Occurring continuously all over the planet is the extermination of many populations through the paving over of their habitats. In 1880, the Sthenele Brown butterfly disappeared under the growing city of San Francisco. In 1943, the last of the small blue Xerces Butterfly was taken. It, too, then became extinct as San Francisco spread out over its sand-dune habitat. This butterfly is remembered today in the name of the Xerces Society, which is an organization dedicated to the preservation of endangered insects and invertebrates.
A large portion of the world is becoming more and more urbanized as time progresses. By 2025, east Asia is estimated to be 63% urbanized, Latin America 85%, and Africa 54%. Unless the right steps are taken to control suburban growth, many more populations and species are going to disappear under the concrete slabs of a city in the next half-century. Such species as the Attwater Prairie Chicken, which lived in the vicinity of Houston, Texas (United States) will vanish under further human expansion. Urbanization also removes entire ecosystems, because it tends to occur in areas that are both biologically rich and agriculturally productive. Plants and animals are usually attracted to areas that are well-watered and have moderate climates.
People have generally tended to settle and found their cities in such places also.
Urbanization's damage therefore tends to be concentrated in species-rich areas. In the USA alone, about 3 million acres per year are paved over or destroyed for urban development, highways, airports, and water projects.
One of the world's most species-rich areas is the Cape Province of South Africa, but that nation is undergoing a great population explosion that increases its population by 60,000 each month. The brilliant, sparkling yellow flowers of the Golden Gladiolus once covered a valley and hillside near Cape Town. But alien plants, introduced for a dune-reclamation scheme, escaped and smothered the populations of gladioli. A housing project that soon followed paved over most of the rest of the species' habitat, and the surviving plants were confined to a strip of land ten yards wide and forty yards long. They were then bulldozed for gravel. Amazingly, the few survivors were saved by being sandwiched between two rocky banks, but other factors - a
pathway, picnic sites, children's swings, beer cans, broken glass, and trampling - pressured it
further. Children also picked the beautiful flowers. In 1979 there remained 113 Gladiolus plants. In 1980 only 45 remained. Only two of those flowered; one was picked and dropped, and the other flowered early and produced two seed pods. The rest were seedlings. Their future is very dim.
There are other factors that also has its effects on plants and wildlife. Networks of roads that connect urban areas have impact on animals after construction is completed. Roads serve as barriers to movement, splitting apart herds of large animals or preventing them from making necessary seasonal migrations. The building of an Alaskan (United States) pipeline caused great concern over the movements of caribou and other wildlife. Smaller animals also suffer division of their populations by highways, railways, and canals. This changes their population structure and makes the remaining populations smaller and more vulnerable. A study has indicated that a four-lane divided highway may be to small forest mammals equivalent to a river twice as wide. Countless animals are also killed by cars every single day. When European frogs, toads, and salamanders cross roads in central Europe in great numbers, migrating to the lakes and streams where they breed, they are squashed in the millions. This problem is well known enough that European highway authorities have constructed fences to keep them off the roads. Fence-tunnel systems are also being considered to transfer the animals safely under highways in critical areas. The Swiss Association of Civil Engineers has even recently published instructions for constructing amphibian underpasses! Luckily for these creatures, the Swiss have learned to value their amphibian populations, a lesson that it would not hurt many of us to learn.