2. LOSS OF BIODIVERSITY
The colonisation of tropical pacific islands by human beings
has led to the extinction of more than two thousand species of
native birds .
The IUCN Red List(2004) document the extinction of 784
species in the last 500 that include 359 invertebrates, 338
vertebrates and 87 plants.
Some of the animals that have become extinct recently
include:
3.
4. More than 15,000 species worldwide are facing threat including 12
per cent of bird species, 23 per cent of all mammal species, 32 per
cent of all amphibian species and 31 per cent gymnosperm species.
Before humans appeared on Earth, there have been five episodes of
‘mass extinction’(i.e., loss of large number of species in a short time),
and ‘Sixth Extinction’ presently in process.
The current rate of species extinction is 100-1,000 times faster
than the pre-human times and our activities are responsible for the
faster rate.
5. •Loss of Biodiversity in a region can lead to the following:
i. Decline in plant production
ii. Lowered resistance to environmental perturbation
iii. Increased variability in ecosystem processes like water use,
pest/disease cycles, plant productivity, etc.
6. CAUSES OF BIODIVERSITY LOSSES
•There are four major causes(called “The Evil Quartet”) of biodiversity
losses:
Habitat loss and fragmentation
Over exploitation
Alien species invasions and
Co-extinction
7. HABITAT LOSS AND
FRAGMENTATION
•It is the most important cause of extinction, e.g.
•The tropical rain forests, once covering 14 per cent of the land surface of Earth, but now they cover only 6 per cent of the land area.
•The Amazonrainforests(calledthe‘lungsof theplanet’) are cleared for cultivation of soybeans or are converted into grasslands for
raising beef-cattle.
•The loss of a habitat deprives many animals and plants their homes and they face extinction.
•Degradation of many habitats by pollution threatens the survival of many species.
•When a large habitat is broken up into fragments, the population of mammals and birds with migratory habits or requiring large
territories are badly affected.
8. OVER-
EXPLOITATION
•When ‘need’ turns to ‘greed’, it leads to over-exploitation of natural resources; many species become extinct,
e.g.
•Steller ’s sea cow, passenger pigeon, many marine fishes became extinct due to over-exploitation by
humans.
9. ALIEN SPECIES INVASION
When alien species are introduced in an area, some of them become invasive and may cause extinction of indigenous
species,e.g.
Introduction of Nile Perch into Lake Victoria (East Africa) caused extinction of more than 200 species of Cichlidfish
in lake.
Invasive weed species such as Parthenium(carrot grass),Lantanaand Eichhorniawaterhyacinth) (causing
environmental damage and posing threat to our native species.
The illegal introduction of the Africancatfish(Clarians gariepenus) for aquaculture purposes, is posing threat to the
indigenous catfishes in our rivers.
