ABSTRACT
The leading sources of today's species loss habitat alteration, invasions by exotic species, pollution, and over hunting are all a function of human activities. Habitat is also lost to agriculture, as population growth increases the demand for food. Ten percent of the world's land area is now dedicated to crops; most of that land has been stripped of the species diversity that characterized its wild state. Genes from wild varieties are used to give cultivated varieties desired characteristics such as resistance to pests, drought, or disease. Growth in human travel and commerce explains many accidental invasions by exotics, but foreign species are also deliberately introduced into gardens, plantation forests, and aquaculture systems. To the extent that greenhouse gases induce changes in global climate, many species may be at risk as habitats shift or shrink, and as some life forms, such as insects or animals, adapt and migrate more quickly than others, such as plants.
