Importance of Species Diversity to the Ecosystem
(i) According to ecologists, communities with more species tend to be more stable than those with less species.
(ii) Attributes of a stable community are;
(a) It should not show too much variation in productivity from year to year.
(b) It must be either resistant or resilient to occasional disturbances (natural or man made).
(c) It must be resistant to invasions by alien species.
(iii) David Tilman’s longterm experiments on ecosystem found that plots with more species showed less year-to-year variation in total biomass. He also showed that increased diversity contributed to higher productivity.
(iv) It is not clear how species richness contributes to the well-being of an ecosystem. But, it is enough to realise that rich biodiversity is not only essential for ecosystem health but imperative for the survival of the human race on this planet.
(v) Paul Ehrlich through his rivet popper hypothesis tried to explain the importance of biodiversity for the survival of species.
(a) The hypothesis assumes the ecosystem to be an airplane and the species to be the rivets joining all parts together.
(b) If every passenger pops a rivet to take home (resulting in species extinction), it may not affect the flight safety initially (proper ecosystem functioning) but with time as more and more rivets are removed, the plane becomes dangerously weak.
(c) Loss of rivet on the wings (key species that drives major ecosystem functions) is a more serious threat to flight safety than loss of a few rivets on the seats or windows of the plane.
vi) Loss of biodiversity is caused by the over population, urbanisation and industrialisation.
(i) The colonisation of tropical Pacific Islands by humans have led to the extinction of more than 2,000 species of native birds.
(ii) The IUCN Red list (2004) documents the extinction of 784 species (including 338 vertebrates, 359 invertebrates and 87 plants) in the last 500 years.
(iii) Some latest examples of recent extinctions are dodo (Mauritius), Quagga (Africa), Thylacine (Australia), Steller’s sea cow (Russia) and three sub-species (Bali, Javan and Caspian) of tiger.
(iv) The last twenty years alone have witnessed the disappearance of 27 species.
(v) Presently, 12% of bird species, 23% of all mammal species, 32% of all amphibian species and 31% of all gymnosperm species in the world face the threat of extinction.
(vi) Careful analysis of records shows that amphibians appear to be more vulnerable to extinction.
(vii) The grim scenario of extinctions is the fact that more than 15,500 species world wide are facing the threat of extinction.
Results of Loss of Biodiversity in a Region
(a) Decline in plant production.
(b) Lowered resistance to environmental perturbations, such as drought.
(c) Increased variability in certain ecosystem processes such as plant productivity, water use, pest and disease cycles.
Causes of Biodiversity Losses
These are mainly four as given below. They are also named as The Evil Quartet.
(i) Habitat Loss and Fragmentation
(a) The main cause of extinction of species is the destruction of their habitat
(b) Examples,
• Tropical rainforests once covering more than 14% of the land surface, now cover only 6% of land area.
• Amazon rainforest (called lungs of the planet) is being cut and cleared for the cultivation of soybeans and for conversion to grasslands for raising beef cattle.
(c) When large habitats are broken up into small fragments due to various human activities, mammals and birds requiring large territories and certain animals with migratory habits are badly affected, leading to their population decline.
(d) The degradation of many habitats by pollution also threatens the survival of many species, many have extincted in last 500 years.
(ii) Over-exploitation of natural resources by humans results in degradation and extinction of the resources. For example, Steller’s sea cow, passenger pigeon and many marine fishes have extincted in last 500 years.
(iii) Alien (exotic) Species Invasions
When alien (exotic) species are introduced unintentionally or deliberately, some become invasive and cause harmful impact resulting in extinction of the indigenous species. Examples,
(a) Nile perch a large predator fish when introduced in Lake Victoria (East Africa) caused the extinction of an ecologically unique species of cichlid fish in the lake.
(b) Invasive weed species like Parthenium (carrot grass), Lantana and Eichhornia (water hyacinth) caused environmental damage and pose threat to native species.
(c) The recent example is of the African cat fish (Clarias gariepinus) introduced for aquaculture purpose, is posing a threat to the indigenous cat fishes of Indian rivers.
(iv) Co-extinctions When a species become extinct, the plant and animal species associated with it in an obligatory manner, also become extinct. For example, if the host species becomes extinct, all those parasites exclusively found on it will also become extinct. In plant pollinator mutualism, extinction of one results in the extinction of the other.
Biodiversity Conservation
Reasons of conserving biodiversity is grouped into three categories
- Narrowly Utilitarian
- Broadly Utilitarian
- Ethical
Narrowly Utilitarian
Humans derive countless direct economic benefits from nature such as cereals, pulses, fruits, firewood, fiber, construction material, industrial products like tannins, lubricants, dyes, resins, and perfumes.
Fig. human beings derive pulses, firewood, dyes from nature
Broadly Utilitarian
- Biodiversity plays a major role in many ecosystem services that nature provides.
- Amazon forest is estimated to produce, through photosynthesis, 20 per cent of the total oxygen in the earth’s atmosphere
- Bees, bumblebees, birds and bats pollinate the flowers without which plants cannot give us fruits or seeds.
Ways to Conserve Biodiversity
- Biodiversity can be conserved by In Situ and Ex Situ conservation.
- The process of protecting biodiversity at all levels by conserving and protecting the whole ecosystem is called in situ conservation.
- The process in which endangered and threatened animals are saved by taking urgent measures is called ex situ conservation.
- Biodiversity hotspots are the regions with very high levels of species richness and high degree of endemism.
- Three hotspots – Western Ghats and Sri Lanka, Indo-Burma and Himalaya – cover high biodiversity regions.
Fig. western Ghats and Himalaya
- Biodiversity-rich regions are legally protected as biosphere reserves, national parks and sanctuaries.
- India now has 14 biosphere reserves, 90 national parks and 448 wildlife sanctuaries.
- Sacred groves are the forests in which tracts of forest were set aside, and all the trees and wildlife within were venerated and given total protection. Examples- Khasi and Jaintia Hills in Meghalaya, Aravalli Hills of Rajasthan.
Fig. Khasi Hills
- In ex-situ conservation, threatened animals and plants are taken out from their natural habitat and placed in special setting where they can be protected and given special care. Examples- Zoological parks, botanical gardens and wildlife safari park.
- Gametes of threatened species can be preserved in viable and fertile condition for long periods using cryopreservation techniques, eggs can be fertilized in vitro, and plants can be propagated using tissue culture methods.
