Defaunation, like deforestation, threatens global biodiversity:
Interview with Rodolfo Dirzo, ecologist at Stanford University>
Rhett A. Butler, mongabay.com
May 20, 2008
Speaking in an interview with mongabay.com, Dr. Rodolfo Dirzo says that the disappearance of wildlife due to overexploitation, fragmentation, and habitat degradation is causing ecological changes in some of the world's most biodiverse tropical forests. He ranks defaunation — as he terms the ongoing biological impoverishment of forests — as one of the world's most significant global changes, on par with environmental changes like global warming, deforestation, and shifts in the nitrogen cycle.
"Climate change is very important and well-known form of change, but there are others, including land use change [and] fragmentation" he said. "Those environmental changes affect biodiversity quite significantly."
"Of all the global environmental changes, the most critical is biological extinction," he continued. "For one thing, biological extinction is the only irreversible global environmental change that we can think of. Climatic change, given time and willingness on behalf of governments and society, is something we can fix. It will take time but is reversible."
"When you have the situation that the mammals are not present you don't even notice it, since most mammals are secretive or nocturnal. You tend to think that these forests are in good shape but overlook the fact that something very significant, the fauna, is missing. The absence of these animals indirectly affects the ecology of the forest," he explained.
"Imagine that you were to remove all of the bats from the tropical rainforest. Then many of the plants that rely upon them as pollinators or as dispersal agents for seeds are going to be in trouble. This is relatively straight forward, but it is a little more difficult to think about what happens when the deer, the peccaries, and the tapirs are not there. It's not easy to imagine that they are performing a service to the ecology of the forest, but in fact they are by trampling and preying on seeds and leaves. They are determining the structure of the understory which effectively determines the future of the forest — the impact of mammals on the forest understory is crucial: baby trees will someday grow up to become the forest canopy."
Dirzo says the scale of defaunation is quite dramatic — each year tens of millions of animals are killed in the Amazon, Africa, and Asia. But he stresses the fact that local populations need to feed themselves, either by hunting or selling meat to markets. As such addressing defaunation will require addressing rural poverty — it will not be a simple as putting a fence about forest reserves or reintroducing captive animals to the wild.
He says that payment for ecosystem services like systems currently in place in Costa Rica and Brazil; agroforestry farming techniques; and smarter management of land could help improve the lives in people living in and around forests where much defaunation takes place. Education and conservation are also important components of campaigns to reduce the over-harvesting of wildlife.
AN INTERVIEW WITH RODOLFO DIRZO
Mongabay: How did you become interested in what you do now?
Rodolfo Dirzo: I was born in Mexico and studied plant ecology at the State university in Morelos, which is south of Mexico City. At the university I did a study mapping the vegetation coverage of an area north of Mexico City, which is an important watershed. The study was an eye-opening experience in that it showed the importance of the ecology for maintaining reservoirs for the city. It was also a great example of how ecology is tied to a practical, real-life problem—water conservation.
After my undergraduate work I went to work at UNAM with a prominent tropical professor of tropical ecology, Professor José Sarukhán, who has done a lot of work with tree demography and developing the field stations of Mexico like Los Tuxtlas. I worked in his lab for a number of years and then we decided it was time to go out to do my graduate training. At the time, which was the late 1970s, Mexico did not have a graduate program with a particular emphasis on ecology, so most of us plant ecologists had to leave the country to train. I went to the U.K. to the University of Wales, Bangor. At the time, the late 1970s, the University of Wales was the "Mecca" of plant biology in part due to John Harper, one of the most influential plant ecologists of contemporary times.
Even before I went to Wales I knew I wanted to do my research on ecological and evolutionary perspectives of interactions between plants and animals, asking the question, "To what extent are animals an important ecological and evolutionary force for plants?"
When I was doing those studies in the 1980s and early 1990s it was very obvious to me that the most important interaction was insect herbivory and plants responding to that pressure, producing defensive compounds against insects. I wrote a paper in La Revista de Biologáa Tropical, a publication from Costa Rica, about patterns of herbivory in tropical forests such as Mexico. I concluded the paper noting that most of the herbivory I see in tropical forests was done by insects and discounting the significance of mammals. I wrote that "perhaps mammals are not much more than a decoration of the tropical forest in terms of this ecological interaction." This is interesting because today I think that was a terrible mistake. I've been studying the interaction of plants with mammals — mammals as herbivores and in terms of being an ecological and evolutionary force for the plants. The reason why I came up with that conclusion now has become a very important aspect in my line of research: many tropical forests lack evidence of mammalian herbivory due too that what I call defaunation—the loss of the fauna. In turns out that everything I saw in terms the herbivory of plants by animals was with insects for the simple reason that mammals are not present there.
As I said, my main interest has been to understand the patterns of herbivory, but my original results were biased by the absence of mammals doing the things that they should be doing in the forest, like eating plants, trampling, defecating, and preying on seeds. So when you have the situation that the mammals are not present you don't even notice it, since most mammals are secretive or nocturnal. You tend to think that these forests are in good shape but overlook the fact that something very significant, the fauna, is missing. The absence of these animals indirectly affects the ecology of the forest.
Imagine that you were to remove all of the bats from the tropical rainforest. Then many of the plants that rely upon them as pollinators or as dispersal agents for seeds are going to be in trouble. This is relatively straight forward, but it is a little more difficult to think about what happens when the deer, the peccaries, and the tapirs are not there. It's not easy to imagine that they are performing a service to the ecology of the forest, but in fact they are by trampling and preying on seeds and leaves. They are determining the structure of the understory which effectively determines the future of the forest — the impact of mammals on the forest understory is crucial: baby trees will someday grow up to become the forest canopy. My first paper on Defaunation looked at this — the idea of the "empty forest" was effectively popularized by the great tropical ecologist Kent Redford in his famous paper in Bioscience —.
Mongabay: Can you give an example of an ecological process that is disappearing in some forest sites?
Rodolfo Dirzo: In my case, the obvious example is herbivory, the consumption of leaf tissue on the part of animals. On average if you measure how much leaf area is taken by animals, it's about 10 percent in most tropical forest sites that have been studied. That's looking at plants at the mid-stratum level. If you look at the plants in the understory, which are the plants that are going to regenerate the trees of the forest, the incidence of herbivory is similarly low; I have suspected that levels of herbivory in the understory should be higher: I imagine the impact of the removal of all the tapirs, peccaries, deer is partly responsible of such low herbivory— the loss of all of the animals that should be feeding on foliage in the forest. If you remove those animals, you may be removing an important control agent of the understory. This way, the plants upon which those animals typically feed are going to dominate locally in the understory. Thinking about the future, if that understory continues to be dominated by the few species that should be controlled naturally by these herbivorous animals, then you can predict and subsequently simulate with modeling that the forest of the future is likely to be affected by the absence of the animals. The loss of these animals, which are essentially the control agents of the understory, can bring about the local extinction of ecological processes such as herbivory.
Defaunation by humans tends to be a very selective process, where medium and large animals are the most hunted, while the small animals are ignored. Larger animals also tend to be less resistant to fragmentation and deforestation than the smaller ones. The situation that develops is that in the absence of the medium and large mammals, large seeds will not be eaten and therefore will dominate the understory, while seeds eaten by small rodents (the least impacted by fragmentation) will face heavy predation pressure. Such selective defaunation creates a new selective force for evolution of the forest: no attack on the large seeds, and heavy attack on the small seeds. In other words, humans are altering the structure and composition of the forest merely by hunting. So we can see, defaunation is a very serious problem.
Mongabay: In 2003 you co-authored a review on extinction with Peter Raven of the Missouri Botanical Garden. Can you highlight some of the key points?
Rodolfo Dirzo: One of the major conclusions was that global environmental change was not only climate change. Of course climate change is very important and well-known form of change, but there are others, including land use change; fragmentation, which is the change in the spatial configuration of the forest. And those environmental changes affect biodiversity quite significantly. Perhaps the important corollary to the paper I wrote with Peter Raven is that of all the global environmental changes, the most critical is biological extinction: For one thing, biological extinction is the only irreversible global environmental change that we can think of. Climatic change, given time and willingness on behalf of governments and society, is something we can fix. It will take time but is reversible.
There was another point which connects with the different types of global change: land use and overexploitation are driving local extinction of plant and animal species.
Now what can we do about that? It's really a complex situation. On one hand, habitat fragmentation has a very important connection to defaunation. Forest remnants are incapable of maintaining viable populations of many medium and large animals. Another element is that by fragmentation areas that were once more or less remote are now more accessible to hunters. In other words, fragmentation exacerbates hunting pressure.
Mongabay: What are the approaches for slowing defaunation?
Rodolfo Dirzo: One strategy would be to reconnect fragmented habitats. Just as we talk about reforestation we could talk about refaunation. Technically there are a number of difficulties that we ecologists need to be working on. For example, a refaunation program at my study site at Los Tuxtlas would face these technical questions: Where do we bring the animals back from? Do we bring them from Chiapas? Costa Rica? There may be genetic differences between distinct populations of the same species. The second big issue is quarantine. How do we ensure that if we bring animals back, we do not unleash an epidemic disease. Third, and most critical, is that any reintroduction will fail if the local community is not involved. Without informing local people of the program, engaging them and having them appreciating the relevance of a refaunation program, the re-appearance of more animals might just drive more hunting. We need to combine reintroduction with a very strong program of involvement of the local communities—why the harpy eagle, tapir, and bat are important and should not be hunted. We need to articulate the concrete local benefits from converting an empty forest to one with all of its flora and fauna. People need to eat and have a dignified life. People need to be compensated for the giving up their needs or rights to hunt and exploit the forest and for their efforts to maintain biodiversity. Payments for environmental services—like the payment system in Costa Rica—may be one vehicle for compensation.
Agroforestry can maintain vegetation biodiversity, prevent erosion, and diversify income. Mimicking the structure of the rainforest using economic species—fruit trees, bananas, coffee, cacao, and timber species—can improve the well-being of local communities. For example, the canopy strata could be made of valuable timber trees; the medium strata of fruit trees; the understory of cacao and coffee; and a lower understory of decorative palms, orchids, and vanilla. It's just a matter of organizing a system for land use. It could include areas that have been heavily impacted and intensively managed by the farmers.
In the Yucatan Peninsula there is an encouraging example in the Forest Pilot Program in Quintana Roo, which is focused on exploiting timber on a sustainable basis. The program, which is run as a cooperative of local farmers, has a rotational system where they use one piece of forest and only harvest trees of a given size. Using some technical assistance, they know how long it takes for the forest to regenerate harvestable timber and replant the trees they remove. It proves to be a very efficient system of forestry management and shows it can actually be profitable to sustainably harvest trees in this mosaic. The program promotes secondary products including furniture which have a higher value than the raw timber.
Mongabay: What about intensification, for example, going from 1 head of cattle per hectare to six? What about iguana farming or some way to augment the availability of protein using native species that are better adapted to the local environment?
Rodolfo Dirzo: People have looked at peccaries which can be managed more intensively. Iguana is another possibility—Panama is doing this. Certainly that can be done.
Mongabay: Are you seeing more commercial hunting now? Hunting for markets rather than subsistence?
Rodolfo Dirzo: Yes, there is both subsistence and commercial hunting. Most commercial hunting is illegal, but it seems to be increasing. The availability of weapons makes hunting easier.
There is also the market for live animals for consumption and the pet trade. For example the Peruvian town of Iquitos has a remarkable diversity of animals in its markets—both live animals and skins. Between 1982-1986, 1.4 million animals or animal skins were exported just from Iquitos.
Finally we have the removal of animals for biomedical research.
The take home point is satellite images don't show defaunation. When you visit these forests it is really shocking to see the intensity of animals being harvested. It's not just that these animals are charismatic—we now know that they play a critical ecological role in the health and structure of the forest and community as a whole. Defaunation is becoming a critical biodiversity conservation issue.
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