Download Ecological crisis

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.