The importance of Species Diversity to the  Ecosystem

By Siddharth Sanghvi

Does the number of species in a community really matter to the functioning of the ecosystem?

For many decades, ecologists believed that communities with more species, generally, tend to be more stable than those with less species. 

For many decades, ecologists believed that communities with more species, generally, tend to be more stable than those with less species. 

 What exactly is stability for biological community?  A stable community  1. Should not show too much variation in productivity from year to year; 

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 What exactly is stability for biological community?  A stable community  2. it must be either resistant or resilient to occasional disturbances (natural or man-made)

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 What exactly is stability for biological community?  A stable community  3.  it must also be resistant to invasions by alien species.

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NCERT don’t know how these attributes are linked to species richness in a community ?

David Tilman’s long-term ecosystem experiments using outdoor plots provide some tentative answers.

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Tilman believed biodiversity was a major factor to improve land productivity. He decided to prove it by conducting experiments at an actual farm.

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It was the world's first large-scale experiment, in which the influence of biodiversity on productivity was investigated.

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– 1) In one corner of a field station, many 9-meter-square plots were prepared. – (2) Each plot was planted with either 1, 2, 4, 8 or 16 different prairie perennial species, all randomly chosen; their growth per unit area was observed for over 20 years.

Tilman's experiment has shown that biodiversity is of central importance to the productivity, stability, resistance to invasion of ecosystems, and to the fertility of their soils. 

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For example, plots seeded with 16 different species were 200% more productive than these same species grown in monoculture plots.  It was a discovery that overturned the conventional wisdom of ecology.

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Tilman found that plots with more species showed less year-to-year variation in total biomass. He also showed that in his experiments, increased diversity contributed to higher productivity

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Although, NCERT may not understand completely how species richness contributes to the well-being of an ecosystem ..........

we know enough to realise that rich biodiversity is not only essential for ecosystem health but imperative for the very survival of the human race on this planet.

How ?

Biodiversity is essential for ecosystem health ?

First is  mechanism comes from the ability of competing species to replace or compensate for one another and thus minimize, at higher diversity, the ups and downs in functioning.

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Another mechanism is the . portfolio effect,. a theory which suggests that cumulative properties such as ecosystem functioning show less severe fluctuations in systems with many species,

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...... much the way investment portfolios of varied stocks have lower long term variance than portfolios of one or a few kinds of stocks

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Complementarity effect : This occurs when increasing diversity results in increasing numbers of species that are complementary .....

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rather than competitive in the use of resources, exploiting different niches, such as rooting depths, and allowing more effective use of available resources

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Does it really matter to us if a few species become extinct?

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Keystone species are those species whose importance to an ecosystem’s structure, composition, and function is disproportionately large relative to their abundance.

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These species can be of any life form, but they have in common an eff ect on their environment that is always greater than what can be expected based on their biomass . Well-studied examples include sea stars, beavers, bears, corals, elephants, and hummingbirds.

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Stanford ecologist Paul Ehrlich's

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In an 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 (proper functioning of the ecosystem) initially.....

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but as more and more rivets are removed, the plane becomes dangerously weak over a period of time. Furthermore, which rivet is removed may also be critical. 

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 Loss of rivets on the wings (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.

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