The major rush of extinctions under way in tropical rain forests is caused by habitat loss, habitat fragmentation, and overexploitation of species useful or threatening to humans. As burgeoning human populations continue to claim an ever greater share of the world’s renewable resources, intensification of land use will make it increasingly difficult to maintain biodiversity outside of strictly protected nature preserves. Further, because many species can maintain themselves only in large expanses of unaltered or lightly disturbed habitat, fully protected areas should remain the cornerstone of any conservation strategy that aims at minimizing the loss of tropical biodiversity. We have identified five principal forces of extinction in a humandominated world: deforestation, habitat fragmentation, overkill, secondary extinction, and introduced species. In this chapter, we briefly review the manner in which each of these processes contributes to extinction, both as isolated forces and in synergism with other forces. Our conclusion is that all five forces of extinction can be minimized by retaining intact natural habitat in the largest possible blocks. As the human population continues to expand, it is inevitable that most land outside strictly protected nature preserves will be subject to increasingly intensive use, resulting in decreased biodiversity. We therefore argue that maintaining biodiversity can best be achieved through development planning at the largest practical spatial scales. Parks should be as large as possible, designed to benefit from passive protection (inaccessibility), and rigorously protected. Only through major strengthening of institutions responsible for park protection can we expect to see tropical biodiversity survive the coming century. The earth is experiencing an extinction crisis because the human population is increasing rapidly and laying claim to an ever larger share of land and resources. Simultaneously, nearly all individual humans fervently desire to increase their level of material well-being. The resulting double impetus for rapid economic expansion generates exponentially increasing demands for most renewable and nonrenewable resources. The world is consequently experiencing a wave of nonsustainable use of most basic, life-supporting resources, including soil, groundwater, forests, grasslands, and fisheries. The earth’s population today is 5.5 billion, and it is increasing by more than 90 million per year.
Innovation and the growth of human population
