Population Dynamics
Chapter 14: Population Ecology
• Read the blurb about zebra mussels p.g.
646.
• As a group (and with your teacher’s help)
work through the questions below.
Characteristics of Populations
• Population size
– Number of individuals of a species occupying
a given area at a given time
• Population density (D)
D=N
S
N: Total number of individuals
S: Space occupied by the population
• Small organisms usually have higher
population densities than larger organisms
Characteristics of Populations-cont’d
• Crude density
– Population density measured in terms of the
number of organisms of the same species
within a habitat’s total area
• Ecological density
– Population density measured in terms of the
number of organisms of the same species
within the area actually used by those
organisms (ex. land animals do not live in
lakes)
1.) Complete worksheet on calculating
population density.
2.) Worksheet #1 in population ecology
packet
3.) a.) Design your own question (with
diagram) for pop. Density
b.) Crude and ecological densities
c.) share with classmates
Characteristics of Populations-cont’d
• Population dispersion patterns (fig. 4,
page 652)
– Clumped dispersion (ex. schools of fish)
– Uniform dispersion (ex. King penguins)
Rarely found in nature
– Random dispersion (ex. rainforest trees)
• 1st half of page 2 in population ecology
handout.
Characteristics of Populations-cont’d
• Often, impractical to count exact numbers
of a population
– Count a sample and then estimate total size
– Sampling techniques:
• Quadrat sampling
• Mark-recapture method
• Technological tracking devices
Characteristics of Populations-cont’d
• Quadrat sampling
– Used for stationary or small organisms (ex.
plants, insects)
– A quadrat (ex. 1m2) is used and a sample of
populations is counted within that area.
– Population size and density can be
extrapolated for the entire area based on that
quadrat’s data.
1.) Worksheet on Quadrant sampling
2.)“Too Many to Count” activity with a group
3.) Page 2 – 3 (quadrant sampling) in
population ecology packet.
Characteristics of Populations-cont’d
• Mark-Recapture Method
– for mobile wildlife.
– sample captured, marked and then released
– Marked animals mix randomly with unmarked
animals and then a second sample of animals
is captured
• Marked to unmarked animals can be used to
estimate the size of the entire population.
Characteristics of Populationscont’d
• Mark-Recapture Method-cont’d
M=m
N n
M = Total # marked
N = Total population
m = # of recaptures
n = Size of 2nd sample
Ex.) on p.g. 655
http://www.biologycorner.com/flash/mark_recap.swf
• Mark and recapture worksheet.
Characteristics of Populations-cont’d
• Technological Tracking Devices
– When capturing animals for estimating
population size, researchers may also attach
radio collars, satellite-linked devices or other
technological equipment
• Used to track migration and/or behaviour patterns
• Information can be mapped in geographic
information systems (GIS)
• Must ensure these devices do not harm the
animals or restrict their activities
• Complete pages 3 & 4 in your Population
ecology packet.
Measuring and Modeling
Population Change
• Carrying capacity
– The maximum number of organisms that can
be sustained by available resources over a
given period of time
Measuring and Modeling
Population Change
• Population dynamics
– Changes in population characteristics determined by
natality, mortality, immigration and emigration
• Fecundity
– The potential for a species to produce offspring in one
lifetime (ex. high fecundity-starfish; low fecundityhumans)
Measuring and Modeling
Population Change
• Biotic potential
– The maximum rate a population can increase
under ideal conditions
Population change =
[(births + immigration)-(deaths + emigration)] x 100
initial population size (n)
Measuring and Modeling
Population Change
• Open population
– Size and density influenced by births, deaths, immigration
and emigration
• Closed population
– Size and density Influenced by births and deaths only
– No migration occurs
Measuring and Modeling
Population Change
• Three general survivorship patterns of species:
Type I: High survivorship until fairly late in life, then high mortality
Typically produce small numbers of offspring
Type II: A fairly constant death rate
Type III: Low survivorship early in life (ex. green sea turtles)
Typically produce large numbers of offspring
• Complete page 5 in your Ecology Packet.
• Try out the calculating populations
worksheet using the formulae they provide
for you.
Measuring and Modeling
Population Change
• Geometric growth
• Population grows rapidly during breeding season
then declines throughout the rest of the year until
the next breeding season
– Growth rate is a constant from year to year
but not during the year
Measuring and Modeling
Population Change
• Geometric growth-cont’d
• Read pages 662-664 and complete
page 6 in population ecology packet.
Measuring and Modeling
Population Change
• Exponential Growth
– Doubling time is a constant value
– Populations exhibiting this growth increase in
numbers rapidly
– Results in a J-shaped growth curve
– Although the overall graph appears similar to
geometric growth (J-shape), in this case, there are no
fluctuations (jumps) as a result of breeding times
Measuring and Modeling
Population Change
• Exponential growth-cont’d
• Read P.g. 664-665 and complete the
corresponding part on p.g. 7 in Population
ecology packet
Measuring and Modeling
Population Change
• Logistic Growth
– Most common growth pattern seen in nature
– Geometric and exponential models assume
that a population will grow indefinitely at the
same rate
• Realistically, limiting factors limit population growth
and the population reaches the ecosystem’s
carrying capacity
• At the carrying capacity, the number of births and
the number of deaths become equal
Measuring and Modeling
Population Change
Logistic Growth-cont’d
Measuring and Modeling
Population Change
• Logistic Growth
– S-shaped (sigmoidal) curve
– Three distinct phases:
• Lag phase: Population is small and increasing
slowly
• Log phase: Population undergoes very rapid
growth.
• Stationary phase: Population growth slows / stops
• Read pages 666- 669 and complete page
7 -8 in population ecology packet.