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Local threats to biodiversity

Over hunting
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.
2. Commercial hunting
  1. Pet and decorative plant trade.
    1. $5 billion, with perhaps 1/4 to 1/3 of it illegal.
3. The Black Rhino
  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.
  2. Between 1970 and 1992, 96% of Africa’s remaining black rhinos were killed, primarily for their horns.
    1. Some rhino horns can sell for up to $100,000.
  3. Political instability and wars have greatly impeded rhino conservation work in Africa.
    1. A recent increase in poaching in South Africa threatens to erase any advances in conservation made in recent decades.
Loss of habitat
1. The Tropical Rainforest
  1. Harbour at least 50%, and perhaps more, of world's biodiversity.
  2. The original extent of tropical rain forests was 15 million km2. Now there remains about 7.5-8 million km2
  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.
  4. The Amazon
    1. Causes
      1. Deforestation
      2. Expanding agriculture
        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.
      3. Climate change
        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. Habitat/ecosystem Fragmentation
  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. Can be caused by Mining, ranching/overgrazing, and developing of roads and paths for increases in tourism (more people means more trampling and erosion).
Invasion of non-native species
1. Of all documented extinctions since 1600, introduced species appear to have played a role in at least half.
2. Some species change the habitat which some species are dependent on.
  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 became extinct.
3. Some species hunt others to extinction
  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.
  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.
4. Some species out compete others for resources.
  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 species.
5. Hybridisation
  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.
Over fishing/Harmful fishing
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.
  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.
2. Harmful methods
  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.
  2. Cyanide fishing: In this technique, fishers squirt sodium cyanide into the water to stun fish without killing them, making them easy to catch.
    1. For every live fish caught using cyanide, a square meter of their coral reef is killed.
  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.
    1. The firth of clyde

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Local threats to biodiversity

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	Created by Jason Edwards-Suarez over 8 years ago