Endemism in the Hawaiian Islands

Located about 2300 miles (3680 km) from the nearest continental shore, the Hawaiian Islands are the most isolated group of islands on the planet. The plant and animal life of the Hawaiian archipelago is the result of early, very infrequent colonizations of arriving species and the slow evolution of those species—in isolation from the rest of the world's flora and fauna—over a period of at least 5 million years. As a consequence, Hawai'i is home to a large number of endemic species. The radiation of species described by Charles Darwin in the Galapagos Islands which was critical to the formulation of his theory of evolution is far exceeded in the more isolated Hawaiian Islands.

The relatively short time that the existing main islands of the archipelago have been above the surface of the ocean (less than 10 million years) is only a fraction of time span over which biological colonization and evolution have occurred in the archipelago. High, volcanic islands have existed in the Pacific far longer, extending in a chain to the northwest; these once mountainous islands are now reduced to submerged banks and coral atolls. Midway Atoll, for example, formed as a volcanic island some 28 million years ago. Kure Atoll, a little further to the northwest, is near the Darwin point—defined as waters of a temperature that allows coral reef development to just keep up with isostatic sinking. And extending back in time before Kure, an even older chain of islands spreads northward nearly to the Aleutian Islands; these former islands, all north of the Darwin point, are now completely submerged as the Emperor Seamounts.

The islands are well known for the environmental diversity that occurs on high mountains within a trade winds field. On a single island, the climate can differ around the coast from dry tropical (< 20 in or 500 mm annual rainfall) to wet tropical; and up the slopes from tropical rainforest (> 200 in or 5000 mm per year) through a temperate climate into alpine conditions of cold and dry climate. The rainy climate impacts soil development, which largely determines ground permeability, which affects the distribution of streams, wetlands, and wet places.

The distance and remoteness of the Hawaiian archipelago is a biological filter. Seeds or spores attached to a lost migrating bird's feather or an insect falling out of the high winds found a place to survive in the islands and whatever else was needed to reproduce. The narrowing of the gene pool meant that at the very beginning, the population of a colonizing species was a bit different from that of the remove, contributing population.

Island formation

Throughout time, the Hawaiian Islands formed linearly from northwest to the southeast. A study was conducted to determine the approximate ages of the Hawaiian Islands using K–Ar dating of the oldest found igneous rocks from each island. Kauai was determined to be about 5.1 million years old, Oahu about 3.7 million years old and the youngest island of Hawaii about 0.43 million years old.[1] By determining the maximum age of the islands, inferences could be made about the maximum possible age of organisms inhabiting the island. The newly formed islands were able to accommodate growing populations, while the new environments were causing high rates of new adaptations.

Human arrival

Human contact, first by Polynesians and later by Europeans, has had a significant impact. Both the Polynesians and Europeans cleared native forests and introduced non-indigenous species for agriculture (or by accident), driving many endemic species to extinction. Fossil finds in caves, lava tubes, and sand dunes have revealed an avifauna that once had a native eagle,[2] two raven-size crows, several bird-eating owls, and giant ducks known as moa-nalos. Around 861 species of plants have been introduced to the islands by humans since its discovery by Polynesian settlers, including crops such as taro and breadfruit.[3]

Today, many of the remaining endemic species of plants and animals in the Hawaiian Islands are considered endangered, and some critically so. Plant species are particularly at risk: out of a total of 2,690 plant species, 946 are non-indigenous with 800 of the native species listed as endangered.[4]

Terrestrial animals

Mammals

Birds

Freshwater fishes
None of Hawaii's native fish are entirely restricted to freshwater (all are either anadromous, or also found in brackish and marine water in their adult stage).

Terrestrial invertebrates
This list is incomplete; you can help by adding missing items with reliable sources.

Insects

Crustaceans
  • Atyoida bisulcata (a freshwater shrimp)
  • Halocaridina (a genus of marine and brackish water shrimp)
  • Hawaiian river shrimp (Macrobrachium grandimanus)

Spiders

Gastropods

Gastropods are snails.[6]

  • Oahu tree snails (Achatinella) - threatened, several already extinct
  • Auriculella (a genus of land snails) - threatened, several already extinct
  • Erinna (a genus of freshwater snails) - one vulnerable species, the other possibly extinct
  • Gulickia alexandri (a land snail) - critically endangered
  • Newcombia (a genus of land snails) - threatened, one already extinct
  • Neritina granosa (a freshwater snail) - vulnerable
  • Perdicella (a genus of land snails) - threatened, several already extinct

Marine animals

Marine fishes
Main article: List of fish of Hawaii

Cnidarians
  • Finger coral (Porites compressa)
  • Thick finger coral (Porites duerdeni)
  • Brigham's coral (Porites brighami)
  • Molokaʻi cauliflower coral (Pocillopora molokensis)
  • Irregular rice coral (Montipora dilatata)
  • Blue rice coral (Montipora flabellata)
  • Sandpaper rice coral (Montipora patula)
  • Verril's lump coral (Psammocora verrilli)
  • Serpentine cup coral (Eguchipsammia serpentina)
  • Grand black coral (Antipathes grandis)
  • Bicolor gorgonian (Acabaria bicolor)
  • Small knob leather coral (Sinularia molokaiensis)

Plants
This list is incomplete; you can help by adding missing items with reliable sources.

Apiales

Arecales
  • Loulu – (Pritchardia fan palms)

Campanulaceae

Asteraceae

Cornales

Fabales

Gentianales
  • Na'u (Gardenia brighamii) - critically endangered
  • Pua ʻala (Brighamia rockii) - critically endangered

Malvales

Myrtales

Rosales

See also

References
  1. Fleischer, RC; McIntosh, CE; Tarr, CL (1998). "Evolution on a volcanic conveyor belt: using phylogeographic reconstructions and K–Ar-based ages of the Hawaiian islands to estimate molecular evolutionary rates". Molecular Ecology. 7 (4): 533–45. doi:10.1046/j.1365-294x.1998.00364.x. PMID 9628004. S2CID 4602499.
  2. Fleischer, Robert; Olsen, Storrs; James, Helen; Cooper, Alan (October 2000). "Identification of the Extinct Hawaiian Eagle (Haliaeetus) by mtDNA Sequence Analysis" (PDF). The Auk. 117 (4): 1051–1056. doi:10.1093/auk/117.4.1051. Retrieved May 23, 2018.
  3. Harris, David (2005). Prance, Ghillean; Nesbitt, Mark (eds.). The Cultural History of Plants. Routledge. p. 27-28. ISBN 0415927463.
  4. David Pimentel; Lori Lach; Rodolfo Zuniga & Doug Morrison (January 24, 1999), "Environmental and Economic Costs Associated with Non-Indigenous Species in the United States", Cornell Chronicle, Cornell University, retrieved April 3, 2015
  5. Lindstrom, D.P., M.J. Blum, R.P. Walter, R.B. Gagne and J.F. Gilliam, 2012. Molecular and morphological evidence of distinct evolutionary lineages of Awaous guamensis in Hawai’i and Guam. Copeia (2):293-300.
  6. Fenner, Douglas (2005). Corals of Hawai'i : field guide to the hard, black, and soft corals of Hawai'i and the northwest Hawaiian Islands, including Midway (1 ed.). Honolulu, Hawai'i: Mutual Pub. ISBN 1-56647-673-9.

Further reading
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