Wilderness Underfoot: The natural scale of things, Part 1

StoryImage( ‘/Images/Story//Auto-img-115514310916604.jpg’, ”, ‘Humans are giants in comparison to most other creatures – This boy is 16,000 times the weight of the luna moth in his hand.’);

Just try to imagine this: the earth’s largest living organism is more than 1,000,000,000,000,000,000,000 times larger than the smallest.

The size of a living thing affects every other aspect of its existence, such as where it will live, how it will feed, its growth rate, its reproductive rate, even the length of its life.

In general, smaller organisms reach maturity faster. They reproduce earlier and in greater numbers. And they’re capable of quickly adapting to occupy a greater range of ecological niches. Larger organisms, on the other hand, tend to have slower metabolisms, and they take longer to reach maturity. But they usually live longer than smaller organisms.

Given the enormous sizes of such modern organisms as the African elephant, the blue whale or the giant Sequoia tree, you might wonder how humans fit into the scale of things.

Surprisingly, with an average adult weight of 120 to 180 pounds, humans are giants compared to most other organisms. For one thing, we’re thousands of times larger than the most plentiful group of living things on earth, the insects. We’re so large that entire ecosystems of microbes can live in and on our bodies.

If you compare sizes of native animals living here in Illinois, humans and white-tailed deer are tied as the biggest of them all. (This excludes bison, which became extinct here and were then reintroduced.) We’re big, but next to our state’s largest organisms, the trees, we and all the other animals are comparatively quite small.

The meaning of “largest living organism” is up for debate. For example, a giant fungus, Armillaria ostoyae, in the Blue Mountains of Oregon covers 2,200 acres. Most scientists say it doesn’t really represent a single organism, but rather, an interdependent colony of fungi that form a superorganism.

A coral reef could also be considered a superorganism. The world’s largest reef, Australia’s Great Barrier Reef, stretches more than 1,200 miles. The argument about whether a collection of organisms can be considered a single living entity gets somewhat messy when it comes to the entire mass of life on the planet, which in its own right may qualify as one whopper of a superorganism!

Setting aside the superorganism debate, the largest animal ever known to have lived on our planet is the blue whale. This magnificent modern animal measures up to 100 feet in length and weighs a chunky 200 tons. That’s about the same volume as a crowd of about 2,500 adult humans.

At the other end of the scale is the smallest known organism, a tiny microbe with a big name—Nanoarchaeum equitans. This microbe lives on a thermal vent in cold ocean waters off Iceland. At 400 nanometers each, 50,000 of them could stretch across the period at the end of this sentence.

From the Aug. 9-15, 2006, issue

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