Population Ecology
and Ecosystems
Concepts and Applications: Chapters
40 & 43
Basic Concepts:
Chapters 27 & 30
http://darwin.bio.uci.edu/~sustain/bio65/lec16/b65lec16.htm
Population
Ecology
Ecology
Ecology: The study of how organisms
interact with one another and with their
environment
• Certain ecological principles govern the
growth and sustainability of all populations
• Human populations are no exception
Population
Ecology
Human Population Problems
• Over 6 billion people alive
• About 2 billion live in poverty
• Most resources are consumed by the
relatively few people in developed countries
Population
Ecology
Population
• A group of individuals of the same species
occupying a given area
• Can be described by demographics
– 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
clumped
• Crude density
information is more
useful if combined
with distribution data
nearly uniform
Fig 40.2
random
Population
Ecology
Determining Population Size
• Direct counts are most
accurate but seldom
feasible
• Can sample an area,
then extrapolate
• Capture-recapture
method is used for
mobile species
Mark and
Recapture
# marked Captured
Total Captured
= Number released
Total Pop
Population
Ecology
Assumptions in
Capture-Recapture
• Marking has no effect on mortality
• Marking has no effect on likelihood to being
captured
• There is no immigration or emigration
between sampling times
Population
Ecology
Changes in Population Size
• Immigration adds individuals
• Emigration subtracts individuals
• Births add individuals
• Deaths subtract individuals
Population
Ecology
Zero Population Growth- ZPG
• Interval in which number of births is balanced by
number of deaths
• Assume no change as a result of migration
• 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
Population
Ecology
r
• Net reproduction per individual per unit time
• Variable combines per capita birth and death
rates (assuming both constant)
• Can be used to calculate rate of growth of a
population
Population
Ecology
Exponential Growth Equation
G = rN
• G is population growth per unit time
• r is net reproduction per individual per unit
time
• N is population size
Population
Ecology
Biotic Potential
• Maximum rate of increase per individual
under ideal conditions
• Varies between species
• In nature, biotic potential is rarely reached
Population
Ecology
Limiting Factors
• Any essential resource
Space
that is in short supply
Food
• All limiting factors acting
Shelter
on a population dictate
Temperature
sustainable population
Mates
size
Pollution
Disease
Population
Ecology
Carrying Capacity (K)
• Maximum number of individuals that can be
sustained in a particular habitat
• Logistic growth occurs when population size
is limited by carrying capacity
Population
Ecology
Logistic Growth Equation
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
Population
Ecology
Logistic Growth
• As size of the
population increases,
rate of reproduction
decreases
• When the population
reaches carrying
capacity, population
growth ceases
carrying
capacity
Time
Population
Ecology
Overshooting Capacity
• Population may
temporarily increase
above carrying
capacity
• Overshoot is usually
followed by a crash;
dramatic increase in
deaths
Fig 40.7
Population
Ecology
Resetting the Carrying Capacity
• Major changes in environment can change
the carrying capacity of a local system
Fig 40.6
Population
Ecology
Density-Dependent Controls
• 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
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
Population
Ecology
Life Table
• Tracks age-specific patterns
• Population is divided into age categories
• Birth rates and mortality risks are calculated
for each age category
Population
Ecology
Survivorship Curves
Fig 40.8
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
Population
Ecology
Human Population Growth
1999
1975
domestication of
plants, animals 9000
B.C. (about 11,000
years ago)
agriculturally
based urban
societies
beginning of
industrial, scientific
revolutions
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
Population
Ecology
Resource Consumption
• 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
Population
Ecology
Effects of Economic Development
• 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
• World’s most extensive family planning
program
• Government rewards small family size,
penalizes larger families, provides free birth
control, abortion, sterilization
• Since 1972, TFR down to 1.8 from 5.7
Community
Ecology
Community Ecology
• 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
Community
Ecology
Types of Interactions
Who benefits?
•
•
•
•
•
•
Neutral
Commensalism
Mutualism
Competition
Predation
Parasitism
Spp 1
0
Y
Y
N
Y
Y
Spp 2
0
0
Y
N
N
N
Community
Ecology
Competition
• Competitive Exclusion
– Paramecium
• Resource Partitioning
– Fruit eating birds,
Barnacles
Community
Ecology
Predator-Prey Interactions
• The Classic Lynx / Hare system
Ecosystems
Ecosystems
• Energy is transferred from
the SUN to all organisms
• Primary Producers
• Consumers
• Decomposers
• Energy is LOST with each
transition
Ecosystems
Food Webs
MARSH HAWK
HIGHER
TROPHIC
LEVELS
Complex array
of carnivores,
omnivores and
other
consumers.
Many feed at
more than one
trophic level
continually,
seasonally, or
when an
opportunity
presents itself
CROW
UPLAND
SANDPIPER
GARTER SNAKE
FROG
SPIDER
SECOND
TROPHIC
LEVEL Primary
consumers
(e.g.,
herbivores)
FIRST TROPHIC
LEVEL
Primary
producers
• A composite picture
of an ecosystem’s
membership and
their interaction
WEASEL
CLAYCOLORED
SPARROW
EARTHWORMS, INSECTS (E.G.,
PRAIRIE VOLE
GRASSHOPPPERS,
CUTWORMS)
BADGER
POCKET
GOPHER
COYOTE
GROUND SQUIRREL
Fig. 43.6, p. 740
Do not post photos on Internet
Ecosystems
Food Webs can be Disrupted
• Natural Disasters
• External inputs
– Pesticides, Pollution
Ecosystems
ATMOSPERE
The Hydrologic Cycle
wind driven water vapor
40,000
evaporation
from ocean
425,000
precipitation
onto land
111,000
evaporation from land
plants
(evapotranspiration)
71,000
precipitation
into ocean
385,000
surface and
groundwater flow
40,000
LAND
OCEAN
Main
Reservoirs
Volume (103
cubic kiometers)
Oceans
1,370,000
Polar ice, glaciers
29,000
Groundwater
4,000
Lakes, rivers
230
Soil moisture
67
Atmosphere (water vapor)
14
Fig. 43.14, p. 746
Ecosystems
Other Cycles
• Carbon
• Nitrogen
• Phosphorus
Quiz