1. The introduction of Nile perch into Lake Victoria led to the extinction of more than 200 species of cichlid fish in that lake.
2. Introduction of African catfish Clarias qariepinus for aquaculture poses a threat to the indigenous catfishes in Indian rivers.
3. Carrot grass (Parthenium) and Lantana introduced into our country have become invasive and caused environmental damage; they pose a threat to the native species of plants in our forests.

1. Human beings obtain food, fibres, medicines and many industrial products from plants.
2. The wild relatives of our crops are useful as a source of disease-resistance, pest resistance and many desirable characters; they are used in breeding of plants to raise plants with desirable traits.
3. With increasing resources put into bioprospecting, exploring molecular, genetic and species leve1 diversity for economically important products, rich biodiversity will be beneficial.

The first Earth Summit was held in Rio de Janerio in 1992.
its objectives were:
(i) Conservation of biodiversity, and 
(ii) Sustainable utilisation of the benefits from biodiversity

India has high ecological diversity due to variety of topography, soil types, climates, rainfall zones, sea coasts.islands, etc. Ten well demarcated biogeographical zones with different biota occur in India.

Surface water, underground water, and sea water.

Stable community
(i) It shall not show too much variations in the year-to-year productivity.
(ii) It must be either resistant or resilient to sesonal disturbances.
(iii) It must be resistant to invasion of alien species.

Warm water can hold much less dissolved oxygen than cold water. Also, rise in temperature speeds up animal metabolism increasing O₂ requirement thus further aggravating O₂ problem for aquatic animals.

Carbon dioxide is a major greenhouse gas. Various human activities such as combustion of fossil fuels, electricity generation, transportation and industries are sources of its large scale production. Excess of CO₂ is harmful and considered as a pollutant. It is because it traps longer wavelength IR radiations reflected by earth's surface, thus causing global warming.

The human activities like deforestation, over-cultivation, unrestricted grazing, poor irrigation practices, result in arid patches of land (deforestation). When these large barren patches extend and remain unattended for long, a desert is created. Because the formation of fertile top layer of soil takes millions of years, desertification easily takes over.

Species-Area Relationship
1. Alexander Von Humboldt has observed that within a region, species richness increases with increased explored area, but only upto a limit.
2. The relationship between species richness and area for a number of taxa like angiospermic plants, freshwater fishes and birds is found to be a rectangular hyperbola.
3. On a log scale, the relationship becomes linear (straight line) and is described by the equation:
log S = log C + Z log A, where
S = Species Richness
Z = Slope of the line (regression coefficient)
A = Area and C = Y - intercept
4. Ecologists have found that the value of Z-line ranges between 0.1 and 0.2 irrespective of the taxonomic group of the region.
5. But in very large areas, like a continent, the Z value ranges between 0.6 and 1.2 and indicate species richness.

This is may be due to any following reasons:
(i) Fast growing species may compete with less vigorous local species.
(ii) Alien species will proliferate in that area if their natural pests and predators are not present.
(iii) by amensalism i.e. it may vigorously and may form conditions unfavorable for growth of local native species like Eichhornia.