Species area relationship :-

• German naturalist and geographer Alexander von Humboldt observed that within a region species richness increased with increasing explored area, but only up to a limit.
• The relation between species richness and area for a wide variety of taxa such as angiosperm plants, birds, bats, freshwater fishes turns out to be a rectangular hyperbola.
• On a logarithmic scale, the relationship is a straight line described by the equation

log S = log C Log A
Where S= Species richness
A= Area
Z= slope of the line ssion coefficient)
C=Y-intercept.

• The species-area relationships among very large areas like the entire continents, the slope of the line is much steeper values in the range of 0.6 to 1.2)

Importance of species diversity to the ecosystem :-

Ecologists believe that communities with more species tend to be more stable than those with less species. This was confirmed by David tilman.

Characteristics of a stable community :-

• Productivity should not vary too much form year to year.
• It should be resistance to occasional natural and man made disturbances.
• It should be resistance to invasions by alien species.

Importance of biodiversity for survival of species can be explained by the ‘Rivet popper hypothesis’ proposed by paul ehrlich.

This hypothesis assumes the ecosystem to be an airplane and the species to be the rivets joining all parts together.

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 rivets are removed the plane becomes dangerously weal and fatal life of other species.

Loss of biodiversity :-

• It is caused by over population, urbanization and industrilisation.
• The colonization of tropical pacific islands by humans has led to the extinction of more than 2000 species of native birds.
• 15,500 species are facing the threat of extinction worldwide.
• At present, 31 percent of gymnosperms, 32 percent of amphibians, 12 percent of bird species and 23 percent of mammals face the threat of extinction.
• Some recently extinct species are dodo (Mauritius), quagga (Africa), thylacine (Australia ), stellar’s sea cow (Russia) and three tiger species (bali, jawan, Caspian).

Loss of biodiversity in a region may lead to :-

1. Decrease in plant production.
2. Less resistance to environmental disturbances such a drought.
3. Increased variability in ecosystem processes like plant productivity, water use, pest and disease cycles.