David Tilman (Illinois, United States; 1949) earned a BSc in Zoology in 1971 and a PhD in Ecology in 1976, both at the University of Michigan. His academic career has since unfolded at the University of Minnesota, where he rose to a professorship in 1984. Since 1992, he has headed the University’s Cedar Creek Ecosystem Science Reserve, a 5,400-acre research station where he set up the experimental systems for long-term study that led him to his fundamental contributions.
Tilman has published over 260 papers in high-impact journals. In the periods 1991-2000 and 2001-2010 he was deemed the most cited ecologist and environmental scientist by Essential Science Indicators. Founding Editor of Issues in Ecology, he has served on the editorial boards of Science and Proceedings of the National Academy of Sciences, among other publications.
David Tilman is a member of the U.S. National Academy of Sciences and the American Academy of Arts and Sciences. His many distinctions include the Robert H. MacArthur Award of the Ecological Society of America, the International Prize for Biology (Japan) and the Alexander von Humboldt Medal.
Speech
Ecology and Conservation Biology 7th edition
“Probably the most amazing feature of Earth is the existence of life. And the most amazing feature of life is the phenomenal number of species.”
“Probably the most amazing feature of Earth is the existence of life. And the most amazing feature of life is the phenomenal number of species.”
TUITEAR
David Tilman, the author of this observation, became an ecologist in order to understand the origin of life’s variety. And the question led him to a startling revelation: that ecosystem health depends precisely on the biodiversity that so enthralled him. It is for this insight that Tilman has been granted the latest BBVA Foundation Frontiers of Knowledge Award in Ecology and Conservation Biology.
His research — in the words of the jury — “quantified for the first time the value of preserving biodiversity by unequivocally showing that more diverse communities are more productive, more resilient to invasions, and more stable in the face of perturbations such as drought.”
The news of his discovery would land Tilman, a professor at the University of Minnesota, in the thick of a controversy. It was indeed, he acknowledges, “a considerable upset,” because the science of the time said exactly the opposite: the more species an ecosystem harbored the less sustainable it would be.
“Everyone thought that ecosystem functioning was controlled by a few dominant species, and the rest didn’t matter. That ecosystems should be conserved, certainly, but for moral rather than scientific reasons. So our discovery sparked a major discussion, with many saying the work must be flawed,” he recalls. No surprise then that the resulting paper, published in Nature in 1994, is one of the most widely cited in modern ecology. “When a 20-year paradigm is challenged, it leads to a host of new questions.”
Tilman was not driven by any conscious desire to overturn the established wisdom. A lover of mathematics and also of nature, for him ecology represented the union of these two passions: if the natural environment consists of multiple interplaying elements, surely mathematics can be the powerful magnifying glass that reveals its underlying laws. So from the time of his PhD research on how Lake Michigan algae compete for resources, Tilman has studied ecosystem functioning through an ongoing dialogue between theory and experimentation.
It was with experiments set up in the early 1980s in the fields of Cedar Creek, Minnesota, that he obtained his polemical result. He traces it back to two chance events: a period of drought in 1988 and a congress he attended in Germany, where the question was raised of whether biodiversity could affect ecosystem functioning. “That led me to wonder what the impact of the drought had been,” he says. And on analyzing the data, “we found strong support for the hypothesis that more diversity equaled more stability.” His response to the ensuing debate was to launch the first long-term field experiment to study biodiversity, which continues to this day.
However this new result begged a further question: Why do ecosystems benefit from more variety? To find the answer, Tilman factored into his theoretical models the idea that each species specializes in a particular skill at the expense of other uses of its energy — prizing success in dispersal, for instance, over competing for resources — and concluded that it was this tradeoff that held the key. Just as in human society different people perform different jobs, “the ecosystem operates as a network of abilities,” he explains, “and the wider the spectrum of abilities, the better it works.” Hence the importance of biodiversity.
These findings have major practical implications. In deciding biofuel policies, for example. Tilman has shown that biofuels are only environmentally advantageous if the species used come from wild grasslands; and the more biodiverse — and therefore productive — the better. By contrast, traditional biofuels derived from corn or sugar cane release more carbon to the atmosphere than they store, because their cultivation involves CO2 emissions — the result, frequently, of the previous clearing of forested land.
Also, mounting demand for biofuels drives up the price of human food crops, a situation Tilman condemns as ethically impermissible. “Biofuels are not the solution to our problem of greenhouse gas emissions,” he contends. “It matters much more to develop efficient forms of transport.”
He is currently working on ways to boost agricultural productivity without simultaneously increasing its environmental impact, the key being to improve crop yields in developing countries: “We know how to achieve more abundant harvests and to do so sustainably,” he explains. And if we can transmit this knowledge to the right people, “there will be no pressure on them to clear more land for food production.”
A recent set of findings weds nutritional and environmental considerations: the healthiest diets, Tilman assures, are also the best at preserving nature. Which are they? The vegetarian and — surprise — the Mediterranean. The point is worth noting, because “we live in a time when human beings are destroying habitats, simplifying ecosystems and driving species to extinction,” Tilman warns. And the risk is that these systems will stop supplying the services we depend on, like clean water or the storage of carbon. That’s why biodiversity matters.”
