 43.6, p. 740
Ecosystems
Ecosystems
Other Cycles
• Carbon
• Nitrogen
• Phosphorus
The Hydrologic Cycle
Fig. 43.14, p. 746
7
Quiz
8