Hawaiʻi’s remoteness can explain much of the uniqueness of its flora and fauna. The islands were, and continue to be, formed on a tectonic plate slowly moving over a hotspot of volcanic activity with each island formed in chronological sequence, thus of different age. The island chain is a very long way from and has never been connected to any other large landmass. Organisms that got to the islands by wind, water, or wings found a diverse set of habitats in close proximity and ranging from rain forest to alpine. New arrivals often had little competition which resulted in different evolutionary drivers than in areas with many other species already present.
The basic concepts are described by K. Kaneshiro in the book Conservation Biology in Hawaiʻi: http://manoa.hawaii.edu/hpicesu/book/1988_chap/ in chapter 10 entitled ‘Uniqueness of Hawaiʻi’s Biota’ which also has some specific information on the Drosophila picture-wing flies, one of the most unique adaptive radiations anywhere.
A site especially good for description of dispersal of plants to and within islands, including examples from Hawaiʻi, by a pioneer Hawaiʻi researcher is here: http://www.sherwincarlquist.com/.
An excellent introduction to the general concepts of evolution in Hawaiʻi is the primer Evolution in Hawaiʻi, A Supplement to Teaching About Evolution and the Nature of Science developed by the National Academy of Sciences and is available here: http://nap.edu/10865 and the clickable table of contents is here: https://www.nap.edu/read/10865/chapter/1#v. A downloadable pdf of the book is also available at the first link.
The geography of Hawaiʻi helps make its uniqueness. This includes:
- Geology and Soils
- Volcanism, craters, limestone
A good overall source of information and explanation is the Chapter 2 (Physical Environment) of the Atlas of Hawaiʻi: http://www.ulukau.org/elib/cgi-bin/library?c=atlas&l=en.
The climate varies greatly over short distances and in particular precipitation. This can be readily seen looking at rainfall maps here: http://rainfall.geography.hawaii.edu/. Price et al. (2012) developed seven moisture zones by calculating a moisture availability index that considers mean annual precipitation, potential evapotranspiration, and elevation (https://pubs.usgs.gov/of/2012/1192/). This resulted in three primary moisture zones (Dry, Mesic, and Wet) across the state, which was further subdivided into seven moisture subzones (three Dry subzones, two Mesic subzones, and two Wet subzones).
Temperature inversions also plays a role in controlling climate as explained here in a paper by Giambelluca and Nullet (1991): https://pdfs.semanticscholar.org/a23c/7ef9ea03de3e1f6eee83fdce247a3b708a0a.pdf. “An inversion is a layer in the atmosphere in which temperature increases (not decreases) with height. In Hawai’i, this commonly occurs at about 1800 to 2400 meters (6000 to 8000 feet)… The presence of the trade wind inversion influences many aspects of Hawaiian climate, including: 1) limiting cloud height and causing flat cloud decks to form, 2) limiting the amount of rainfall the islands receive, 3) reducing relative humidity …, and 4) producing dry air and clear skies at the highest elevations.” Inversions are important in controlling rain because they control how high air can rise and therefore can cause lighter rain showers or clouds with no showers at all.
The age of the Hawaiian islands ranges from 0.375 million years (My) for Mauna Kea on Hawaiʻi Island to 27.7 My for Midway Island with the oldest main island of Kauai at 5.1 My, according to U.S. Geological Survey Professional Paper 1350. This chronological sequence allowed for new colonizations to islands of many different ages – “island-hopping”. In addition, the islands have great geological complexity. Detailed maps of island geology are here: https://pubs.usgs.gov/of/2007/1089/
Topographic variation can be seen in the USGS topographic map of Hawaiʻi which is available via the USGS topo viewer here: https://ngmdb.usgs.gov/topoview/viewer/#4/40.01/-100.06.