1.1 Significant cause of the extinction of hundreds
of species and the endangerment of many
more, such as whales and many African large
mammals. Most extinctions over past several
hundred years are mainly due to
over-harvesting for food, fashion, and profit.
1.2 Commercial hunting
1.2.1 Pet and decorative plant trade.
18.104.22.168 $5 billion, with perhaps 1/4 to 1/3 of it illegal.
1.3 The Black
1.3.1 During the colonization of Africa in the early 20th
century, rhinos were considered vermin and were
exterminated at all costs. The European hunters of
that period are responsible for the early decline of
black rhino populations.
1.3.2 Between 1970 and 1992, 96% of
Africa’s remaining black rhinos were
killed, primarily for their horns.
22.214.171.124 Some rhino horns can sell
for up to $100,000.
1.3.3 Political instability and wars have greatly
impeded rhino conservation work in Africa.
126.96.36.199 A recent increase in poaching in South Africa
threatens to erase any advances in
conservation made in recent decades.
2 Loss of habitat
2.1 The Tropical Rainforest
2.1.1 Harbour at least 50%, and perhaps more,
of world's biodiversity.
2.1.2 The original extent of tropical rain
forests was 15 million km2. Now there
remains about 7.5-8 million km2
2.1.3 The current rate of loss is estimated at near 2%
annually (100,000 km2 destroyed, another 100,000
km2 degraded). While there is uncertainty regarding
the rate of loss, and what it will be in future, the
likelihood is that tropical forests will be reduced to
10-25% of their original size by late 21st C.
2.1.4 The Amazon
188.8.131.52.2.1 Increasing global demand for food, especially
meat, has led to Brazil becoming the world’s
biggest beef exporter, and the second-largest
exporter of soybeans, which are mainly used
for livestock feed. Forests are often cleared to
make way for grazing land or soya plantations.
184.108.40.206.3 Climate change
220.127.116.11.3.1 The Amazon is at the core of climate concerns – not only
because the burning and destruction of forests adds to the
amount of CO2 in the atmosphere, but also because the
rainforest itself is vulnerable to global warming. This can
create a ‘negative feedback loop’ – the more forest that’s
lost, the more the temperature rises, which causes more
forest to die back, and so on.
2.2 Habitat/ecosystem Fragmentation
2.2.1 The forest, meadow, or other habitat that remains generally is in small,
isolated bits rather than in large, intact units. Each is a tiny island that
can at best mai ntain a very small population. Environmental
fluctuations, disease, and other chance factors make such small isolates
highly vulnerable to extinction. Any species that requires a large home
range, such as a grizzly bear, will not survive if the area is too small.
2.2.2 Can be caused by Mining, ranching/overgrazing, and
developing of roads and paths for increases in tourism
(more people means more trampling and erosion).
3 Invasion of non-native species
3.1 Of all documented extinctions since 1600, introduced
species appear to have played a role in at least half.
3.2 Some species change the habitat which
some species are dependent on.
3.2.1 When the Asian chestnut blight fungus virtually eliminated American chestnut from over 180 million acres of eastern
United States forests in the first half of the 20th century, it was a disaster for many animals that were highly adapted to
live in forests dominated by this tree species. For example, ten moth species that could live only on chestnut trees
3.3 Some species hunt others to extinction
3.3.1 The predatory brown tree snake, introduced in cargo from the Admiralty Islands,
has eliminated ten of the eleven native bird species from the forests of Guam.
3.3.2 The first sailors to land on the remote Atlantic island of
St. Helena in the 16th century introduced goats, which
quickly extinguished over half the endemic plant species.
3.4 Some species out compete
others for resources.
3.4.1 North American gray squirrels are driving native red
squirrels to extinction in Great Britain and Italy by
foraging for nuts more efficiently than the native
species. Such competition for resources is not easy
to observe, but the end result is the loss of a native
3.5.1 Hybridization, or cross-breeding, of introduced species with natives gradually leads
to the extinction of many native species, as their gene pools inevitably evolve to
become those of the invader. Introduced mallards, for instance, are driving the
native Hawaiian duck to a sort of genetic extinction by breeding with them.
4 Over fishing/Harmful fishing
4.1 In just 55 years, humans have managed to wipe out 90 percent
of the ocean’s top predators. These are animals like sharks,
bluefin tuna, swordfish, marlin, and king mackerel.
4.1.1 According to Greenpeace, the depletion of these top predator
species can cause a shift in entire oceans ecosystems where
commercially valuable fish are replaced by smaller,
plankton-feeding fish. This century may even see bumper crops
of jellyfish replacing the fish consumed by humans.
4.2 Harmful methods
4.2.1 Bottom trawling - Ships drag huge, heavy nets held open by doors, many of
which weigh several tons each, over the seafloor to catch fish that dwell near the
bottom of the ocean. In the process, they destroy everything else, including deep
sea coral and sponges, and other sensitive seafloor life.
4.2.2 Cyanide fishing: In this technique, fishers squirt
sodium cyanide into the water to stun fish without
killing them, making them easy to catch.
18.104.22.168 For every live fish caught using cyanide, a
square meter of their coral reef is killed.
4.2.3 Dynamite fishing: In this technique, dynamite or other explosives
are set off under water. The dead fish floating to the surface are
then simply scooped up. The explosives completely destroy the
underwater environment, leaving it as rubble.