In the Ecology and Conservation Biology category

The Frontiers of Knowledge Award goes to Gerardo Ceballos and Rodolfo Dirzo for quantifying the scale of the Sixth Mass Extinction of species

The BBVA Foundation Frontiers of Knowledge Award in Ecology and Conservation Biology has gone in this sixteenth edition to two Mexican scientists who have documented and quantified the scale of the Sixth Mass Extinction, that is, the widespread loss of biodiversity brought about by human activity. Gerardo Ceballos (National Autonomous University of Mexico, UNAM) and Rodolfo Dirzo (Stanford University) are hailed by the committee as “trailblazing researchers in ecological science and conservation,” whose joint work in Latin America and Africa “has established that current species extinction rates in many groups of organisms are much higher than throughout the preceding two million years.” In effect, by documenting losses of animals and plants in some of the Earth’s most biodiverse habitats, both have contributed to showing that today’s biodiversity crisis is, as the citation states, “an especially rapid period of species loss occurring globally and across all groups of organisms, and the first to be tied directly to the impacts of a single species, namely, us.”

31 January, 2024

The two awardee ecologists have catalyzed the global study of “defaunation,” a term Dirzo coined to describe the alterations causing the disappearance of animals in the structure and function of ecosystems. His research, says the citation, has revealed how the elimination of a single species can trigger pernicious “cascading effects” by disrupting the web of interactions it maintains with other organisms. This, in turn, has adverse effects on human wellbeing through the reduction of the goods and services they perform. His work has helped provide the “necessary scientific basis” to further the adoption of evidence-led conservation measures.

“The experimental work done by professors Ceballos and Dirzo has led the way in quantifying the extent of species loss,” explains Pedro Jordano, a Research Professor in the Department of Integrative Ecology at Doñana Biological Station (CSIC) and secretary of the award committee. “And what is truly shocking about their results is that this species extinction rate, or ‘defaunation process’, as it is known, is advancing today at a speed several orders of magnitude above the rate recorded over the last two million years. This shows that we are up against a truly intimidating challenge; one that these two researchers have documented and assessed across thousands of vertebrate, invertebrate and plant species.”

Another committee member, Miguel Bastos Araújo, Research Professor in the Department of Biogeography and Global Change at the National Museum of Natural Sciences (CSIC) in Madrid, uses an analogy to highlight the importance of the awardees’ work: “Imagine we are flying in a plane sitting next to the window. And looking out, we see bits of the plane falling off. It may not nosedive straight away, but the first thought that crosses the passenger’s mind is: how long can this plane keep flying without its component parts? Something similar occurs with ecosystems. As they lose their “parts” or species, they also lose vital functions, and it is these functions that provide essential services. The work of Dirzo and Ceballos is a valuable addition to the understanding of how such losses affect the resilience and sustainability of our ecosystems, shedding light on the urgent need for conservation actions to preserve the integrity of these systems that are critical to our survival.”

An accelerating extinction rate driven by our own species

Ceballos and Dirzo’s endeavors have advanced in tandem through most of their professional careers, with results in many cases complementing one another’s. But the origin of their collaboration lies back in the early 1980s, when both were studying at the University of Wales (United Kingdom), Dirzo pursuing his doctorate courses and Ceballos completing his master’s degree. They first connected over their shared concern at the increasingly evident impact on nature of human activity. “We started having conversations not just on scientific matters, but about how worried we were about the anthropogenic impact on the natural world we were seeing all around us,” Dirzo recalls.

Further ahead, Ceballos turned his research attention to the study of wildlife and the magnitude of the advancing extinction, while Dirzo centered his efforts on ecological interactions between plants and animals, and the consequences of this extinction.

Ceballos’ work on assessing current rates of extinction led him to explore comparisons with the rates of the past. “Evolution operates as a process of species extinction and generation,” he relates. In normal periods, more species appear than disappear, such that diversity gradually expands. There have been five mass extinction events in the last 600 million years, the last of which brought the demise of the dinosaurs. All had in common that they were catastrophic – wiping out 70% or more of the world’s species – had their origins in natural disasters, like a meteorite collision, and were extremely rapid in geological terms, lasting hundreds of thousands or millions of years.”

After a detailed analysis of numerous species, a research team led by Ceballos concluded – in a paper published in Science Advances in 2015 – that vertebrate extinction rates are from 100 to 1,000 times greater than those prevailing over the last few million years. “What this means is that the vertebrate species that have died out in the past 100 years should have taken 10,000 years to become extinct. That is the magnitude of the extinction,” he explains. His work pointed one way only; to the fact that the sixth mass extinction was already upon us, a scenario that for Ceballos has three major implications: “The first is that we are losing all that biological history. The second is that we are losing living creatures that have accompanied us through time and have been key in driving forward human evolution. And the third is that all these species are assembled in ecosystems that provide us with the environmental services that support life on Earth, like the right combination of gases in the atmosphere, drinking water, fertilization… Without these environmental services civilization as we know it cannot be sustained.”

The grave impact of extinction on ecosystem services

Species extinction is the last stage in the process, but Ceballos insists that population extinction is no less worrying, since it is these populations that provide environmental services on a local or regional scale. He gives an example: “It doesn’t matter if there are jaguars in Brazil if they have died out in Mexico, because the environmental services they performed in Mexico will have disappeared with them.”

Ceballos and his colleagues explored this concept in a study of prairie dog populations, which in the 1990s were thought to be pests and were the target of eradication campaigns. Through this study, published in 1999 in the Journal of Arid Environments, they were able to prove that, rather than pests, they actually play a vital role in maintaining their ecosystem, the grasslands of the southwest of the United States and north of Mexico.

“We found that prairie dogs were essential to the upkeep of ecosystem services, because if they are lost it sets off a chain of extinctions across the many other species who depend on them.” With these rodents gone, the soil becomes less fertile, erosion increases and the scrubland advances, wiping out the plants that serve as forage for livestock. “The impact on environmental services is colossal,” he affirms.

For the Mexican ecologist, the biodiversity crisis we are experiencing is of a magnitude similar to the crisis of climate change and both problems are closely interrelated: “We have to couple the issue of species extinction with the issue of climate change, and understand that it is a threat to humanity’s future.”

From deforestation to “defaunation”: the “cascading effect” of species loss

On his return from Wales, Rodolfo Dirzo, newly appointed to a post at UNAM, traveled to one of the university’s nature reserves in the state of Veracruz, hosting the world’s northernmost tropical rainforest. “I could see the consequences of human impacts all around the reserve,” he recalls: “And I was soon asking myself: these fascinating things I study, the ecology and evolution of plants and animals and their interactions, may not be around to study in future if we don’t start to do something about what is happening to natural systems.” This concern, which he shares with Ceballos, has guided Dirzo’s steps throughout his career, from Mexico to the United States.

That Veracruz reserve was home to a lush, intensely green forest, but Dirzo realized that it had barely any animal life, and that the leaves of the plants grew unrestricted with no organisms to feed on them. The scientist began studying the effects of this phenomenon and published his findings in a chapter of the book Plant-Animal Interactions: Evolutionary Ecology in Tropical and Temperate Regions in 1991.

By analogy with deforestation, he came up with the term “defaunation” to refer to the imbalance entailed by the absence of animals. “Everyone has a mental picture when they hear the word deforestation. They understand that what they are seeing is a problem, the erosion of ecosystems due to loss of vegetation. And it occurred to me that the word “defaunation” could be a way to highlight that, just as Earth’s ecosystems face a serious problem of deforestation, another serious threat lies in the depletion and possible extinction of animal species.”

“Species do not live in an ecological vacuum,” he points out, insisting that it is not just species disappearances we have to worry about, but the extinction of species populations and, above all, species interactions, which should accordingly be a core focus of conservation actions.

“Imagine that we eliminate the elephants, giraffes, zebras and buffalos from an African savannah, all the large vertebrates that define the savannah’s function. Without these animals, plants at ground level will grow much more, soil compaction will lessen, fruits and seeds will fall from the trees without being eaten, and will pile up on the ground instead of having animals disperse them by ingestion and transport.”

Elephant poaching and the risk of pandemics

These effects, Dirzo explains, give rise to a phenomenon that he refers to as “winners and losers.” When these large animals die out locally, they are evidently losers, while smaller animals like rodents take advantage of their absence and therefore become winners. But these smaller animals also carry pathogens like Leptospira, Leishmania and even the bacteria that causes bubonic plague. So if populations of these pathogen-carrying animals increase, there is a greater chance that they will transmit diseases to humans. “We could be put at risk of suffering a new pandemic,” he affirms, “given the proliferation of these diseases and the current mobility of human beings.”

The researcher has verified these effects through experiments carried out in Africa. He and his team installed electrified fences in some very well-conserved parts of the savannah to stop large animals from entering. They then left other areas unfenced, so they could compare two identical ecosystems, one with large wildlife and one without. “We found that when an area is closed off to these animals, the savannah vegetation changes dramatically.” Further, the rodent population triples, as does the risk of diseases that can be transmitted to humans. In this way, he says, we get “a cascade that runs from elephant poaching to the real risk of a new human pandemic.”

In fact, it is not even necessary for a whole local population to die out for it to pose an ecological problem. If there are not enough individuals to maintain viable populations, the species in question can no longer interact with other organisms and fulfill its ecosystem function. It becomes what is known, says Dirzo, as a “living dead species.”

Hunting is just one human activity that can drive species populations totally or partially extinct and trigger such grave effects as a pandemic. Dirzo lists five key factors that drive defaunation: land use change for pasture or urban development; the overexploitation of resources; pollution – by anything from noxious chemical products to marine plastic waste; the introduction of non-native or invasive species in ecosystems where they don’t belong; and climate change. “But none of these five factors,” he adds, “operates in isolation: they are all interlinked, and this makes the challenge of dealing with biological extinction all the more complex.”


A total of 47 nominations were received in this edition. The awardee researchers were nominated by Gretchen Cara Daily, Bing Professor of Environmental Science at Stanford University (United States) and 2018 Frontiers of Knowledge Laureate in Ecology and Conservation Biology.

Ecology and Conservation Biology committee and evaluation support panel

The committee in this category was chaired by Emily Bernhardt, James B. Duke Distinguished Professor and Chair of the Department of Biology at Duke University (United States) The secretary was Pedro Jordano, Research Professor in the Department of Integrative Ecology at the Doñana Biological Station (EBD-CSIC) and Associate Professor in the Department of Plant Biology and Ecology at the University of Seville (Spain). Remaining members were Miguel Bastos Araújo, Research Professor in the Department of Biogeography and Global Change at the National Museum of Natural Sciences, CSIC (Spain); Paul Brakefield, Professor of Zoology and Emeritus Director of the Museum of Zoology at the University of Cambridge (United Kingdom); María Begoña García, Tenured Scientist in the Department of Biodiversity Conservation at the Pyrenean Institute of Ecology, IPE-CSIC (Spain); Rik Leemans, Professor in Environmental Systems Analysis at Wageningen University & Research (Netherlands); and Nuria Marbà, Research Professor in the Global Change Research Group at the Mediterranean Institute for Advanced Studies, UIB-CSIC (Spain).

The evaluation support panel was coordinated by Anna Traveset Vilaginés, Research Professor at the Mediterranean Institute for Advanced Studies (IMEDEA, CSIC-UIB), and formed by: Xavier Bellés Ros, Ad Honorem Associate Professor at the Institute of Evolutionary Biology (IBE, CSIC-UPF); Marta Coll Monton, Scientific Researcher at the Institute of Marine Sciences (ICM-CSIC); and Marío Díaz Esteban, Research Professor at the National Museum of Natural Sciences (MNCN, CSIC).

About the BBVA Foundation Frontiers of Knowledge Awards

The BBVA Foundation centers its activity on the promotion of world-class scientific research and cultural creation, and the recognition of talent.

The BBVA Foundation Frontiers of Knowledge Awards, funded with 400,000 euros in each of their eight categories, recognize and reward contributions of singular impact in physics and chemistry, mathematics, biology and biomedicine, technology, environmental sciences (climate change, ecology and conservation biology), economics, social sciences, the humanities and music, privileging those that significantly enlarge the stock of knowledge in a discipline, open up new fields, or build bridges between disciplinary areas. The goal of the awards, established in 2008, is to celebrate and promote the value of knowledge as a public good without frontiers, the best instrument to take on the great global challenges of our time and expand the worldviews of each individual. Their eight categories address the knowledge map of the 21st century, from basic knowledge to fields devoted to understanding and interrelating the natural environment by way of closely connected domains such as biology and medicine or economics, information technologies, social sciences and the humanities, and the universal art of music.

The BBVA Foundation has been aided in the evaluation of nominees for the Frontiers Award in Climate Change by the Spanish National Research Council (CSIC), the country’s premier public research organization. CSIC appoints evaluation support panels made up of leading experts in the corresponding knowledge area, who are charged with undertaking an initial assessment of the candidates proposed by numerous institutions across the world, and drawing up a reasoned shortlist for the consideration of the award committees. CSIC is also responsible for designating each committee’s chair across the eight prize categories and participates in the selection of remaining members, helping to ensure objectivity in the recognition of innovation and scientific excellence.