A large-scale new study identifies a critical threshold for significant species loss in the Amazon due to deforestation, but also suggests a strategy for action
The deforestation of the Amazon is reaching a critical point for maintaining biodiversity. A year-long study of 3 million hectares in Brazil’s southwestern state of Rondôni revealed that each loss of 10 percent of forest cover meant the extinction of one or two species. But when 43 percent of forest cover is lost, this becomes a threshold where the risk to biodiversity increases rapidly – with each extra 10 percent of disappearing forest cover, the species lost accelerates to between two and eight.
The research team, lead by Dr Jose Manuel Ochoa-Quintero from Cambridge University’s Department of Zoology, estimate that about a third of the Amazon region is heading to, or is already at, this threshold point, and that unless urgent action is taken these areas will lose between 31-44% of species by 2030.
The problem of deforestation is exacerbated by the fact that the species in the patches or fragments of forest that remain, have reduced connectivity with the habitats that maintained them. ‘We’re checking to see whether the reason why some of the species disappear is because interaction is being lost in the process of forest fragmentation,’ explains Dr Ochoa-Quintero. ‘You lose the connection between the subpopulation and the different remaining native vegetation. And also within those remaining areas, you are losing interaction so it may entail losing species.’
Underlying dynamics of species loss
The complex interactions where species feed off other species, or species which depend on other species to produce seeds or for pollination, begins to unravel. ‘All these species interactions are very important,’ says Dr Ochoa-Quintero. It’s a challenge to track this change he says, because the issue isn’t simply identifying species loss, but also identifying ‘the mechanisms that generate those responses.’
There were two sources of data. Dr Ochoa-Quintero spent a year with an assistant driving around this three million hectares area which they divided into 1,223 squares of 10,000km, selecting 31 squares representative of the spectrum of forest cover across the region. Dr Ochoa-Quintero’s assistant used to hunt in the area and knew the species well. They used traditional observation techniques, logged evidence such as footprints and faeces, and also played recordings of songs to try and elicit responses from small birds who are difficult to see, but are territorial. ‘It’s hard work, the forest is full of mosquitoes,’ reflects Dr Ochoa-Quintero.