Dispersal to the Hawaiian Islands

By: Stacey Falk

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

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

Questions:1. 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?

2. How can plants and animals be dispersed to the Hawaiian islands by attachment to birds?

3. What accounts for the largest means of seed dispersal to the Hawaiian islands than any other mechanism?

4. What adaptations must a plant or seed have for dispersal by flotation in seawater?

5. 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

1) Organism must be so small, or reproductive structure so small, that it’s dust-like.

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

Metrosideros polymorpha

www.roddyscheer.com

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.

2. Organism must be able to fly

Pluvialis dominica fulva

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

Lobelia

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

Attached to Birds

Boerhavia diffusa Pisonia umbellifera

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

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

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

Fruits Eaten by Birds

Vaccinium reticulatum

Cassytha filiformis

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.

Tetraplasandra hawaiiensis

Has hairy gray fruits

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

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

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

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

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

Questions Overview

1. 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:

2. 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:

3. 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:4. 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

5. 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

References:

1) Carlquist, Sherwun. “Hawaii: A natural history”. The natural history press. Garden city, new York.

1970. Pg. 81-111.

2) Sohmer, S.H.; Gustafson R. Plants and flowers of Hawai’i. University of Hawaii press. Honolulu. 1987.

3) Images Hawaii. Hawaii: plants and animals. http://imageshawaii.com/general_plants.html

4) Star, Kim. Plants of Hawaii. March 12, 2003. http://www.hear.org/starr/hiplants/images/index.html