The study, undertaken by scientists from Brazil and the UK, looked at 18 mammal species in 196 forest fragments, and compared their current populations to estimates of their population densities before Europeans colonised the region about 500 years ago.
The results of the study, published in the journal PLoS One, showed that mammals are being lost from forest fragments at least twice as fast as previous estimates suggested.
Of over 3,500 mammal populations estimated to have originally lived in the study area, only about 22% remain today. Among the species being lost are large, charismatic mammals such as the jaguar, lowland tapir, northern muriqui and giant anteater, while the white-lipped peccary has been completely wiped out in the region.
Only 3 of the 18 species studied – two small monkeys and an armadillo – were still present across the whole area.
“We uncovered a staggering process of local extinctions of mid-sized and large mammals,” said Dr Gustavo Canale of the State University of Mato Grosso (UNEMAT), one of the authors of the study.
The Atlantic forest is one of the most diverse and biologically rich forests in the world, with many of its species found nowhere else. However, it is also one of the world’s most highly threatened ecosystems, with only 8% of its original cover remaining.
Centuries of logging, urbanisation and clearance for ranches, agriculture and plantations have left only small fragments of forest intact, and what remains is often degraded. Forest fragments are also highly accessible to hunters, as well as being vulnerable to fires and to ‘edge effects’, which include increased exposure to winds and drought.
According to Dr Canale, the presence of the mammals in the study could not be predicted by the size of the forest fragment, with even large patches of forest lacking many species. On average, only 4 of the target mammal species were found in each forest fragment, and none of the sites studied contained all 18 species.
Previous estimates of mammal populations assumed that large areas of forest would be able to support more species, but failed to take into account the combined effects of multiple threats.
“You might expect forest fragments with a relatively intact canopy structure to still support high levels of biodiversity,” explained Carlos Peres, another of the authors of the study. “Our study demonstrates that this is rarely the case, unless these fragments are strictly protected from hunting pressure.”
These findings, which suggest that even large forest fragments are not enough to save many mammals from local extinction, raise concerns for tropical forests around the world, many of which are becoming increasingly fragmented.
The study found that mammals only fared better in official protected areas such as national parks, where forest fragments are large and hunting is banned. The team therefore recommends that more protected areas are needed and that their protection should be strictly enforced.
Unfortunately, only a tiny fraction of the Atlantic forest currently has protected status, and the Brazilian government is under pressure from farmers to reduce forest protection. A final vote on changes to the government’s Forest Code is expected by the end of August.
According to Jean Paul Metzger, an ecologist at the University of São Paulo who was not involved in the study, “The new bill doesn’t explicitly stimulate deforestation, but it doesn’t impose forest restoration either. That means protected areas are likely to remain isolated, which in turn may mean more extinctions in the future.”
Read more about the Atlantic forest on ARKive.
Liz Shaw, ARKive Species Text Author