Not the most euphonious title. But paleobiogeography is a marvelous thing to me. To put it in a slightly more simple way, it’s about how populations have expanded and contracted in an area over time.
Take my hometown of Chicago for example. Now back when most things I knew about animals came from ZooBooks, (Yes, that will date me!) I thought the Chi was known for the snow, deep dish, and Ditka. But 10,000 years ago, my beloved city, like the rest of America would have been known for its awesome faunal assemblage. Like Camelids. Camel populations today are mostly centered around Asia (Bactrian & Dromedary) and South America (Llamas). Imagine my preteen surprise when I found out that not only were camels part of Midwest’s fauna but much of the group’s evolutionary history can be found right here in the U.S. There are camel fossil here dating back to the late Eocene. In fact, the only time in the last 40 million years there have not been any camels native to the U.S. is right now, the last 10,000 years. That’s like saying camels have been here all week, except for the last 2 and a half minutes. We just missed them. There could have been a real possibility of seeing this sign on the Eisenhower expressway:
Imagine the car insurance rates.
So that’s a short background on my interest in population ranges over time, what does this have to do with the weird, Captain Cook way of spelling Hawaii? Well to me its easy to see how the biota have changed over time here in Hawaii. Not only are the islands some of the most isolated in the world, thousands of miles from the nearest continents, but the Hawaiian chain is also special because it is being replenished by the Hawaiian hotspot. When you look at the pacific sea floor you can see this. The chain of volcanoes created by the hotspot stretching all the way back to the Aleutian Trench.
This isolation allows for amazing evolutionary experiments. If, by chance, some plant or animal manages to cross the thousands of miles to reach the archipelago, they have a chance to radiate into niches not normally available. Each volcano arises from the sea empty, devoid of life. Those pioneering individuals get a black slate to evolve in. Anything from dabbling ducks that evolved into flightless geese-like creatures (Moa-Nalos), to giant lobelias, to carnivorous caterpillars; plants and animals in Hawaii have been able to radiate spectacularly.
However it is still difficult to maintain a distinct Hawaiian fauna over a long period of time because of the temporary nature of each individual island. To stand for long periods of time, the floral and faunal elements from older islands must be able to disperse to newer islands. Imagine those big paddle boats plying the Mississippi. If you were a rat, you’d have to hop from one spoke to another as an individual spoke submerged. It takes effort and luck for plants and animals to disperse from one island to another but it much easier to travel 50 miles from one island to another than 5,050 from a continent to the islands.
So the hotspot has been active for at least 70 million years. You can see that from the sea floor maps. Yet many of the native biota have been estimated to only arrived when Kauai formed, roughly 4-5 million years ago. What is going on here?
It turns out that the strength of the eruptions from the hotspot have not always been consistent. In the past 30 million years, there have been only 2 periods where the hotspot has been active enough to produce high islands above 3,000 ft. Why is 3,000 ft important? The latitude where the Hawaiian Islands sits is very dry. We don’t get the great cold fronts/warm fronts sweeping through like the mid-latitudes. No rain, no rainbows, as the saying here goes. And no diverse ecosystems. The main reason certain areas of Hawaii receive so much rain is due to the persistent trade winds and orographic lifting. And that takes mountains high enough to force condensation. So it all boils down to this, was the hotspot active enough to make a volcano that not only breaks the 30,000 ft to the surface of the ocean, but the additional 3,000 some odd feet to create the moisture uplifting and condensation needed for a wide variety of ecosystems before the motion of the Pacific Plate moved it away?
Here is where I get excited. The first highly active phase was around 18-13 million years ago. The high islands at this time were Laysan, Gardner, and LaPerouse (the current French Frigate Shoals). Gardner is particular was huge, roughly equivalent in size to the current Big Island. The flora and fauna that found its way there must have been amazing. Unfortunately, after that, the hotspot went through a lull. Not as many volcanoes broke the surface and even those that did were not as large. Following this lull was the second peak period. This period formed/are forming the current main Hawaiian Islands. By the time Kaua’i arose, the former high islands at Gardner and Laysan had eroded considerably and were also fairly distant from the newly emerging island. If we go back to the paddle steamer analogy, it’s like suddenly having huge gaps between the spokes. Our poor rat would have difficulty keeping his head above water. Needless to say, many elements of this “ole Owyhee” did not transfer down to this second peak period.
But some did. When people talk about the 3 W’s of wing, wind and water for how plants and animals arrive in the current Hawaiian islands, they are usually talking about different areas on the globe. It could be Asia, North America, Polynesia. But luckily we can talk about a few elements that didn’t travel thousands of miles to get to the islands; they were already here. Elements that come from a place that doesn’t exist anymore. Elements with a memory of times long past, when Gardner was king. The most prominent of these were the O’o Birds of the family Mohoidae (Pictured at the beginning of the post) and the Hawaiian Lobeliads. These are what I will talk about in part II.
Price, J. P. & Clague D.A. 2002 How old is the Hawaiian Biota? Geology and Phylogeny suggest a recent divergence. Royal Publishing Society
USGS http://pubs.usgs.gov/gip/dynamic/Hawaiian.html “The long trail of the Hawaiian Hotspot”