The South American Atlantic Rainforest was once home to a "lush … megadiverse" of flora and fauna, according to ecologist Juliano Bogoni. In an article published in the journal PLoS One on September 25, Bogoni and his colleagues report that the collision of the forest with humans has dramatically cut through mammalian populations over the last 500 years.
"We documented thousands of local extermination," writes Bogoni, the newspaper's lead author and currently a postdoctoral fellow at the University of São Paulo in Brazil, in an e-mail.
Stretching from the coastline to mountains in southeastern Brazil, the tropical Atlantic rainforest has shrunk from 425,000 square miles to 55,000 square miles after people cleared away the trees for timber and agriculture and made room for human settlements. The loss and fragmentation of habitat associated with relentless hunting have reduced the numbers of many mammal species, especially large and medium-sized mammal species, and biologists have taken note of dozens of studies in parts of the Atlantic Rainforest.
In addition, we humans have concentrated our agriculture and hunting in the lower-lying areas, which used to have a greater density of mammal species than the higher-lying areas of the Atlantic Rainforest.
"The historical pressure on these landscapes has been enormous," says co-author Carlos Peres, a conservation biologist at the University of East Anglia, where Bogoni earned his doctorate.
So far, however, no one had studied the entire biome of the Atlantic Rainforest to assess the extent of mammalian species bleeding. So Bogoni set about collecting the data from these localized studies and studied nearly 500 different species or "assemblages" of species throughout the Atlantic Forest. At each site, he and his colleagues compared the existing mammalian species from research of the last 30 years with those found around the time Europeans arrived in the area some 500 years ago.
The team found that while not a single mammal was extinct from the entire forest, on average more than 70 percent of the species from each group disappeared.
The researchers also looked beyond biodiversity by analyzing how human activity impacted species grouped by their functions in the ecosystem. Bigger mammals were more likely to be eradicated, probably because they are favored by hunters and reproduce more slowly than smaller animals, Peres said.
The effects of the loss of these important species could spread through the ecosystem, said Bogoni, dismissing the forest's ability to regenerate. Larger herbivores play a crucial role as seed distributors. And the loss of big predators like jaguars could mean that herbivores like capybaras are not kept in check.
"A Margay" – a little wild cat – "is [not] able to boot [on] a Capybara, "says Bogoni. This allows Capybara to increase her population numbers (uncontrollable until they succumb for other reasons). "
In the Amazon, reducing deforestation to save the remaining primary forest is a top priority. But the goals are different for the Atlantic Rainforest, says Bogoni.
"We are not talking about deforestation because there is not much that could be reduced," says Peres. "All attractive forests have already been hammered."
Peres calls for increased rebuilding efforts throughout the Atlantic Forest. Restoration can be expensive, requires the will of political leaders and can have mixed results. Still, it's worth the effort, says Peres. "This is the right time to scratch those parts of nature back and if you can create the habitat, the animals will come."
This story originally appeared on the website of the Global Conservation News Service Mongabay.com, Get updates to their stories delivered to your inboxor follow @Mongabay on Facebook, Instagram or Twitter.