Threats to Biodiversity

Over the last century, humans have come to dominate the planet. Our rapidly expanding population and economies place increasing demands on the world's resources. One-third to one-half of the world's terrestrial surface has been substantially altered by human activity (Vitousek et al., 1997). Many species persist on a greatly reduced area of their former range and on increasingly fragmented landscapes. Ecosystems suitable for agriculture, such as tropical dry forests and tall-grass prairie, have almost completely disappeared from our planet. Dams are disrupting freshwater ecosystems, while the marine world is threatened by overfishing and habitat destruction. Humans are also transporting plants and animals around the globe both deliberately and unintentionally. These "invaders" threaten other species or change entire ecosystems. David Quammen (1998) aptly notes that we are living on an increasingly "weedy planet," filled with species that can survive only in human-modified landscapes. Human influence reaches even the farthest corners of the globe; species in the Arctic and Antarctic are contaminated by pollutants created thousands of miles away and carried through the atmosphere. We are even modifying the functioning of the entire planet, changing the earth's atmosphere through the industrial release of carbon dioxide (which may dramatically change the earth's climate) and diminishing the ozone layer through the production of chlorofluorocarbons.

Only by understanding the principal threats to biodiversity can we hope to meet the challenge of conserving biodiversity. Direct threats to biodiversity are relatively straightforward. They include habitat fragmentation, invasive species, pollution, overexploitation, and global climate change. The underlying causes of biodiversity loss, on the other hand, are often more complex and stem from many interrelated factors. The most important of these are overpopulation and overconsumption, which are compounded by social, economic, and political forces. Existing socioeconomic structures and policies contribute to biodiversity loss or hinder conservation efforts by reducing incentives to conserve. Furthermore, weak governance structures, policies, and legislation, coupled with corruption and a lack of enforcement, often exacerbate the threats to biodiversity.

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