As I noted in the last two posts, evolutionary biology shows us that species evolve in non-deterministic, non-hierarchical way and the Gaia Hypothesis (now accepted as a proven theory for the “weak” statement of it) maintains that they collectively contribute to the maintenance of conditions of Earth's surface within a range conducive to the persistence and perpetuation of life. But how do individual species contribute to the web of life on Earth and weather and how biodiversity matter? Since 1990s, these questions have been tackled by ecologists who have shown that while contribution of species to the maintenance and flourishing of ecosystems vary in degrees, they each contribute to it is a meaningful way and biodiversity is essential for continuation of life on Earth.
“Because every species influence Earth’s chemistry—sometimes in barely detectable ways, sometimes in major ways—every species can be said to have a function (though not in the sense of purpose). … [T]he best way to deduce what function a part plays in an ecosystem is to remove it and see what happens. This is standard practice in ecology, with the University of Washington zoologist Robert Paine’s experiment in the 1960s being perhaps the best-known example.
“Paine removed a single species of starfish (Pisaster ochracues) from an intertidal community in Mukkaw Bay, Wash., and found that its absence allowed a prolific species of mussel (Mytilus californianus) to grow and displace most of the other species in the ecosystem. The starfish functioned as a regulator of mussel density, something that could only make sense in the context of the intact ecosystem.”[ii]
Naeem explains that Paine’s method does not result in an explanation of biogeochemistry function of the starfish. To do that one must measure how the distribution of elements in Mukkaw Bay changes in the presence or absence of the starfish. And this is a difficult task; it requires removal of all starfish, and keeping them out for a long time to detect the resulting biogeochemical changes. Alternatively, one can count up all the starfish in the region, determine the respiration rate and estimate how much carbon dioxide they release into the water and atmosphere in a given year. One can also estimate how much carbon they consumed and how much they excreted as waste, and do the same for nitrogen, oxygen, sulfur, phosphorus, and so on, until all the likely influences of the starfish species on the ecosystem’s geochemistry were determined.
“As this exercise shows, to determine the functional significance, in terms of biogeochemistry, of even a single species is a daunting task. For this reason, there are few species whose biogeochemical impact are experimentally known. In most cases, as we did for starfish, one estimates what their function is based on size, abundance, growth rates and other biological properties.”[iii]
In the 1990s, ecologists began to reverse engineer ecosystems. A pioneering reverse engineering experiment was the study conducted at Imperial College of London’s Centre for Population Biology under Sir John Lawton, by several scientists including Naeem, of a weedy meadow typical of Berkshire County, England.
“…[W]e deliberately engineered our ecosystem to be different from a real ecosystem in one specific detail: All our meadows were identical except for the amount of biodiversity each had. Six of the chambers contained ecosystems with 31 species of plants and animals inside; four contained only 16 of the original 31 species; another four chambers had just 10. Everything else was the same—the same volume of soil, same amount of light, same amount of water added each day, same breeze, same timing of dusk and dawn.
“What we found was quite surprising. The amount of carbon dioxide absorbed by the communities, the amount of biomass they produced, the fertility of the soil and the amount of water retained by the ecosystems differed. Because everything was held constant among the ecosystems except for their biodiversity, the only conclusion we could come to was that our monkeying with the number of species was sufficient to drastically change the way ecosystem functioned. Most important, there was a clear pattern that related how many species were in the ecosystem with how much carbon dioxide it absorbed: More diversity led to greater absorption of carbon dioxide.
“… There was no doubt that ecosystems were critical to the processes such as the cycling of carbon dioxide between the atmosphere and biosphere and the cycling of nutrients between soil, water and the atmosphere, and that these processes were an integral part of global environmental process. The Weak Gaia Hypothesis already told us this. There was also no doubt that some species had strong impacts on an ecosystem while others—such as Paine’s starfish in Mukkow Bay—had weak impact. But no one had experimentally tested the idea that simply reducing the number of species would change ecosystem function.
“Since then there have been numerous studies that have been variations on the same theme—hold as many factors constant as possible, vary biodiversity, then see what happens to the functioning of the ecosystem. …
“These experiments found that some species, when left out, had no detectable effect on biogeochemistry, while in others, if left out, had dramatic effects. But, on average, the removal of species caused changes in ecosystem functioning, and the more species one removed, on average, the stronger these changes become.”[iv]
There are many reasons why loss of biodiversity affects ecosystems. Naeem notes two that emerge most often in experimental research.
“First, the more species one removes, the greater the probability that an extraordinary important species will be lost. But there is a second reason that biodiversity loss reduces ecosystem function: complementarity. The more species you have, the more ways they make use of limited resources such as light, water, nutrients and space.”
The United Nations commissioned Millennium Ecosystem Assessment, a five-year effort to assess the state of the planet, published in 2005 and 2006, has become the standard reference for the state of the biosphere.
“This Assessment places biodiversity squarely at the center of all the environmental processes that affect human wellbeing. Whether the environmental problem is the spread of emerging diseases, control of invasive species, food security or climate regulation, and whether we are talking about human health, poverty, education or even freedom itself, almost all aspects of human well-being and prosperity traces back to biodiversity for their foundation.”[v]
While there is a bit of instrumentalist view of nature in Naeem’s concluding paragraph, it offers much wisdom backed by scientific research on how each individual species contributes to the functioning and prosperity of the web of life on Earth and that biodiversity much like cultural diversity enriches it. Here is further evidence for the ethical foundations of Deep Ecology as well why any sound theory of radical social change needs to be based on ecocenterism.