Part 1: Evolutionary Processes in the Hawaiian Islands

Part 1: Evolutionary Processes in the Hawaiian Islands

Key to Species Classifications:

Native—Arrived in the Hawaiian Islands without the aid of humans (indigenous), or evolved in the Hawaiian Islands (endemic).

Indigenous—Native to the Hawaiian Islands and other places.

Endemic—Evolved in the Hawaiian Islands from an indigenous species; native to the Hawaiian Islands and nowhere else.

Polynesian Introduction—Brought to the Hawaiian Islands by the early Polynesian settlers.

Post-Contact Introduction—Brought to the Hawaiian Islands after Western contact (1778).

Naturalized—Not native to the Hawaiian Islands, but now growing wild in the Hawaiian Islands.

After the volcanoes of the Hawaiian Islands formed and cooled, the weathering of the sun, rain, and wind began to break down the lava rock into soil. Primitive plants known as lichens also helped to create soil, allowing more plant species to take hold.

These plant species in turn created new habitats that allowed the Hawaiian Islands’ original colonizing species to evolve, over millions of years, into thousands of plant, insect, and bird species.

Relatively few species were able to reach the Hawaiian archipelago before humans arrived, but those species that did become established were able to take advantage of the Hawaiian Islands’ diversity of habitats and ecosystems.

The original colonizing species evolved into an array of uniquely adapted species that gradually transformed the Hawaiian Islands barren and rocky volcanoes into lush tropical islands full of life.

Colonization—Native and Endemic Species

Located more than 2,400 miles (3,862 km) from the nearest continental land mass, the Hawaiian Islands were not easily colonized by new species prior to the arrival of humans. The extreme geographical isolation of the Hawaiian Islands also limited the types and the numbers of species that became established.

All of the Hawaiian Islands’ native species are divided into two categories: indigenous and endemic. Species that somehow made it to the Hawaiian Islands without the aid of humans, and then were able to establish native populations, are now classified as indigenous to the Hawaiian Islands. These indigenous species are native to the Hawaiian Islands, and are also native to other places (wherever the species originally came from).

The other category of native species is the endemic Hawaiian species, which evolved in the Hawaiian Islands from species that were already established in (and thus native to) the Hawaiian Islands.

Endemic Hawaiian species may have evolved from an indigenous Hawaiian species or from another endemic Hawaiian species. In either case, all endemic Hawaiian species evolved in the Hawaiian Islands, and thus are unique to the Hawaiian Islands (found naturally nowhere else).

Hawai‘i’s geographic isolation and diversity of habitats and food sources led to the evolution of many new (endemic) species from the relatively few colonizing species that were able to make it to the Hawaiian Islands and reproduce.

This evolution of new species from relatively few colonizers resulted in extremely high rates of endemism for various categories of species. For example, about 79% of the native flowering plant species of the Hawaiian Islands are endemic, along with about 70% of native ferns of the Hawaiian Islands. About 25% of native Hawaiian reef fish are endemic to the Hawaiian Islands.

Methods of Arrival—

How Native Species Traveled to the Hawaiian Islands

Indigenous species inhabiting the Hawaiian Islands arrived in the Islands by a variety of methods. For example, seeds floated to the Hawaiian Islands on the ocean, or were carried in the wing feathers or in the digestive tracts of birds, or in mud on the birds’ feet.

The colonizing bird species may have come to the Hawaiian Islands on their natural migration tracks, or arrived after being blown off course by a storm.

Snails and other species may have been transported to the Hawaiian Islands by hitching a ride on floating logs or on rafts of debris that floated over the Pacific Ocean and washed up on Hawaiian shores. Tiny snail eggs were also carried to the Hawaiian Islands embedded in mud in the feet of birds.

Insects and spiders in far distant places were lifted by winds high into the jetstream, more than 8 miles (13 km) up, where they were carried out over the Pacific Ocean at more than 120 miles per hour (193 km/hr) and then set down on the Hawaiian Islands, there to remain and multiply.

For many species, the journey to the Hawaiian Islands was too long and the odds too great. Even over many millions of years the species were never able to reach the Hawaiian Islands, or if they did, there was not suitable habitat for them to survive. Some species may have arrived in the Hawaiian Islands in such small numbers that they were not able to establish breeding (reproducing) populations.

It is estimated that about 39% of plant species in the Hawaiian Islands came in the stomachs of birds; about 13% arrived in mud on birds’ feet; about 23% arrived after being stuck to the feathers of birds; about 9% arrived on rafts of seaweed or debris on the ocean; and about 1.4% came by floating through the air to the Hawaiian Islands.[i]

Many plants and animals that are very common in other places never became established in the Hawaiian Islands until humans brought the species to the Hawaiian Islands.

For example, in the Hawaiian Islands there are no gymnosperms (e.g., pine trees), no native amphibians, no native terrestrial reptiles, and no native ants. However, all of these organisms are now found in the Hawaiian Islands, having been introduced to the Islands by humans.

Endemism and Adaptive Radiation

Species that somehow were able to traverse the vast distance over the Pacific Ocean to the Hawaiian Islands and become established in the Hawaiian Islands (without the aid of humans) were then able to adapt to a wide variety of environmental conditions (ecological niches) found in the Hawaiian Islands.

Populations of species often became divided, with each separated sub-population adapting to different habitats and food sources, and eventually evolving into completely new species.

For example, one finch species that established itself in the Hawaiian Islands millions of years ago evolved into at least 50 species and subspecies of Hawaiian honeycreepers.

The evolutionary process whereby one species evolves into many new species is known as adaptive radiation. The Hawaiian Islands are renowned for their historical record of adaptive radiation, particularly regarding bird and insect species.

Over hundreds of generations, many plant, animal, and insect species evolved adaptations to the unique conditions found on each of the Hawaiian Islands.

Many of these adaptations distinguished the separate populations, which eventually evolved into unique species or subspecies, endemic to each particular island. For example, the fragrant mokihana plant (Pelea anisata) is endemic to the uplands of Kaua‘i, as is the puaiohi (Myadestes palmeri), a tiny pink-legged forest bird.

Some native Hawaiian species may be endemic to very small areas. For example, the endangered plant known as koki‘o ke‘oke‘o (Hibiscus waimeae subspecies hannerae, white hibiscus) is found only in a few northwest Kaua‘i valleys, including the valleys of Limahuli and Hanakāpī‘ai.

Native Hawaiian species isolated within a particular valley for many thousands of years often developed variations that aided their survival in the particular habitat. This isolation often led to distinct subpopulations of species that eventually became distinguishable as endemic subspecies or completely new species.

An ancient proverb states, “‘O‘opu peke o Hanakāpī‘ai.” (“The stunted ‘o‘opu fish of Hanakāpī‘ai,” referring to “...the ‘o‘opu of Hanakāpī‘ai, which are said to be plump and shorter in length than those elsewhere. Sometimes applied humorously to a short, plump person.”[ii]

The evolutionary process of adaptive radiation allowed the relatively few colonizers of the Hawaiian Islands to develop into a vast array of life forms that today constitutes the diverse native flora and fauna of the Hawaiian Islands.

(For a more in-depth explanation of adaptive radiation, see this book’s Introduction as well as the Honeycreepers and Honeyeaters section in Native Birds of the Hawaiian Islands, Chapter 7.)

[i]Juvik, James O. Biogeography in Atlas of Hawai‘i: Third Edition. Edited by Sonia P. Juvik and James O. Juvik. Honolulu: University of Hawai‘i Press, 1998.

[ii] p. 276, Pukui, Mary Kawena. ‘Ōlelo No‘eau: Hawaiian Proverbs & Poetical Sayings. Honolulu: Bishop Museum Press, 1983. Proverb 2529.