Dispersal and Migration

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Dispersal and Migration

• How Populations Persist
• Chapter 11

Plants and animals when is it time to leave
home?
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Dispersal
Animals and plants my move from location to
location by active dispersal (migration), or by
passive dispersal (wind, water, or animal carrier)
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Dispersal may be the mechanism for persistence.

• Holyak and Lawler (1996)
• Populations of ciliates
• Colpidium stritum (prey)
• Didinium nasutum (predator)

Why?
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• The main problem affecting populations of is that
  they get too small and then disappear.
• If the habitat consists of connected
  microhabitats then migration and local
  extinction will become asynchronous

extinction gt
source gt

• Re-introduction will result in overall species
  persistence

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Carnivores and Home Range

• Bobcats are territorial and solitary.
• Each adult maintains home range. Bobcats of the
  same sex do not share the same home range (about
  20 Km2)
• Male home range sizes average 4900 acres (20 Km2
  or 8 miles 2)
• and female ranges average 2900 acres
• (12 Km2 or 4.5 miles 2)

Reference link
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Home range is proportional to energy needs

• Diet of the animal
• Carnivores work harder to find and capture food
  than do herbivores
• Size of the animal
• Big animals need more energy
• Distribution of the food resources
• If food is not uniformly distributed energy costs
  are high.

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For an organism, energy is proportional to size

• Energy aWb
• a to a basal metabolism constant
• b scale ratio base on increase with size
• W weight

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Dispersal How does migration take place?

• Monarch butterflies are known for southern
  migration they make every winter.
• from the northern U.S. and southern Canada (where
  they breed), to the lower part of California or
  the Sierra Madre mountains of Mexico

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Coriolis effect and the Ekman Flow
As surface water moves to the west, it causes low
pressure, and an upwelling The upwelling brings
high phosphorus levels supporting phytoplankton
growth
The coriolis effect produces a westward offshore
flow of water called the Ekman flow
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Ocean Currents Passive Dispersal

• Starfish begin life as tiny larvae, which are
  swept along for months by ocean currents -
  traveling many miles.

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Plant morphology passive dispersal

• Wind, water
• Dispersal of seeds, spores and pollen often
  depend on help from animal vectors
• Animals
• Dispersal of seeds, spores and pollen often
  depend on help from animal vectors

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Dormancy Traveling through Time

• One way species persist is by waiting for the
  good times.
• Dont you wish you could do this?

Local conditions my become non favorable, and the
organism can take a time out Dormancy may be
for days, weeks, months, and even years.
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Seed banks in nature

• Allows plants to disperse dormant offspring
  through space and time
• Germination may be triggered by a variety of
  environmental cues including fire.

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Primary Seed Dormancy

• Most seeds delay initial seed germination until
  favorable environmental conditions are present
• Physical seed coat dormancy The seed coat is
  prevents the uptake of water
• Mechanical dormancy, scarification (injury or
  chemical softening of the seed coat) must be
  accomplished prior to germination
• Chemical dormancy chemicals present within the
  seed coat inhibit germination. leaching by
  copious amounts of water over a period of time
  leads to germination.
• Morphological dormancy the embryo in the seed is
  immature. The seed must wait for a set with
  period of time with optimum conditions. 
• Environmental dormancy the seed requires some
  type of physiological condition to be met in
  order to germinate.  This might be dehydration,
  light exposure, or heat (fire)
• Deep dormancy The need to experienced a
  prolonged period of cold. During the first
  periods of warmth, seed will not germinate
  immediately until chilling one to three months of
  chilling temperatures have been experienced.

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The Evolution of Dormancy

• 91 of annual dormancy, compared to 52 of the
  perennials have dormancy.
• There appears to be a negative correlation
  between the longevity of the mature plant, and
  the longevity of seeds in the soil.
• Lilies and orchids are unique. Lilies require a
  double dormancy (two cold seasons), orchids
  require a fungal symbiont to trigger germination
• Reference Jonathan Silvertown 1999

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Where did my dormancy go?
Wild species are diploid with sexual
reproduction cultivated species are mostly
polyploid with vegetative propagation

• The end, or is it?
• Building a Better ---

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Torpor Intermittent dormancy
The badger will have awake times during the
winter but not that many of them All of this
means that the badger goes through torpor, or
temporary hibernation

• a time when the heartbeat, temperature, and body
  activities slow down. 

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Types of animal dormancy

• HIBERNATION Sleeping during the winter.
• TORPOR Shorter naps in cold conditions.
• ESTIVATION Sleeping the summer away.
• DIAPAUSE Deep sleeping through growing up.

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What makes a landscape fragmented?

• Metapopulation Research
• The study of the biology of species inhabiting
  fragmented landscapes

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Metapopulations

• Spatially discrete breeding populations
  (requires purposeful movement)
• All populations must have high risk of extinction
  so that at any time there exists some unoccupied
  habitat
• Movement for re-colonization is possible (The
  organism is not sessile or close to sessile)
• Asynchrony in local dynamics
• The network should contain a minimum of 20 well
  connected populations

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Genetics of populations

• The genetic equivalent of extinctions is loss of
  genetic variation
• The forces of genetic drift and migration work in
  opposite directions
• Drift eliminates genetic variation
• The smaller the population the faster the loss
  of variance
• Migration reintroduces genetic variation

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Evolution and equilibrium frequency
2pg(4Nm)/4(4Nm1)

• If migration and drift are in balance and an
  equilibrium level of heteroygosity will be
  reached

Gene flow into U.S. African American populations
are estimated to be between 20 to 30
percent (based on Rh factor and other alleles)