Humans probably evolved as group hunters, whose social cooperation and tool-making skills enabled them to exploit large prey species. Hunting technology became increasingly effective over time and according to the so-called Pleistocene Overkill Hypothesis contributed to the decline and extinction of large mega-fauna worldwide. For example, more than half of the large land mammal biota of the Americas disappeared when humans first colonized the continent in the Late Pleistocene, around 15 000 years ago. This dramatic event, unparalleled in the deeper fossil record and unmatched in other continents at the same time, was later replicated with the arrival of humans in New Zealand, the Pacific Islands, Madagascar, and the Caribbean. It has been argued that the overexploitation of large prey species motivated the invention of agriculture, that is, the historic shift from exploitation of wild resources to the production of domesticated species. Despite the enormous success of agriculture, however, exploitation of wild resources has intensified throughout recent history, particularly in the world's forests and oceans.
As populations of land mammals were depleted by human hunters, exploitation of aquatic species by fishermen spread from lakes and rivers to estuaries and the coastal ocean. Coastal oceans showed signs of severe depletion 500 years ago, when fishing spread to shelf seas, such as the Central North Sea and the Canadian Grand Banks. Just over 50 years ago, fishing moved to the open ocean and quickly reached global coverage. Only in the last 15 years as other resources were depleted, has the deep sea (areas below 1000 m depth) been targeted on a large scale for fisheries exploitation.
Exploitation of wild land animals has ceased to be a major source of food supply in industrialized countries, but continues to be important in many developing countries. Rapidly increasing human populations, improved hunting technology, and accessibility of remote areas, however, have recently led to a crisis situation, particularly in Africa, where exploitation of wild animals is estimated to exceed the maximum sustainable yields by 6 times. The wild meat (or 'bushmeat') trade includes large rodents, antelopes, and apes, among other species, and is now threatening many species with extinction. Large species, such as tapirs or primates, tend to disappear first and, as they vanish, people turn to hunting smaller ones, such as squirrels or cane rats. This species loss has consequences for both forest dynamics and rural people.
Exploitation of forest tree resources has also intensified in recent decades. Forests cover about one-quarter of the world's land surface, excluding Greenland and Antarctica. Just over half are found in developing countries. Exploitation of forest tree resources has increased throughout human history, as our population and the demand for wood fuel and building material grew. Large-scale deforestation was already evident in India, China, and the Mediterranean 2000-3000 years ago. Some areas, such as parts of Italy, have never recovered their native forest cover since. Globally, 20-50% of formerly forested areas have lost their tree cover. While forest cover in developed countries has now stabilized and is slightly increasing overall, rapid deforestation continues in many developing countries, particularly in the tropics. The estimated net annual change in forest area worldwide during 1990-2000 was -9.4 million ha yr-1.
Today, exploitation of wild animals and plants is occurring on an unprecedented scale, and has affected every ecosystem on Earth, including, most recently, the deep sea. Annual rates of exploitation are in the range of 3400 million m3 of wood (including plantations), 100 million tons of marine fish, 9 million tons of freshwater fish, and probably around 5 million tons of wild meat per year (Table 1). Less than 8% of global forest area and less than 1% of the global ocean is legally protected from exploitation. Because of the long history and current scale of exploitation, no place can be considered pristine and many ecosystems have been completely transformed by exploitation. Exploitation is probably the foremost cause of recent extinctions; however, its effects are often compounded by habitat destruction. Many populations of large vertebrates, both on land and in the ocean, are currently threatened by overexploitation. Prominent examples include many sharks, great apes, and large reptiles. There are a number of positive examples as well, where exploitation has remained sustainable for hundreds of years (Gulf of Maine lobster fishery for example), where formerly depleted resources have recovered (rebounding of over-exploited beaver populations in the nineteenth-century Canada, elephants in late twentieth-century Africa), and destructive management practices have been replaced by sustainable ones (selective tree harvesting in Scandinavia). These successes are important in informing ecologists and resource managers about the conditions that are required to achieve sustainable exploitation.
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