State of the States: Geographic Patterns of Diversity, Rarity, and Endemism

Abstract

The natural geography of the 50 states varies tremendously, supporting an equally varied suite of wild species—from flocks of tropical birds in southern Florida to caribou migrations across the Alaskan tundra. The geography of risk, too, varies across the nation, reflecting the interaction between natural and human history. Similarly, present-day land and water uses will largely determine the future diversity and condition of the flora and fauna. We can learn much, though, from looking at the current condition of a state’s biota, since this both reflects the past and helps illuminate the future. A state’s ecological complexion and the evolutionary history of its biota are the primary determinants of its biological diversity. These environmental factors have encouraged spectacular diversification in many regions: for instance, the freshwater fish fauna in the Southeast, the magnificent conifers along the Pacific cordillera, and the small mammal assemblages of the arid Southwest. Conversely, geological events such as the expansion and contraction of the ice sheets have left other areas of the country with a more modest array of species. States, however, are artificial constructs laid out on the landscape’s natural ecological patterns. While some state lines follow natural boundaries, such as shorelines or major rivers, most cut across the land with no sensitivity to natural features or topography. Nonetheless, urban and rural dwellers alike identify with the major ecological regions within which they live, and this is often the source of considerable pride. Montana is “big sky country,” referring to the vast open plains that sweep up against the eastern phalanx of the Rocky Mountains. California’s moniker “the golden state” now refers more to its tawny hills of summer—unfortunately at present composed mostly of alien species—than to the nuggets first found at Sutter’s Creek. Maryland, home of the Chesapeake Bay, offers the tasty blue crab (Callinectes sapidus) as its unofficial invertebrate mascot. The list could go on, evidenced by the growing number of states that offer vanity license plates celebrating their natural environment. Natural features have always played a dominant role in determining patterns of settlement and land use.