Hawaii Ecology

Destroying volcanoes:

Hawaii volcanoes are huge piles of mechanically weak rock. As eruptions build up a volcanic edifice, the force of gravity works to destroy it in two distinct ways:


Hawaii rift zones from USGS
Rift zones: As the volcano grows, its material spreads outward, resulting in rifts - zones of weakness that provide magma with easier access to the surface. These, in turn, become foci of new eruptions (E.G. Kilauea's eastern rift zone in recent times.)


Holei Pali from Chain of Craters Road
Slumps: Places where unconsolidated ground detaches from its substrate and moves downhill as a more or less coherent block. Often seen on a small scale but occasionally on a gigantic one. As an active volcano like Mauna Loa or Kilauea grows, the angle of its slope steepens until its material can't withstand the force of gravity. As a result, giant blocks of rock detach and slide down-slope as huge slump blocks. These are revealed by giant head scarps at their uphill margins. Holei Pali (right) and Hilina Pali on the slopes of Kilauea are examples. On a grander scale, underwater slumping has moved thousands of km3 of material on the adjacent sea floor.

Weathering and Erosion: As soon as volcanic rock forms, agents of weathering attack it. These can include the mechanical forces (name examples) and chemical ones. Indeed, igneous rock tends to be vulnerable to the slight acidity of rainwater. (Why is rainwater acidic?)


Basalt polygons etched by rainwater at Whittington Beach, HI
Physical parameters of weathering:


Hawaii topography

These weathering products are transported downhill by the various agents of transport. In Hawaii, gravity and running water are particularly important. The result is that older volcanoes are incised by steep valleys. A survey of the island's topography shows that these canyons are not distributed randomly.

What two factors might influence their distribution?


Canyons of Hamakua District from Shutterstock

Because chemical weathering by low pH rainwater is such an important factor, weathering tends to be concentrated in places receiving the most rainfall - High elevations on the windward side of the island, resulting in the erosion of amphitheaters that drain to the ocean through narrow canyons. In places with shallower slopes and less rainfall, soils can form.


Waipio Valley from Wall Street Journal

Paradox: It all seems very simple until you start thinking about global climate change. In Hawaii's most eroded regions, we see broad, flat-bottomed valleys like Waipio (right) and Pololu, whose floors are filled with sediment that forms the best agricultural soils on the island. How did they form?

Picture the scene 20,000 years ago at the last glacial maximum, when sea-level was up to 80 m lower than today. The canyons actually cut much deeper, but filled with sediment as sea level rose to modern levels.

In all of this, we see that Hawaii geography is connected to global systems that govern their overall conduciveness to habitation by organisms.


Kipuka from Wikipedia

Island Biogeography

Island Biogeography is the study of the parameters effecting the species diversity of insular habitats. These may be:

It's basic principles were presented in the 1960s by Robert MacArthur and E. O. Wilson. In a nutshell, the diversity of species on an island is determined by:

At the crudest level, these factors are determined by:



Native land vertebrates of Hawaii
These principles have been empirically verified through studies in places like the Caribbean, where reptiles, mammals, and even amphibians can raft from island to island. Hawaii is an extreme case, being the world's most remote major land mass, and being roughly equidistant from the New and Old World. Moreover, there has been no time in Earth history when it wasn't remote. Applying the principles of island biogeography, we are not surpised to find:


Ohia lehua (Metrosideros polymorpha)
In contrast, there are plenty of plant species and of native (naturally occurring but not limited to) and endemic (occurring nowhere else) Hawaiian birds. Most arrived by air.

Plants: 255 original endemic species tend to:



Hawaiian fruit flies in combat from School of Ocean and Earth Science Technologies
Animals: Hawaiian endemic fauna is limited to:

Expanding to native fauna, we gain some migratory sea birds and shore birds.

And yet the Hawaiian Islands have many introduced invasive species:

These lists reveal a remarkable pattern of extinctions and recent introductions. How did this happen?



Hawaiian honeycreepers from Douglas Pratt

Pristine Hawaii

The roster of endemic plants and animals of Hawaii reflects the demands of dispersal over thousands of miles of ocean - effectively impossible for any non-flying animal. No surprise that ancient Hawaii's faunas were dominated by birds. Hawaii hosts endemic adaptive radiations of:



Hawaiian Honeyeaters from Fleischer et al., 2008
These living radiations were accompanied by extinct ones, including:



The Hawaiian goose (Nene)
Today, only their flying relatives remain: All closely related to relatives in North America and Eurasia.

Alongside them live land birds with close relatives in other places:



The Hawaiian scene just prior to discovery at the National Zoo from Studia Mirabilium

Evolutionary Pattern I - Flightlessness

Hawaii is not the only island where immigrating birds have lost the power of flight. Consider: among many others.

Flight is useful for:

but it is very metabolically expensive. Thus, birds that find themselves in pleasant environments without land predators tend quickly to lose the ability.

Moreover: When your home is a small island in the middle of the ocean, the ability to fly becomes a hazard because it allows you to be blown out to sea.


Blue-faced honeyeater (a true meliphagid)

Hawaii O'o (a Hawaiian honeyeater)

Evolutionary Pattern II - Convergent Evolution

From their discovery until Fleischer et al., 2008, ornithologists considered the honeyeaters of Hawaii to be members of Meliphagidae - the Australasian honeyeaters, based on morphology and behavior. Imagine our surprise when molecular phylogenetic analyses showed that they had been close relatives of New World silky flycatchers and waxwings.

The Hawaiian honeycreepers, similarly, resemble the true honeycreepers of the New World, but are instead closely related to seed-cracking finches.


The discovery of Hawaii from John Harrington

What Happened?

Prehistoric Hawaii suffered two ecological blows, each a one-two punch:

The Polynesian Discovery of Hawaii - 300 - 600 CE

Prior to the modern age, the Polynesians were the most widespread nationality on Earth. Polynesian success stemmed from the combination of: The consequences: But there were unintended introductions: to destroy the primary producers on which native animals fed. Adding insult to injury, over-harvesting of creatures like the "honeyeaters" for feathers hastened their decline. By the time of Hawaii's discovery by Europeans, moa nalos were a distant legend, and "honeyeaters" were in sharp decline.



Gold dust day gecko in Kona District - descended form escaped pet

The World's Discovery of Hawaii - 1778 to present

British Capt. James Cook made the first documented (!) outside contact with Hawaii. This roughly coincided with the establishment of a unified Hawaiian government, which allowed widespread foreign settlement. This drastically accelerated the trends set in motion by the Polynesians, with the conversion of land to farming and ranching, and the wholesale importation of invasive species, by design or accident.

In the last century, insult has been added to injury through the widespread importation of invasive birds, mammals, reptiles, and amphibians. Many of these are ecological generalists or disturbed habitat specialists who are right at home in Hawaii's. Sometimes they arrive by accident (stowaways in shipments) and sometimes by human folly (deliberate well-intentioned introductions and released pets). Some bad actors:

In short, the Hawaiian archipelago is a kind of anti-Galapagos. The setting of one of the world's most disturbed and transformed habitats, with no equilibrium in sight.