A remote area defined by three large rivers appears to harbor more species of mammals than anywhere else on Earth, according to research by the University of Florida and other institutions.
That area lies in the rainforests of northeastern Peru.
Michael Valqui, a doctoral student in the UF Institute of Food and Agriculture Sciences' wildlife ecology and conservation department, began studying the region defined by the Ucayali, Amazon and Yavari rivers in 1994.
Since then, he has confirmed the presence of 86 mammal species, excluding bats. Although some African regions have slightly longer lists, the findings add to a growing body of evidence suggesting that the three-river region has a higher total number of mammal species, since bat diversity is much higher in neotropical rainforests than in African rainforests.
"It's my judgment that this area quite possibly has the highest mammal diversity in the world -- certainly it does for regions of homogeneous habitat," said Robert Voss, curator of mammalogy at the American Museum of Natural History in New York.
Valqui's findings come on the heels of publication of a list by researchers David Fleck and John Harder at Ohio State University that contains 84 mammal species in the same approximately 400-by-100-mile region. Valqui's site is just 62 miles north of the Ohio State site.
"For now, my list is longer, but that may change soon," Valqui said of his findings, which appear in his dissertation. "It is remarkable that two totally unrelated studies come to very similar results almost simultaneously."
Valqui's 15-by-3-mile study area was located near the tiny village of San Pedro about 40 miles south of Iquitos, a large jungle city, and about 270 miles south of the equator in the western Amazon. The UF and Ohio State research sites are composed entirely of lowland tropical rainforest.
Valqui's research initially focused on rodents. After counting 28 rodent species in 1995, he started maintaining a list of all land mammals on the study site. He included mammals he trapped or observed, those identifiable from skulls collected by local hunters and those previously noted by biologists in the same area.
The list has some spectacular entries, such as the giant otter, which can reach 6 feet in length and weigh 60 pounds. It also includes several opossums smaller than a human hand, two extremely rare species of wild dogs and two species of almost comically slow-moving sloths.
Although Valqui didn't identify any new mammals, he did collect three species of rodents that had been found in only one other location. One, a spiny rat, was the most abundant animal in his study area. Spiny rats get their name from their stiff fur, which feels prickly when rubbed backwards.
Valqui and Voss said the region's high diversity is the result of a number of factors.
In general, the Amazon is biologically rich because it is a vast uninterrupted rainforest, they said. Also, the western Amazon tends to be richer than the eastern Amazon.
Scientists hypothesize this diversity results from several factors, including the rapid rise of mountains in the Andes between 3 million and 8 million years ago. The theory is that the rise of the mountains created ridges that isolated animals, allowing them to evolve into distinct species.
In addition, Valqui said, mountain runoff produces richer soils in the western Amazon, allowing higher populations of all species, and decreased extinctions.
As for the three-river region specifically, Valqui said the area's relative proximity to the equator means the annual dry season is nearly nonexistent. Rainfall totals 100 to 110 inches annually, resulting in a steady year-round food source of nuts and fruits for insects, herbivores and the predators that rely on them.
"Seasonal 'bottlenecks' are more pronounced the further you are away from the equator," Valqui said.
Both Valqui and Voss said the true number of nonflying mammal species occupying the region is probably higher than 86 -- perhaps even reaching 100. Valqui said he believes several additional arboreal marsupials and rodents most likely call the region home, but they are extremely difficult to observe because they live high in the canopy.
With no major timber, oil or hydroelectric projects, the three-river region is not considered highly threatened, Valqui and Voss said. Outsiders are forbidden to hunt in the reserve, where Valqui's study site was located, and native subsistence hunting does not pose a major threat to most species, Valqui said.
But the major trends of increasing population density and deforestation pose the same long-term threat as they do to other Amazonian regions, Voss said.
[Contact: Michael Valqui, Aaron Hoover]