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Ecological crisis Generally, an ecological crisis occurs with the loss of adaptive capacity when the resilience of an environment or of a species or a population evolves in a way unfavourable to coping with perturbations that interfere with that ecosystem, landscape or species survival. It may be that the environment quality degrades compared to the species needs, after a change in an abiotic ecological factor (for example, an increase of temperature, less significant rainfalls). It may be that the environment becomes unfavourable for the survival of a species (or a population) due to an increased pressure of predation (for example overfishing). Lastly, it may be that the situation becomes unfavourable to the quality of life of the species (or the population) due to a rise in the number of individuals (overpopulation). Ecological crises vary in length and severity, occurring within a few months or taking as long as a few million years. They can also be of natural or anthropic origin. They may relate to one unique species or to many species, as in an Extinction event. Lastly, an ecological crisis may be local (as an oil spill) or global (a rise in the sea level due to global warming). According to its degree of endemism, a local crisis will have more or less significant consequences, from the death of many individuals to the total extinction of a species. Whatever its origin, disappearance of one or several species often will involve a rupture in the food chain, further impacting the survival of other species. In the case of a global crisis, the consequences can be much more significant; some extinction events showed the disappearance of more than 90% of existing species at that time. However, it should be noted that the disappearance of certain species, such as the dinosaurs, by freeing an ecological niche, allowed the development and the diversification of the mammals. An ecological crisis thus paradoxically favored biodiversity. Sometimes, an ecological crisis can be a specific and reversible phenomenon at the ecosystem scale. But more generally, the crises impact will last. Indeed, it rather is a connected series of events, that occur till a final point. From this stage, no return to the previous stable state is possible, and a new stable state will be set up gradually (see homeorhesy). Lastly, if an ecological crisis can cause extinction, it can also more simply reduce the quality of life of the remaining individuals. Thus, even if the diversity of the human population is sometimes considered threatened (see in particular indigenous people), few people envision human disappearance at short span. However, epidemic diseases, famines, impact on health of reduction of air quality, food crises, reduction of living space, accumulation of toxic or non degradable wastes, threats on keystone species (great apes, panda, whales) are also factors influencing the well-being of people. Due to the increases in technology and a rapidly increasing population, humans have more influence on their own environment than any other ecosystem engineer. Some common examples of ecological crises are: The Exxon Valdez oil spill off the coast of Alaska in 1989 Permian-Triassic extinction event 250 million of years ago Cretaceous–Tertiary extinction event 65 million years ago Global warming related to the Greenhouse effect. Warming could involve flooding of the Asian deltas (see also eco refugees), multiplication of extreme weather phenomena and changes in the nature and quantity of the food resources (see Global warming and agriculture). See also international Kyoto Protocol. Ozone layer hole issue Deforestation and desertification, with disappearance of many species. Volcanic eruptions such as Mount St. Helens and the Tunguska and other impact events The nuclear meltdown at Chernobyl in 1986 caused the death of many people and animals from cancer, and caused mutations in a large number of animals and people. The area around the plant is now abandoned by humans because of the large amount of radiation generated by the meltdown. Twenty years after the accident, the animals have returned. African Elephant The Elephants of the genus Loxodonta, known collectively as African elephants, are currently found in 37 countries in Africa. African elephants are distinguished from Asian elephants in several ways, the most noticeable being their ears. Africans' ears are much larger. The African is typically larger than the Asian and has a concave back. Both African males and females have external tusks and are usually less hairy than their Asian cousins. African elephants have traditionally been classified as a single species comprising two distinct subspecies, namely the savanna elephant (Loxodonta africana africana) and the forest elephant (Loxodonta africana cyclotis), but recent DNA analysis suggests that these may actually constitute distinct species. While this split is not universally accepted by experts a third species of African elephant has also been proposed.[14] Under the new two species classification, Loxodonta africana refers specifically to the Savanna Elephant, the largest of all elephants. In fact, it is the largest land animal in the world, standing up to 4 m (13 ft) at the shoulder and weighing approximately 7,000 kg (7.7 tons). The average male stands about 3 m (10 ft) tall at the shoulder and weighs about 5500–6000 kg (6.1–6.6 tons), the female being much smaller. Most often, Savanna Elephants are found in open grasslands, marshes, and lakeshores. They range over much of the savanna zone south of the Sahara. The other postulated species is the Forest Elephant (Loxodonta cyclotis). Compared with the Savanna Elephant, its ears are usually smaller and rounder, and its tusks thinner and straighter and not directed outwards as much. The Forest Elephant can weigh up to 4,500 kg (10,000 lb) and stand about 3 m (10 ft) tall. Much less is known about these animals than their savanna cousins because environmental and political obstacles make them difficult to study. Normally, they inhabit the dense African rain forests of central and western Africa, though occasionally they roam the edges of forests and so overlap the territories of the Savanna elephants and breed with them. In 1979, Iain Douglas-Hamilton estimated the continental population of African elephants at around 1.3 million animals.his estimate is controversial and is believed to be a gross overestimate, but it is very widely cited and has become a de facto baseline that continues to be incorrectly used to quantify downward population trends in the species. Through the 1980s, Loxodonta received worldwide attention due to the dwindling numbers of major populations in East Africa, largely as a result of poaching. Today, according to IUCN’s African Elephant Status Report 2007[ there are approximately between 470,000 and 690,000 African elephants in the wild. Although this estimate only covers about half of the total elephant range, experts do not believe the true figure to be much higher, as it is unlikely that large populations remain to be discovered.[18] By far the largest populations are now found in Southern and Eastern Africa, which together account for the majority of the continental population. According to a recent analysis by IUCN experts, most major populations in Eastern and Southern Africa are stable or have been steadily increasing since the mid-1990s, at an average rate of 4.5% per annum. Elephant populations in West Africa, on the other hand, are generally small and fragmented, and only account for a small proportion of the continental total. Much uncertainty remains as to the size of the elephant population in Central Africa, where the prevalence of forest makes population surveys difficult, but poaching for ivory and bushmeat is believed to be intense through much of the region. In South Africa, the elephant population has tripled, growing from 8,000 in 1995 to more than 20,000 by 2008. As a result of this growing population, South Africa has announced the lift of a ban introduced in 1995 that made it illegal to kill elephants. This has sparked controversy among environmental groups.