The Diversity of Life
By Bruce A. Stein
United States encompasses an enormous piece of geography stretching from above the Arctic Circle in the north to below the Tropic of Cancer in the south. Ensconced between these two extremes is a tapestry of habitats that support a remarkable array of plant and animal species. The United States is one of the most diverse temperate-zone nations on Earth. Among the nation’s flora and fauna are a number of truly superlative species. Among trees, for instance, the U.S. harbors both the world’s tallest (coast redwood) and oldest (bristlecone pine). In all, more than 200,000 species of plants, animals, and microbes have been described and named scientifically, with many more yet to discover. Although there is no single source that catalogues all of these species, the NatureServe Explorer website is an excellent place to learn about many of the best known and most beloved of these plants and animals.
Most people are familiar with those wildlife species that are common in and around their homes, whether that be mammals such as raccoons, white tailed deer, or coyotes; birds such as northern orioles, American goldfinches, or red-tailed hawks; or fishes like brook trout, northern pike, or large-mouth bass. These wildlife neighbors help enrich our lives and anchor us to our homes through defining a sense of place. It is no coincidence that each state in the union has formally adopted such natural symbols as state birds, wildflowers, and trees. Our biological riches, however, go well beyond such well-known creatures, and from a conservation perspective many of the species of greatest interest—and concern—are those that are not so readily apparent to casual observers, or are extremely localized.
Salamanders, for example, are often evident only to those setting out to actively look for them, but play a huge ecological role. In many southeastern forests salamanders may account for more biomass -- “meat” if you will -- then all the large mammals such as deer found in those same forests. Ranging in size from tiny, soil dwelling creatures to aquatic behemoths nearly a yard long, there are more different types of salamanders in the United States than in any other country on Earth.
Plants are the ultimate renewable energy devices, capturing the sun’s rays and using this energy to extract carbon from the air and produce the carbohydrates on which most life on Earth—human as well as wild animals—depend. To many people, though, the nation’s plant life is regarded, if at all, as a green background, valued mainly for the habitat provided to wildlife, and the food, fuel, and fiber to people. Viewed more closely, this undifferentiated green mass explodes into a kaleidoscope of distinctive species, ranging from tiny “belly flowers” found in the southwestern deserts, to swaths of wild rhododendrons enlivening Appalachian mountaintops, to stately conifers overlooking Pacific Northwest coasts. In all, about 16,000 species of higher plants (known technically as “vascular” plants) are found in the United States, each with its distinctive habitat needs and life history requirements.
Insects and Invertebrates
For sheer number of species, however, insects dwarf all other groups of organisms, with more than 90,000 different types documented in the United States. These include such popular creatures as butterflies, which together with their moth and skipper relatives account for more than 12,000 U.S. species, as well as bees, whose more than 4,000 U.S. species are essential for pollination of wild flowers and cultivated crops alike. As the noted naturalist J. B. S. Haldane famously quipped, the creator must have “an inordinate fondness for beetles.” Indeed, with more than 25,000 U.S. species beetles are by far the most speciose group of insects, both in the United States and globally.
Largely unseen beneath the surface of our lakes, rivers, and streams, the nation’s freshwater fauna is truly extraordinary. By way of comparison, there are more species of freshwater fishes in a single river in Tennessee (the Duck), than are found on the entire European continent! A surprising number of freshwater groups reach their maximum diversity worldwide in the United States, including crayfishes, caddisflies, stoneflies, mayflies, and freshwater mussels.
No discussion of the diversity of life in the United States would be complete without at least a brief mention of the fascinating and unique flora and fauna of Hawaii. Having emerged as volcanos from the Pacific Ocean floor, the Hawaiian Islands are the most isolated large land mass in the world—about 2,500 miles separates the islands from the nearest continent. Because of this extreme isolation, relatively few plants and animals were able to naturally colonize the islands. Those that did, however, have evolved into one of the most distinctive and spectacular assemblages of species in the world.
The term endemic refers to species that are restricted to a single area. About 43% of Hawaii’s native vertebrate animals are endemic to the islands, as are 87% of its vascular plants, and 97% of its insects. The Hawaiian honeycreepers, a group of birds, illustrates the amazing evolutionary diversification that has occurred. From just one or at most two original colonists, more than 30 species of honeycreeper evolved, some with thick, parrot-like beaks specialized for cracking seeds while others developed long, curved beaks for sipping nectar.
- NatureServe Explorer
- USDA Plants
- Animal Diversity Web
- Encyclopedia of Life
- Precious Heritage: The Status of Biodiversity in the United States
More About Biodiversity
While some at-risk plants and animals gain formal legal protection under the Endangered Species Act, others are identified as imperiled through a system developed NatureServe and its network of state natural heritage programs. Bruce Stein outlines how both help us understand which species are thriving and which are declining, rare, or even already gone?