Tilman (Illinois, United States, 1949) has provided a firm scientific foundation for the need to conserve our planet’s biodiversity. His paradigm-challenging findings were written up in one of the most cited papers in modern ecology, published in Nature in 1994.

Looking back at that time, he recalls: “It was a real surprise, because until then everyone thought that ecosystem functioning was controlled by a few dominant species, and the rest didn’t matter. Ecosystems should be conserved, certainly, but for moral rather than scientific reasons. Our discovery that less diverse systems were also less stable sparked a major discussion, with many saying that our work must be flawed.” It was then that he set up “the world’s first biodiversity experiment in the field,” because “there was simply no data available to resolve the debate.”

“Surprised and totally delighted,” Tilman described his feelings on hearing of the award, before launching into an impassioned defense of the value of biodiversity: “It is incredibly important. We have to understand this because we are living in a time when humans are taking high-diversity natural systems and making them very simple, with very low diversity. Our work has shown that this severe decline has significant long-term impacts on the quality of these ecosystems and how they function, which mean they can no longer provide us with the services we want from them, such as clean water or the storage of carbon.”

Tilman’s research and teaching career has unfolded at the University of Minnesota, which he joined in 1976, rising 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.

The new laureate has also described the mechanisms of biodiversity maintenance. The jury, specifically, singles out his efforts to unravel one of the oldest mysteries in ecological science, dating from the times of Charles Darwin: How can so many species coexist within a single ecosystem? To find the answer, Tilman factored into his theoretical models the idea that each species specializes in what it does best at the expense of other possible uses of its energy, and concluded that it is this trade-off (between, for instance, greater competitive vs. dispersal ability) that permits the coexistence of multiple species.

He takes time to explain the links between biodiversity and his findings in this area: “These trade-offs are the central reason why biodiversity matters, because the ecosystem operates as a network of abilities, and the greater the variety of abilities, the better it works.” And goes on to draw a parallel with human society, where we have people who are journalists, teachers and so on. People doing what they do best is what makes society function.

The jury also highlights the “significant implications” of Tilman’s work “in the realm of conservation and global land use” as well as in practical issues of immediate concern. One such issue is the production of biofuels, which he has shown can only be environmentally advantageous if it is biodiversity enhancing and makes use of species not for human consumption. The jury’s citation expands on this point: “He has shown that mixtures of native perennial grasses provide more net energy per acre than corn grain ethanol.” Traditional biofuels, as such, would generate far higher carbon emissions than the carbon storage they would supposedly provide.

“Biofuels are not the solution to our problem of greenhouse gas emissions,” Tilman contends. To start with, “there are very few ways to make a biofuel that is environmentally beneficial,” and those that exist involve growing plants not used for human consumption with techniques that foster biodiversity. Even so, “biofuels can only replace around 10% of our diesel and gasoline use, so they will never be a solution to the whole emissions problem. It matters much more to develop efficient forms of transport.”

Finally, the jury refers to Tilman’s finding that the relationship between the degree of ecosystem destruction and the impact on the species it harbors is more complex than might first appear, to the extent that we can talk about what he refers to as an “extinction debt”, whereby “the effects of habitat destruction on species extinctions may occur generations after the disturbance.”

Tilman is content nonetheless to call himself an optimist: “Because we have so many humans consuming so many resources, we are having impacts that the Earth has never seen before. But if you look back across human history, we have had many, many problems that we have been able to find solutions to, even if we don’t find them until the problems get serious. On the environment, we know how to solve the problems, what we haven’t done is implement the solutions.”

He is currently working on ways to boost agricultural productivity without simultaneously increasing its environmental impact: “The world uses about five billion hectares of land for agriculture. We have massive amounts of land in the poor nations of the world devoted to agriculture that has very poor yields. But if this land were managed better it could fully meet the population’s food needs now and in the future, in an environmentally friendly way. What we need to do is go there and teach people to farm more efficiently. If we did that, there would be no pressure on them to clear more land for food production.”

In one of his latest papers, published in Nature in November 2014, Tilman explores ways to feed the world while saving the Earth’s biodiversity that are conducive to both lower greenhouse gas emissions and improved human health.

Ecology and Conservation Biology jury

The jury in this category was chaired by Georgina Mace, Professor of Biodiversity and Ecosystems at University College London (United Kingdom), with Jordi Bascompte, Professor of Ecology in the Institute of Evolutionary Biology and Environmental Studies at the University of Zurich (Switzerland) acting as secretary. Remaining members were Gerardo Ceballos, professor in the Instituto de Ecología of the Universidad Nacional Autónoma de México (Mexico), Pedro Jordano, Research Professor in the Department of Integrative Ecology of the Estación Biológica de Doñana (CSIC) (Spain), and Hanna Kokko, Professor of Evolutionary Ecology at the University of Zurich (Switzerland).