Biodiversity & Environmental Issues Test - 10

Among all the species in the world, approximately 70% are animals and 22% are plants. In animals, insects account for 70% -80%, which is the maximum (represented as A). According to, IUCN (2009) there are 10,25,000 species of insects and 70,000 species of molluscs (represented as B).

Excessive exploitation of a species, whether a plant or animal reduces size of its population such that it becomes vulnerable to extinction. Dodo, passenger pigeon and Steller 's sea cow become extinct in the last 500 years due to  over-exploitation by humans.

Barring arid/semi-arid and aquatic habitat, biodiversite shows a latitudinal and altitudinal gradients. There is little biodiversity at the poles. It increases in temperate areas but reaches the maximum in tropical rain forests at equator. It is because the tropical rain forests have favorable environmental conditions not only for speciation but also for supporting both variety and number of organisms.

The relationship between species richness and area is rectangular hyperbola for a wide variety of taxa whether they are birds, bats, freshwater fishes or flowering plants and the equation can be given as S = CA^Z . On a logarithmic scale it is straight line described by the equation logS = logC + ZlogA. Where S is species richness, Z is slope of line or regression coefficient, C is Y-intercept while A is area.

The world is facing acceleration rates of species extinctions, largely due to human interference. There are four major causes collectively called as the evil quarter, it includes (i) Habitat loss and fragmentation, (ii) Oven exploitation, (iii) Alien species invasions and (iv) Co-extinctions.

Lantana, Eichhornia and African catfish. are exotic species. Non-native or exotic species are often uses. They introduced inadvertently for their economic and other uses. They often becomes invasive and drive away the local species. These species are considered to be second major cause of extinction of species are considered to be second major cause of extinction of species. Such invasive exotic species have proved harmful to both aquatic and terrestrial ecosystems.

Lantana, Eichhornia and Parthenium are all exotic species, which had been introduced in India. Lantana camara has replaced many species in forests of Uttar Pradesh and Madhya Pradesh. Eichhornia (Water hyacinth) has clogged water bodies including wetlands resulting in death of servral aquatic plants and animals. Parthenium has pushed out several herbs and shrubs from open places in the plains.

Among vertebrates, fish account for the maximum share with approximately 26,959 species. Birds have 9,700 identified species and reptiles have 7,150 species.

There are  2,70,000 species of higher plants and  72,000 species of fungi  and in the world.

Nile Perch (a predator fish) was introduced in lake Victoria of East Africa. It killed and eliminated ecoligically unique assemblage of over 200 native species of small cichild fish.