Importance of species diversity to the ecosystem

It is worth asking whether all this diversity really matters -- what would happen if a few species were permanently lost? A community is generally considered stable if its average biomass production stays fairly constant over time, if it can withstand and quickly recover from disturbances, and if it resists being overrun by invasive species. Through a series of field experiments, the ecologist David Tilman showed that greater species richness does help stabilise an ecological community -- richer diversity is associated with less fluctuation in biomass production over time, an idea now known as the Productivity-Stability Hypothesis.

The Stanford ecologist Paul Ehrlich offered a memorable analogy for why diversity matters, called the Rivet Popper Hypothesis. He compared an ecosystem to an aeroplane held together by thousands of rivets, with each species acting as one rivet. If passengers begin popping out rivets one at a time -- that is, if species are lost from the ecosystem one by one -- the plane may show little sign of trouble at first. But as more and more rivets are removed, the structure becomes progressively weaker until it poses a serious safety risk. Crucially, which rivets are removed matters just as much as how many: losing rivets that hold the wings to the body (that is, losing key or keystone species) causes far more immediate danger than losing less critical ones. In short, the relationship …