Ernst Haeckel coined the term Ecology in the late 1800s. He derived the name from the Greek for house (οἶκος), but it was not the first time a holistic approach had been taken to the study of communities in situ. That distinction goes to Ancient Greek philosophers such as Hippocrates and Aristotle who studied Natural History.
The science of Ecology flourished in the 20th century but now it languishes in the shadows of biomolecular sciences like an old retired uncle in the corner.
And yet, one of its most powerful theories is as relevant today as it ever was.
The theory proposed that the more diverse a biotic community, the more stable it would be.
This is an idea that is intuitively appealing and it can be related to all sorts of situations from investment banking to the sociology of suburban life.
However, has the theory been tested and how does it perform under empirical scrutiny?
Let's take a look at the data from a couple of theoretical ecosystems.
Ecosystem One: Is this Diversity?
Ecosystem Two: Is this Diversity?
It's fairly obvious that Ecosystem Two is more diverse than Ecosystem One. One has only 10 species (this is called 'Species Richness') and a lower abundance in general, while the other has a Species Richness of 20 with some higher abundances.
However, what about Ecosystem Three below?
In fact, most ecologists take two factors into account when measuring the diversity of an ecosystem: Species Richness and something called Evenness, which is the abundance of species across the board. In that way they come up with something called a Diversity Index.
So, Ecosystem Three is the most diverse of the three.
However, this whole concept is in conflict with the idea of keystone species which may be low in abundance but pivotal in the functioning of the whole system. This is where Species Richness may indeed play an important role in the Stability of the ecosystem.
Both the early ecologist, Odum and Elton (1950 - 1970), concluded from their research that greatly simplified terrestrial communities often display more violent fluctuations in population density than diverse terrestrial communities. Furthermore, complex communities, constructed from many predators and parasites, prevented populations from undergoing explosive growth.
In 1982, Tilman began a long-term experimental study to investigate the relationship between diversity and stability in plant communities. His results support the hypothesis that diversity within an ecosystem tends to be correlated positively with plant community stability. However, field tests at the scale of the food web are few in number and very logistically difficult and expensive.
This caused experimental ecologists to turn to using controlled microcosms (often referred to as bottle experiments). None of these has proved to be convincing or definitive because of problems of scale. An exception may be the Ecotron at Imperial College which is a series of large, closed systems used for testing ecological theory.
Despite all experimental attempts to investigate the relationship between ecosystem Diversity and Stability, it has begun to dawn on modern ecologists that it is not the Diversity per se but the interactions between species (food webs, symbionts etc.) that confers the stability. And, furthermore, the many weak interactions may provide a surprisingly strong scaffolding.
So, based on sound ecological theory and emerging experiments, it seems that simply counting species is not enough to gauge ecosystem stability. What it takes is a deep understanding of the interactions between species.
And that is not simply a knowledge of interactions between the numerically dominant species, but even between the rare species and all others in the system. Furthermore, it is not enough to know only about the strong interactions, but the obscure weak ones as well.
Sadly, at the rate ecological research is being funded in Australia, there is little hope of investigating most food webs well enough to understand the long term impacts of species loss (even rare ones) on ecosystem stability.
Protecting vulnerable species is clearly not a legal game; it's a matter of the utmost importance. Current rapidly rising extinction rates, many undocumented, may be the herald of collapsing ecosystems. All the money in the world would not be sufficient to buy them back!