Thursday, April 4, 2013

Jaguars in the Pantanal

by Nick Cunningham

In the last post, Duncan wrote about the Pantanal, the largest wetlands in the world, which is located mostly in Brazil, but also in Bolivia and Paraguay. Not only does the Pantanal provide multiple ecosystem services with real economic value - flood and erosion control, filtering pollutants, and cleaning and provisioning water - but the Pantanal is home to a rich diversity of wildlife. 

The Pantanal (photo credit: Alicia Yo)
One phenomenon that I have been interested in lately is the role of "keystone species," - those species that play a critical role in maintaining a healthy ecosystem. Keystone species are often in the form of "top predators" or "Apex Predators," and as I discussed in a post about sharks, top predators exert enormous influence over how ecosystems operate. If their populations decline, it can have "trophic cascades," or ripple effects down the food chain. Sharks for example, eat weak and sick fish, allowing healthy individuals to survive and pass on healthy traits. Sharks also eat species that graze marine habitats, keeping overgrazing in check. These are essential functions for the ecosystem, and when the predators disappear, fish populations become less healthy and seabeds are overgrazed.

Just as sharks are important for marine ecosystems, top terrestrial predators are key for their habitats. In the Pantanal, for example, jaguars are considered to be a top predator. Jaguars range from Mexico down to Argentina, and live in dense vegetation and along riverbanks. They eat medium-sized animals like deer, foxes, and  animals in Brazil such as capybaras, tapirs and peccaries. Scientists believe the declining numbers of jaguars are an enormous concern - absent the top predator, negative effects can ripple downwards.

In fact, the notion of "top-down" control in ecosystems, as opposed to "bottom-up" has only recently emerged as a leading theory on how ecological systems are governed. Up until now, many in the scientific community believed that life worked upwards, beginning with photosynthesis and and plant life. However, recent studies point to the belief that Apex Predators may in fact be more important, and their absence can cause ecosystems to breakdown. The science is still controversial. But, the role of predators is becoming better understood as they begin to disappear. Caroline Fraser wrote an excellent article  on Yale's E360 blog, which outlines this debate. Here is a quick quote:

"Beginning with aquatic experiments, they have amassed considerable evidence of damage done to food chains by predator removal and have extended such studies to land: Predation may be as consequential, if not more so, than bottom-up forces. With a comprehensive new book (Trophic Cascades) and a major Science review published this summer, these specialists present the case that our persecution of predators menaces the marine and terrestrial ecosystems that produce food, hold human and zoonotic diseases in abeyance, and stabilize climate.

Using such terms as “deep anxiety” and “grave concern” to signal their alarm, the authors contend that the loss of large animals, and apex predators in particular, constitutes humanity’s “most pervasive influence” on the environment. It amounts, they argue, to a “global decapitation” of the systems that support life on Earth."

Photo: Smithsonian
As I mentioned, jaguars play the role of Apex Predator in the Pantanal, keeping the population of a variety of smaller animals in check. However, the extent to which the ecosystem will suffer negative effects from its absence is unknown - scientists have much to learn about jaguars. They are elusive and solitary, and as such, much of the research on jaguars underway seeks to merely map out their basic behavior and understand how they interact with other species in their habitat.
But, scientists are racing against the clock as jaguar populations are already declining. The largest reason is because of habitat fragmentation (i.e. deforestation). In the Pantanal, jaguar's also face an additional threat - being hunted by ranchers who are concerned about jaguar's killing their cattle. Conservationists have been working to protect the jaguar, setting up a "Jaguar Conservation Fund," that compensates ranchers if jaguar's kill their cattle. In return, ranchers are prohibited from killing jaguars. Early results are promising.

Caroline Fraser also published a book, "Rewilding the World," and discusses efforts to expand the jaguar's habitat. The idea is to create corridors between the Pantanal and the Cerrado, a dry savanna-like biome in Brazil that borders the Pantanal. Much the Golden Lion Tamarins in the Atlantic Forest, jaguars need connected habitat in order to survive over the long-term. Reversing the trend of destroying ecosystems for agricultural development and cattle ranching, and then building back forests and wetlands to allow these species to survive, is a monumental challenge. But, in order for ecosystems like the Pantanal to remain healthy and productive, it must be done.

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