Monday, September 5, 2011

Invasive species

Every year, new animal and vegetal species are included in the Red List of Threatened Species.
There have already been five major extinction events in our planet and it seems that the sixth is on-going. The first five extinctions were not our fault (basically because we did not exist yet) but it seems that we are to blame for this sixth extinction event.
However, this post is not about the threatened species, but just the opposite: the so-called invasive species. Because of us, these threatening species are developing too much, to the point that they threaten the biodiversity of our planet. Not so long ago, oceans and mountains were natural borders preventing some species of flora and fauna from spreading around the Earth (or at least making it really difficult). However, this is no longer so. Some species, with our help, have invaded new ecosystems to the point that they threaten the rest of species and the whole ecosystem itself.
To raise awareness about the significance and complexity of such invasions, the Invasive Species Specialist Group (ISSG), under the auspices of the International Union for Conservation of Nature (IUCN), draws a list with one hundred invasive species threatening biodiversity. This list is not fully-comprehensive list, and the listed species are not even the most dangerous ones either, but there are one hundred illustrative examples of varied nature. Absence from the list does not imply that a species poses a lesser threat.
This list should be compulsory reading material at school, not only to let people know the name of these one hundred species, but also to make people realise that it is very easy to destroy an ecosystem, even if we have good intentions.
Let’s see a couple of examples to better illustrate this post.
- In the 1950s, due to an overfishing in the Lake Victoria, the Nile perch was introduced. Native fish was traditionally sun-dried but the Nile Perch has a higher fat content so it needs to be smoked (increasing firewood demand), resulting in a deforestation of nearby woods. This deforestation caused soil erosion and greater residues sedimentation into the lake, which in turn resulted in an invasion of waterweed and water hyacinths –the later is also included in that list. Outcome: more than 200 fish and plant species have disappeared from this lake, and perch and hyacinths colonized the whole place.
- The read-eared slider turtle has recently become the most common marketed water turtle kept as pet. Indeed, you guess it right: we are talking about those little cute turtles we see in many aquariums. But when people get tired of it, the turtle is released into the drains (or into a river, for those cases of sensitive people). And the rest goes without saying: these turtles can transmit diseases and, on top of that, they are omnivorous so they predate small invertebrates and plants in the ecosystem –the same invertebrates and plants which feed other species, thus affecting the whole ecosystem.
Besides these two examples, the list also includes wild board, deer, rabbit, five species of ants, giant toad, Australian blackwood, maritime pine or mussel. When reading through this list, however, there is only one species missing: us.


  1. UICN’s red list of threatened species:
  2. Major extinction events:
  3. About invasive species:
  4. Invasive Species Specialist Group (ISSG) by UICN:
  5. International Union for Conservation of Nature (IUCN):
  6. List of the 100 World's Worst Invasive Alien Species:
  7. Nile perch:
  8. Water hyacinth:
  9. Red-eared slider:

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