tailieunhanh - Freeland - Molecular Ecology (Wiley, 2005) - Chapter 7

7 Conservation Genetics The Need for Conservation Biodiversity quite simply refers to all of the different life forms on our planet, and includes both species diversity and genetic diversity. There are many reasons why we value biodiversity, the most pragmatic being that ecosystems. | 7 Conservation Genetics The Need for Conservation Biodiversity quite simply refers to all of the different life forms on our planet and includes both species diversity and genetic diversity. There are many reasons why we value biodiversity the most pragmatic being that ecosystems which maintain life on our planet cannot function without a variety of species. On a slightly less dramatic note different species provide us with food crops livestock fibres wool cotton pharmaceuticals 25 of medical prescriptions in the USA contain active ingredients from plants Primack 1998 and entertainment countryside walks ecotourism zoos gardening fishing birdwatching . From a less anthropocentric perspective species may be considered worthwhile in their own right and not simply because they benefit humans in which case there are important ethical considerations surrounding the predilection of one species Homo sapiens to drive numerous other species extinct. We know from the fossil record that biodiversity has been increasing steadily over the past 600 million years despite the fact that as many as 99 per cent of species that have ever lived are now extinct Figure . Around 96 per cent of all extinctions have occurred at a fairly constant rate creating what is known as the background extinction rate. This has been estimated from the fossil record as an average of 25 per cent of all living species becoming extinct every million years Raup 1994 . The remaining 4 per cent or so of all extinctions occurred during five separate mass extinctions which are identified from the fossil record as periods in which an estimated 75 per cent or more of all living species became extinct. The most recent and also the most famous mass extinction occurred in the late Cretaceous 65 million years ago when approximately 85 per cent of all species including the dinosaurs were wiped out. Many biologists predict that we are now entering a sixth mass extinction Leakey and Lewin 1995 . Over the past 400 .