World Wildlife Fund

By Dr. Eric Dinerstein

In the 20th century, the average man, woman or child has at best rare occasions to encounter the world’s largest carnivorous and herbivorous mammals in their natural habitats. One reason is that many of these large wild animals are undergoing range collapse, with less and less natural habitat available to them. When the range collapses, the species disappears. As scientists, we are always looking for what we call indicator species – ones that are so sensitive to environmental change that they serve as valuable sentinels of impending ecological disaster. Their rapid decline or disappearance is a danger signal to those observant enough to heed the warning.

Increasingly, field studies of large carnivorous and herbivorous mammals reveal the extent to which they influence their surroundings. Large predators, such as tigers, lions, jaguars and wolves change the behavior of their prey and in many places control prey populations. Giant herbivores are certified landscape engineers, who through their trampling, browsing, and manuring of ingested seeds shape the landscape. Their loss changes everything. Lions and Tigers and Other Large Mammals WWF scientists, working with other tiger specialists, have documented this phenomenon of range collapse for tigers, adding to existing research showing that lions, Asian elephants, and all five rhino species have been wiped out over vast areas of their former distribution.

Large mammals are particularly prone to local extinction because they are targets for the burgeoning trade in wild meat, they are controlled by humans as competitors for the natural resources of field and forest, or they are brutally poached to obtain their body parts. Many large species are also sensitive to habitat fragmentation that isolates populations into small secluded areas. These isolated populations shrink and eventually wink out, never replenished with new colonists from once-neighboring areas now distant and removed.

A New Investigation Begins Two years ago several colleagues and I began pondering the question: If large mammals are so important to ecosystem health, and many species are undergoing dramatic range contractions, how many wild places still retain their full complement of native large mammals?

At the time, I was in the field with natural history companions David Wilcove of Princeton University and John Morrison of WWF. We were crossing Sierra de Canastra National Park in the vast savanna region of Brazil known as the Cerrado, where we had been on the lookout for this region’s unique large mammals: tapirs, maned wolves, giant anteaters and giant armadillos.

Our guide, Edson Enrigo, spotted one of our quest species, a maned wolf, being followed by a spectacular aplomado falcon. It was as if we were watching part of some Brazilian fable of species interaction: The maned wolf scared up insects in its wake that the falcon swooped to catch, and the falcon looked out for jaguars and pumas that might not appreciate a long-legged wolf intruding into their territory.

As the fable played out in front of us, we considered what the ranges once might have been of maned wolves and their grassland companions, giant anteaters. Along the rolling hills of grass we kept our eyes peeled for large, overripe bananas – the search image we use to recognize a giant anteater from a distance. Armed with this tip, we sighted several and approached. On foot and downwind we got to within 20 feet of one of these hairy-splendored creatures.

Swift-Footed Rheas and Their Followers Later, back in the van, we spotted a group of rheas, the South American relative of the ostrich, as they ran across the road. They were gone so fast that John didn’t have a chance to see them. Since this would have been his first rhea sighting, he darted out of the moving van to chase the opportunity. Easily one of the fastest WWF employees and a former national Ultimate Frisbee champion, John was still no match for the rheas.

When he got back, winded and disappointed, we returned to our developing idea of asking which places on Earth still had not only their maned wolves and giant anteaters, but the same roster of large mammal species they had, say, 500 years ago.

Once breathing normally, John stepped up to lead the inquiry on a formal, scientific basis. We called it WILMA, short for World’s Intact Large Mammal Assemblages. We chose the title WILMA because we were all interested in prehistoric large mammals and we all grew up watching the Flintstones cartoons.

From Inquiry to Research Results All joking aside, some serious historical data mining and computer work lay ahead.

We compared current ranges of the largest 263 terrestrial mammals against their distributions in 1500 AD. Large mammals were defined as those with a body mass of over 44 pounds, the mass at which the carnivores’ diet typically switches from invertebrates to larger prey.

The year 1500 AD was chosen as the baseline because colonization began to increase significantly around this year, unleashing the most profound influences of human beings on nature ever recorded prior to the Industrial Revolution. Additionally, as only seven large mammal species have become extinct since 1500 AD, there are opportunities for active conservation of the remaining species.

Our results put the role of some Cerrado parks, such as Emas National Park, in perspective, as some of these still have the full roster of large mammal species they had 500 years ago.

Perhaps the most striking result of our study is that only 21 percent of the Earth’s terrestrial surface still contains all of the large mammals it once held. The 108 places that make up this percentage are either small and intensively managed reserves, such as Kruger National Park in South Africa or Yellowstone National Park, or they are places of extremes such as Siberia and other remote areas too hot, dry, wet, frozen or swampy to support intensive human activities.

The 20 species with the greatest range contraction are habitat generalists and include tigers, elk, American bison, leopards, lions and wolves. The species that has undergone the greatest loss of habitat is, rather surprisingly, the elk. This is accounted for in part by the fact that the elk’s range is historically greater than any other species. In terms of percentage of reduction, the largest impact of human settlement and agriculture has been on the range of the wild horse.

Geographically, Australasia (Australia, New Guinea and neighboring islands) fares best, holding 68 percent of the large mammals it once held, while Indomalaya (the South Asian subcontinent and Southeast Asia) fares worst with only 1 percent. We also found that range collapse in a previously widely occurring species is often associated with species now listed by IUCN as vulnerable or threatened, with some exceptions, including the elk.

From Research to Priorities The obvious question we always ask ourselves is “How does this new information help us?” The answers are several. First, we can now pinpoint places where large mammal assemblages still play important roles in terrestrial ecosystems. Second, we now have targets where, through strategic reintroductions (such as returning wolves to Yellowstone), we can restore intactness in places missing one or two species and recover the ecological fabric of these important conservation landscapes. Third, a number of the key geographic areas identified by this study – such as North America’s Northern Great Plains, the Eastern Himalayas, and Namibia – deserve continued long-term conservation support. The goal is to not just restore the roster of species found there but to bring back the sizes of their populations to the point where they can again play their important ecological roles.

Habitats without their large mammals look markedly different than places where large mammals still occur. Anyone who doubts this phenomenon should visit Yellowstone National Park to see the effect wolves have had on elk populations. Elk, once oblivious to predators, now live in what one ecologist has termed “the landscape of fear” where they no longer frequent places like the aspen groves to feed on the nutritious forage because wolves ambush them. The recovery of these forest zones is a clear lesson as to how important it is to restore the interactions of large mammal species and their habitats – natural interactions that evolved before we ever set foot on the planet and that are disappearing before our eyes.