ECOVIEWS: Silverwords and other unusual species inhabit Hawaii

  • Posted: Sunday, February 17, 2013 1:25 a.m.

The Haleakala silversword plant grows only on the top of Haleakala volcano in Maui. Of the diverse array of plants I saw in the Hawaiian Islands, silverswords were one of the few native plants living in their natural habitat. Most species of plants and animals in our southernmost state found a home there only in the last couple of centuries, and they were introduced to the islands by people – sometimes intentionally, sometimes unwittingly. Any species found in Hawaii was once an immigrant or is the descendant of one.

Oceanic landforms that rose from the sea as volcanoes, the Hawaiian Islands represent an environmental marvel. Any animal or plant in Hawaii had to have an ancestor that came from somewhere else, but species that arrived from a million years up to a few centuries ago can now be considered native Hawaiian species. The evolutionary process began soon after each species arrived. At least it did for those that survived long enough to begin to change. To survive, a species had to adapt to its new environment, which was undoubtedly different from its mainland origin. The slow but inexorable evolutionary process took many thousands of years for some species; for others, the changes occurred over hundreds of thousands of years.

The silverswords I saw in Haleakala National Park were at an elevation almost two miles above sea level. Most plants that might compete with them and the animals that might eat them would find the environment inhospitable at best. The first silversword plant I saw in the wild brought to mind the image of a basketball-size hedgehog with long, silver-coated spines. In the same family as dandelions, silverswords are a fine example of evolution. Imagine a dandelion or aster adjusting to a terrain of ancient lava substrate that supports sparse vegetation.

Add cold temperatures, arid conditions, constant wind and intense sunlight year round, and you have the environment to which the silversword adapted. The closest surviving relative of the Haleakala silversword is the endangered Mauna Loa silversword, which is found in similar habitat on the neighboring island of the Big Island (i.e., Hawaii). Cattle, pigs and goats are among the threats that led to near extinction of silverswords. The National Park Service no longer lets them eat the rare plants.

Polynesians arrived on the islands about 1,500 years ago. The Hawaiian Islands have been shaped by human hands for so long that the mix of endemics and invaders, both plant and animal, is remarkable. One day, over the span of just a few minutes, I saw free-living plants and animals from Indonesia, Madagascar and six continents. I also saw a couple of species that are considered native to Hawaii. For an ecologist, exploring the natural history of the Hawaiian Islands might be compared to window-shopping at a store in which merchandise from Walmart, Tiffany’s, Home Depot and Toys-R-Us is displayed randomly throughout the store. When you turn a corner, you have no idea what to expect in the next aisle.

Some introduced species, such as the predatory Indian mongoose, have had significant impact on the native fauna. The mongoose was introduced to the islands in the 1880s to protect the sugarcane industry from rats that were eating into the plantation owners’ profits. As with many such introductions, things didn’t go according to plan. The mongoose found it was much easier to eat native birds and their eggs than to chase rats. These ferret-like carnivores still slink around on at least three of the larger islands.

Endangered green sea turtles and monk seals frequent Hawaiian beaches. Rare Hawaiian geese walk around the tops of volcanoes where silverswords live. These species were not introduced by humans and can qualify as extant Hawaiian natives. Of Hawaii’s remaining flora and fauna, probably more than 95 percent are newcomers that have joined this unusual ecosystem in the last couple of centuries. Collectively, native and immigrant species make Hawaii a place of wonder for any botanist, zoologist or ecologist – and a beautiful vacation spot for anyone.

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Whit Gibbons is an ecologist and environmental educator with the University of Georgia’s Savannah River Ecology Laboratory.

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