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Population Dynamics
Chapter 10
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Outline
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Dispersal
 In Response to Climate Change
 In Response to Changing Food Supply
 In Rivers and Streams
Metapopulations
Patterns of Survival
Survivorship Curves
Age Distribution
Rates of Population Change
 Overlapping Generations
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Dispersal
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Africanized Honeybees
 Honeybees (Apis melifera) evolved in
Africa and Europe and have since
differentiated into many locally adapted
subspecies.
 Africanized honeybees disperse much
faster than European honeybees.
 Within 30 years they occupied most
of South America, Mexico, and all of
Central America.
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Africanized Honeybees
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Collared Doves
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Collared Doves, Streptopelia decaocto,
spread from Turkey into Europe after 1900.
 Dispersal began suddenly.
 Not influenced by humans.
 Took place in small jumps.
 45 km/yr
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Collared Doves
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Rapid Changes in Response to Climate Change
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Organisms began to spread northward about
16,000 years ago following retreat of glaciers
and warming climate.
 Evidence found in preserved pollen in lake
sediments.
 Movement rate 100 - 400 m/yr.
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Rapid Changes in Response to Climate Change
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Dispersal in Response to Changing Food Supply
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Holling observed numerical responses to
increased prey availability.
 Increased prey density led to increased
density of predators.
 Individuals move into new areas in
response to higher prey densities.
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Dispersal in Rivers and Streams
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Stream dwellers have mechanisms to allow
them to maintain their stream position.
 Streamlined bodies
 Bottom-dwelling
 Adhesion to surfaces
Tend to get washed downstream in spates.
 Muller hypothesized populations
maintained via dynamic interplay between
downstream and upstream dispersal.
 Colonization cycle
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Dispersal in Rivers and Streams
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Metapopulations
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A metapopulation is made up of a group of
subpopulations living on patches of habitat
connected by an exchange of individuals.
 Alpine Butterfly - Roland et al.
 Lesser Kestrels - Serrano and Tella.
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Patterns of Survival
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Three main methods of estimation:
 Cohort life table
 Identify individuals born at same time
and keep records from birth.
 Static life table
 Record age at death of individuals.
 Age distribution
 Calculate difference in proportion of
individuals in each age class.
 Assumes differences from mortality.
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High Survival Among the Young
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Murie collected Dall Sheep skulls, Ovis dalli.
 Major Assumption: Proportion of skulls in
each age class represented typical
proportion of individuals dying at that age.
 Reasonable given sample size of 608.
 Constructed survivorship curve.
 Discovered bi-modal mortality.
 <1 yr.
 9-13 yrs.
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Survivorship Curves
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Type I: Majority of mortality occurs among
older individuals.
 Dall Sheep
Type II: Constant rate of survival throughout
lifetime.
 American Robins
Type III: High mortality among young,
followed by high survivorship.
 Sea Turtles
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Survivorship Curves
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Age Distribution
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Age distribution of a population reflects its
history of survival, reproduction, and growth
potential.
Miller published data on age distribution of
white oak (Quercus alba).
 Determined relationship between age and
trunk diameter.
 Age distribution biased towards young
trees.
 Sufficient reproduction for replacement.
 Stable population
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Age Distribution
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Age Distribution
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Rio Grande Cottonwood populations
(Populus deltoides wislizenii) are declining.
 Old trees not being replaced.
 Reproduction depends on seasonal
floods.
 Prepare seed bed.
 Keep nursery areas moist.
 Because floods are absent, there are now
fewer germination areas.
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Dynamic Population in a Variable Climate
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Grant and Grant studied Galapagos Finches.
 Drought in 1977 resulted in no recruitment.
 Gap in age distribution.
 Additional droughts in 1984 and 1985.
 Reproductive output driven by
exceptional year in 1983.
 Responsiveness of population age
structure to environmental variation.
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Rates of Population Change
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Birth Rate: Number of young born per
female.
Fecundity Schedule: Tabulation of birth rates
for females of different ages.
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Estimating Rates for an Annual Plant
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P. drummondii
 Ro = Net reproductive rate; Average
number of seeds produced by an individual
in a population during its lifetime.
 Ro= Σ lxmx
 X= Age interval in days.
 lx = % pop. surviving to each age (x).
 mx= Average number seeds produced by
each individual in each age category.
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Estimating Rates for an Annual Plant
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Because P. drummondii has nonoverlapping generations, can estimate
growth rate.
 Geometric Rate of Increase (λ):
 λ=N t+1 / Nt
 N t+1 = Size of population at future time.
 Nt = Size of population at some earlier
time.
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Estimating Rates when Generations Overlap
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Common Mud Turtle (K. subrubrum)
 About half turtles nest each year.
 Average generation time:
T = Σ xlxmx / Ro
 X= Age in years
 Per Capita Rate of Increase:
r = ln Ro / T
 ln = Base natural logarithms
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Review
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Dispersal
 In Response to Climate Change
 In Response to Changing Food Supply
 In Rivers and Streams
Metapopulations
Patterns of Survival
Survivorship Curves
Age Distribution
Rates of Population Change
 Overlapping Generations
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