RELATIONSHIP BETWEEN SPECIES DIVERSITY AND ECOSYSTEM
Most of the ecologists believe that
·
The communities with more species are more
stable than those with lesser species.
·
The stable community means lesser variations in
productivity from year to year.
·
The community with more species, is more
resistant to occasional (natural or man-made) disturbances.
·
Such communities are resistant to invasions by
alien or exotic species.
David Tilman, in his long-term ecosystem experiments,
found that plots with more species showed less - year to year variation in total
biomass and the increased diversity
contributed to higher productivity. Thus the rich biodiversity is not only essential for the health of the
ecosystem but also for the survival of human race on this planet.
Loss of Biodiversity
There is continuous loss of the earth' treasure of species.
For example, the colonization of tropical pacific Islands by human has led to
extinction of more than 2000 species of native birds.
The Red
list of lUCN documented the extinction of 784 species in last 500 years. The
last 20 years witnessed the disappearance of 27 species.
Some important examples of recent extinctions are
Dodu (Mauritius), Quagga (Africa), Thylacine
(Australia). Steller Sea-cow (Russia), and
subspecies of Tiger, like bali, javan and caspian.
·
Presently, more than 15,500 species world-wide
are facing the threat of extinction.
·
This includes 32% of amphibian species, 23% of
mammalian species and l2% of birds’ species.
·
About 31% of the gymnosperms species are also
facing the extinction. The amphibians are however,more vulnerable in such
cases.
From origin to evolution of life on earth, i.e. duration
about 3 billion yrs., there have been 5-episodes of mass extinction, but the
present, the 6‘*‘, mass extinction is 100 to l000 times fasterthan the
pre-human extinctions.
The ecologists now warn that-in next l00 years about 50% of all
the species on earth will be wiped out. The loss in biodiversity of a region
leads to
1. Lowered resistance to environmental changes
2. Decline in the plant production
3, Increased variability in certain ecosystem, pest disease
cycles and water use etc.
Causes of loss of Biodiversity
The accelerated rate of species-extinction is largely due to
human activities. There are 4-major causes, called ‘The Evil Quartet’, for
the loss of biodiversity -
l. Habitat loss and fragmentation
2. Overexploitation
3. Invasion of Alien or exotic species
4. Co-extinctions
·
Habitat loss and fragmentation
The cutting trees and burning of forest destroys the natural
habitat of a species. The construction of mines, dams, harbors, industries and
buildings for human settlement has also affected the biodiversity. The Habitat
destruction is the primary and major reason for the loss of biodiversity.
The tropical rain forest is the example of the habitat loss
where forest covering has been reduced from 14% of land surface to 6%.
The Amazon rain forest, called ‘The Lungs of the Planet ',
which harbors millions of species, is being cleared for cultivating soybean or
developing grasslands for raising cattle. The pollution is also the factor for
degradation of habitat.
When large habitats are broken into small fragments due to
various human activities, the population of migratory animals, mammals and
birds, that require a large territory, are adversely affected.
·
Overexploitation
In ecology, overexploitation
describes one of the five main activities threatening global biodiversity. Overexploitation can lead to resource
destruction, including extinctions. Many marine fishes are also being over harvested. Over
fishing from a water body, or over harvesting a product is
just like ‘killing a
goose laying golden eggs '.
.
·
Invasion
of Alien or exotic species
When alien species are
introduced into an explored area, some of the species turn invasive and cause
decline or extinction of indigenous species.
For example –
Introduction of Nile perch into lake Victoria (E. Africa) led to
the extinction of more than 200 species of Cichlid fish in the lake
Introduction of weed species, like Carrot grass (Parrhenium),
Lantana and water hyacinth (Eicchornia) has posed threat to the native
species and damage to environment.
The illegal
introduction of African cat fish (Clarias gariepinus) for aquaculture purposes
into the river has threatened indigenous cat fishes.
·
Co-extinctions
Whenever a plant or
animal species becomes extinct, its obligatory-associated species also becomes
extinct. For example, when a host species becomes extinct, the parasite also meets
the same fate. In case of ‘plant pollinator mutualism ' the extinction of one
species leads to the extinction of the other.
Process of extinction of biodiversity
1. Natural extinction -
With the change of
environmental conditions some species have disappeared and the more adaptive
species have appeared. This extinction
is slow and is called ‘Background extinction’.
2. Mass extinction –
lt is extinction of large
number of species due to natural calamities/catastrophes. The extinction of
Dinosaurs is one such example.
3. Anthropogenic extinction -
It is the
disappearance of species due to human activities. This man-made extinction represents
a severe depletion of biodiversity in terms of time. The current rate of
extinction is thousand times higher than the background extinction.
If the
current rate of losses continues the earth may lose up to 50% of the species by
the end of 2 l “Century.
Susceptilibility to extinction
-
The species with the
following features are more susceptible (vulnerable) to extinction than the
other species.
l. Larger body size
(eg. Elephant, Bengal Tiger and Lion etc.)
2. Smaller population
with low reproductive rate (eg. Blue whale and Giant panda)
3. Fixed habitat or
migratory routes (eg. Whooping cranes and Blue whales).
4. Feeding at higher
trophic level in the food chain, (eg. Bengal tiger and Bald Eagle).
5. Narrow range of
distribution (eg. Island species and woodland caribou).
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