Dispersal to the Hawaiian Islands

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Dispersal to the Hawaiian Islands

• By Stacey Falk

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• Facts
• 2,500 miles of ocean separate North America from
  the Hawaiian Islands.
  
• 3,500 miles of ocean between the small Marianas
  Islands and the Hawaiian chain.
  
• The Hawaiian chain has never been connected to a
  land mass.

www.worldatlas.com
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• How then, did plants and animals cross the large
  oceanic distance to arrive on the Hawaiian
  islands?

• Transportation through the air
• Attached to Birds
• Fruits eaten by Birds
• Drifting in Seawater

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Questions

• What are the two ways in which plants and birds
  are able to travel the long-oceanic distance to
  the Hawaiian islands by drifting through the
  air?
• How can plants and animals be dispersed to the
  Hawaiian islands by attachment to birds?
  
• What accounts for the largest means of seed
  dispersal to the Hawaiian islands than any other
  mechanism?
  
• What adaptations must a plant or seed have for
  dispersal by flotation in seawater?
  
• What advantage does rafting play in dispersal?

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Drifting in the Air

• Organism must be so small, or reproductive
  structure so small, that its dust-like.
  

• Plants that reproduce by means of spores such as
  ferns, mosses, algae, and lichen
  
• Spores so small that a line of a thousand of them
  end-to-end would be an inch long
  
• Nephrolepis exaltata

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Drifting in the Air

• Fern spores more successful at reaching Hawaiian
  island then seeds of flowering plants
  
• 1.4 of the 255 hypothetical original flowering
  plants were dispersed by air flotation
  
• Ohia lehua tree has seeds small enough to suggest
  dispersal through the air
  

www.roddyscheer.com
Metrosideros polymorpha
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Drifting in the Air

• Organism must be able to fly

• Insects.
• Research by entomologist, J. Lindsey Gressitt.
  Sampled air at high attitudes and at sea,
  resulted in a large amount of insects trapped.
  Those caught were the same basic groups of
  insects as those native to Hawaii.
• Passive flight and small body size of insects
  accounts for their dispersal to the island.
  
• Birds.
• Travel through active flight such as migratory
  birds, marine birds, shore birds and waterfowl.
  
• Land birds underrepresented.

Pluvialis dominica fulva
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Drifting in the Air

• Air currents are a crucial factor in the role of
  air as a dispersal mechanism.
  
• Northern Hemisphere jet stream is a
  semi-permanent ultra-high-speed wind which occurs
  at 30-40 thousand feet and could account for such
  dispersal.

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Attached to Birds

• Seeds can become embedded in mud on feet or other
  parts of birds
  
• Estimated 12.8 of the hypothetical original
  flowers arrived this way
  
• Possible if seeds are small, plants grow in wet,
  muddy places, and if migratory birds commonly
  visit
  

Lobelia
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Attached to Birds

• Plant and animals become attached to birds
  feathers by a viscid substance
  
• Accounts for 10.3 of hypothetical original
  flowers
  
• When Plantago seeds become wet they develop a
  slimy covering, which dries and adheres to
  surfaces, such as feathers of a bird

P. Major seeds
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Attached to Birds

• Some Seeds are coated with a sticky substances,
  like rubber cement. This viscid substance makes
  it very easy to become attached to birds feathers.

Pisonia umbellifera
Boerhavia diffusa
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Attached to Birds

• In the dispersal of some fleshy fruits a viscid
  substance is involved.
  
• Clermontia have fruits which break open at
  maturity, revealing tiny seeds which contain a
  white latex. This latex helps to stick the seeds
  to the birds feathers.

Clermontia arborescens
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Attached to Birds

• A mechanical device such as barbs, hooks,
  bristles, prongs, or stiff hairs can attach seeds
  to feathers.
  
• Accounts for estimated 12.8 of native flower
  dispersal.
  
• Bidens, called the beggar tick, have sharp hairs
  and prongs which are barbed and easily attach to
  surfaces.

Bidons pilosa
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Fruits Eaten by Birds

• Fruits eaten by birds was the most effective
  means of seed dispersal to the Hawaiian Islands.
  
• Fruit-eating birds ate the seeds, carried them
  internally, and excreted them on Islands
  
• Accounts for dispersal of an estimated 39 of the
  255 original plants

Vaccinium reticulatum
Cassytha filiformis
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Fruits Eaten by Birds

• Large percentage of fruits and seeds attractive
  to birds in Hawaiian flora.
  
• Fruit color not as important as fruit texture in
  attracting birds.
  
• Abundance of all colors and textures in the
  Hawaiian flora.

Tetraplasandra hawaiiensis Has hairy gray fr
uits
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Fruits Eaten by Birds

• Fleshy fruits are well represented on the
  Hawaiian islands. This is true even among plant
  families which mostly have dry fruits.
  
• Indicates that fleshy fruits is more successful
  for long-distance dispersal
  
• Most members of the mint family have dry fruits.
  The Hawaiian mints, such as Stenogyne, are
  unusual in that they have fleshy fruits.

Stenogyne
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Fruits Eaten by Birds

• Shore bird thought to play major role in
  transporting of fruits and seeds to the Hawaiian
  Islands
  
• Migrate all of the Pacific
• Eat large amounts of fruits and seeds
• Capable of retaining fruits and seeds for days
• Common migratory shore birds include the Pacific
  golden plover and the bristle-thighed curlew

Pluvialis dominica fulca
Numenius tahitensis
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Drifting in Seawater

• 14.3 of native flowering plants adapted to
  oceanic drift.
  
• Adaptations for dispersal in seawater
• Seeds or fruits capable of floating.
• Seeds or plant parts must be able to resist
  seawater for weeks.
  
• Must arrive alive on beach and be able to grow
  there.
  

Pandanus tectorius
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Drifting in Seawater

• The pink-flowered morning glory has seeds cable
  of floating in seawater
  
• Stems and leaves adapted to float in seawater and
  establish when they float on the beach, such as
  the Portulaca

Ipomoea pes-caprae
Portulaca oleracea
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Drifting in Seawater

• Plants which grow well along the beach and have
  seeds resistant to seawater, but have seeds and
  fruits unable to float take advantage of
  rafting
• Rafting is the flotation of an entire plant, or
  entire mats of vegetation
  
• Estimated 8.5 of hypothesized original
  flowering- plants dispersal

Acacia koa
Gossypium sandvicense
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Questions Overview

• What are the two ways in which plants and birds
  are able to travel the long-oceanic distance to
  the Hawaiian islands by drifting through the
  air?
• Organism must be so small, or reproductive
  structure so small, that its dust-like.
  
• Organism must be able to fly

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Questions Overview

• How can plants and animals be dispersed to the
  Hawaiian islands by attachment to birds?
  
• Embedded in mud on feed or other parts of birds
• Attached to feathers by a viscid substance
• Mechanically attached by a device such as barbs,
  hooks, bristles, prongs, or stiff hairs
  

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Questions Overview

• What accounts for the largest means of seed
  dispersal to the Hawaiian islands than any other
  mechanism?
  
• Fruits eaten by birds, then carried internally,
  and excreted on the islands.

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Questions Overview

• What adaptations must a plant or seed have for
  dispersal by flotation in seawater?
  
• Floatability
• Seed or plant part able to resist seawater for
  weeks
  
• Must arrive alive on the beach and be able to
  grow there
  
• What advantage does rafting play in dispersal?
• Seeds and fruits unable to float but are
  resistant to seawater can arrive through
  flotation of an entire plant or mats of vegetation

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References

• Carlquist, Sherwun. Hawaii A natural
  history. The natural history press. Garden
  city, new York. 1970. Pg. 81-111.
  
• Sohmer, S.H. Gustafson R. Plants and flowers of
  Hawaii. University of Hawaii press. Honolulu.
  1987.
  
• Images Hawaii. Hawaii plants and animals.
  http//imageshawaii.com/general_plants.html
  
• Star, Kim. Plants of Hawaii. March 12, 2003.
  http//www.hear.org/starr/hiplants/images/index.h
  tml