Biology IMPORTANCE OF SPECIES DIVERSITY

### KEY TOPICS

star Criteria for stability for a biological community
star The importance of Species Diversity to the Ecosystem
star Loss of Biodiversity

### CRITERIA FOR STABILITY FOR A BIOLOGICAL COMMUNITY

● Does the number of species in a color{violet}("community really matter") to the functioning of the color{violet}("ecosystem?") This is a question for which ecologists have not been able to give a definitive answer.

● For many color{violet}("decades, ecologists") believed that color{violet}("communities") with more species, generally, tend to be more stable than those with less species.

● There are some criteria that color{violet}("confer stability") to a color{violet}("biological community :")

star A color{violet}("stable community") should not show too much color{violet}("variation in productivity ") from year to year

star It must be either color{violet}("resistant or resilient") to color{violet}("occasional disturbances (natural or man-made)")

star It must also be color{violet}("resistant to invasions") by alien species.

### THE IMPORTANCE OF SPECIES DIVERSITY TO THE ECOSYSTEM

● We don’t know how these attributes are linked to species richness in a color{violet}("community"), but color{brown}("David Tilman’s") long-term ecosystem experiments using outdoor plots provide some tentative answers.

● color{violet}("Tilman") found that plots with more species showed less color{violet}("year-to-year variation") in color{violet}("total biomass.")

● He also showed that in his experiments, color{violet}("increased diversity contributed") to higher productivity.

● Although, we may not understand completely how species color{violet}("richness contributes") to the well-being of an color{violet}("ecosystem,") we know enough to realize that color{violet}("rich biodiversity") is not only essential for color{violet}("ecosystem health") but imperative for the very survival of the human race on this color{violet}("planet.")

● At a time when we are losing species at an alarming pace, one might ask–

star Does it color{violet}("really matter") to us if a few species become extinct?

star Would color{violet}("Western Ghats ecosystems") be less functional if one of its tree frog species is lost forever?

star How is our quality of color{violet}("life affected") if, say, instead of color{violet}("20,000 ") we have only color{violet}("15,000") species of ants on earth?

● There are no direct answers to such näive questions but we can develop a proper perspective through an analogy the (color{brown}(" ‘rivet popper hypothesis’") ) used by Stanford ecologist color{brown}("Paul Ehrlich.")

● In an color{violet}("airplane (ecosystem)") all parts are joined together using thousands of rivets (species).

● If every passenger travelling in it starts popping a rivet to take home (causing a species to become extinct), it may not affect flight safety (color{violet}("proper functioning of the ecosystem")) initially, but as more and more rivets are removed, the plane becomes dangerously weak over a period of time.

● Furthermore, which color{violet}("rivet is removed") may also be critical.

● Loss of rivets on the wings (color{violet}("key species that drive major ecosystem") functions) is obviously a more
serious threat to flight safety than loss of a few rivets on the seats or windows inside the plane.

### LOSS OF BIODIVERSITY

● While it is doubtful if any new species are being added (through speciation) into the color{violet}("earth’s treasury ")of species, there is no doubt about their color{violet}("continuing losses.")

● The color{violet}("biological wealth") of our planet has been declining rapidly and the accusing finger is clearly pointing to human activities.

● The colonisation of color{violet}("tropical Pacific Islands") by humans is said to have led to the extinction of more than 2,000 species of color{violet}("native birds.")

● The color{brown}("IUCN Red List (2004)") documents the extinction of 784 species (color{violet}("including 338 vertebrates, 359 invertebrates and 87 plants")) in the last 500 years.

● Some examples of recent extinctions include the color{violet}("dodo") (Mauritius), color{violet}("quagga") (Africa), color{violet}("thylacine") (Australia), color{violet}("Steller’s Sea Cow") (Russia) and three subspecies (Bali, Javan, Caspian) of tiger.

● The last twenty years alone have witnessed the disappearance of 27 species.

● Careful analysis of records shows that color{violet}("extinctions across taxa") are not random; some groups like amphibians appear to be more vulnerable to extinction.

● Adding to the grim scenario of extinctions is the fact that more than 15,500 species world-wide are facing the threat of extinction.

● Presently, color{violet}("12 per cent") of all bird species, color{violet}("23 per cent") of all mammal species, color{violet}("32 per cent") of all amphibian species and color{violet}("31per cent") of all color{violet}("gymnosperm") species in the world face the threat of extinction.