Dispersal to the Hawaiian Islands By: Stacey Falk



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Dispersal to the Hawaiian Islands

  • By: Stacey Falk


Facts:

  • 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.



How then, did plants and animals cross the large oceanic distance to arrive on the Hawaiian islands?

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



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?



Drifting in the Air

    • 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


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



Drifting in the Air

  • 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.


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.


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



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



Attached to Birds



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.



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.



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



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.



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.



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



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.


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



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



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 it’s dust-like.
    • Organism must be able to fly


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


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.


Questions Overview:



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 Hawai’i. 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.html



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