Population Dynamics

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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 nations beekeepers
watched in horror as more than a quarter of their
2.4 million colonies collapsed, killing billions
of natures little fertilizers.
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Outline

• 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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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.
• lt1 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 S 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 non-overlapping
  generations, can estimate growth rate.
• Geometric Rate of Increase (?)
• ?N t1 / Nt
• N t1 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 S 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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