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Population Dynamics
Chapter 10
Honeybees pollinate one-third of the fruits, nuts and vegetables
that end up in our homey kitchen baskets.
Fall 2006- the nation’s beekeepers watched in horror as more
than a quarter of their 2.4 million colonies collapsed, killing
billions of nature’s little fertilizers.
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Outline
• Dispersal
– In Response to Climate Change
– In Response to Changing Food Supply
– In Rivers and Streams
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Metapopulations
Estimating Patterns of Survival
Survivorship Curves
Age Distribution
Rates of Population Change
– Overlapping Generations
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dispersal
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Dispersal
• 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
Mourning Dove (left) with Eurasian
Collared-Dove (right). Photo by Marie
Weinstein, Alabaster, AL.
• 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
• 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
• 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
• 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
• 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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Estimating Patterns of Survival
• 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
• 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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Fig. 10.13
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Fig. 10.14
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Survivorship Curves
• 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
• 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
• 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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Fig. 10.20
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Dynamic Population in a
Variable Climate
• 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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Fig. 10.21a
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Fig. 10.21b
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Rates of Population Change
• 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
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
• 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
• 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
• Dispersal
– In Response to Climate Change
– In Response to Changing Food Supply
– In Rivers and Streams
•
•
•
•
•
Metapopulations
Estimating Patterns of Survival
Survivorship Curves
Age Distribution
Rates of Population Change
– Overlapping Generations
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