Sharing the Planet: Can Humans and Nature Coexist? - effects of urban growth

USA Today (Society for the Advancement of Education), Jan, 1999 by John Tuxill, Christopher Bright

Mammals in most regions have been less susceptible than birds to invasive species, but there is one big exception--the unique marsupial and rodent fauna of Australia, long isolated from other continents. The introduction of non-native rabbits, foxes, cats, rats, and other animals has combined with changing land use patterns during the past two centuries to give Australia the world's worst modern record of mammalian extinction.

Reptiles in retreat

Among reptiles, species are declining for reasons similar to those affecting birds and mammals. Habitat loss is again the leading factor, contributing to the decline of 68% of all threatened reptile species. In island regions, habitat degradation has combined with exotic species to fuel the decline of many unique reptiles. In Ecuador's Galapagos archipelago, the largest native herbivores are reptiles--long-isolated giant tortoises and land and marine iguanas found nowhere else in the world. Introduced goats are winning out over the native reptiles, however, and these interlopers have eliminated unique populations of tortoises on three of 14 islands within the Galapagos chain. At least two other tortoise populations are in imminent danger.

In addition, 31% of threatened reptiles are affected directly by hunting and capture by humans. This figure may be somewhat inflated since the reptile groups most thoroughly assessed--turtles and crocodilians--are among those most pursued by humans. Nevertheless, the high percentage is a clear indication of the heavy exploitation suffered by these species.

The plight of sea turtles has been studied and publicized since at least the 1960s, and all seven species are judged to be endangered, with many populations continuing to dwindle. Although there has been progress on protecting sea turtles at some of their best-known nesting grounds, illegal poaching for meat and eggs remains a widespread problem. Where beaches are lit at night with artificial lights, as at tourist resorts, hatchling turtles become disoriented and crawl toward the land rather than the sea. Moreover, sea turtles continue to suffer inadvertent, but significant, mortality from nets set for fish and shrimp.

Although less well-known than their seagoing relatives, tortoise and river turtle species are exploited intensively in certain regions, to the point where many populations are depleted greatly. Tortoises and river turtles throughout Southeast Asia long have been an important source of meat and eggs for local residents. There is a burgeoning international trade in these species to China, where they are used in traditional medicine.

Certain species of crocodilians still suffer from overhunting (such as black caimans in the Amazon Basin) and from pollution (such as the Indian gharial and the Chinese alligator), but this is one of the few taxonomic groups of animals whose over-all fate actually has improved over the past two decades. Since 1971, seven alligator and crocodile species have been taken off the endangered list, including Africa's Nile crocodile and Australia's huge estuarine crocodile. In part, these recoveries are due to the development of crocodile ranching operations that harvest the animals for their meat and hides. When combined with effective wildlife protection efforts, this can take hunting pressure off wild populations.