Intense droughts and fires during the last El Niño cycle, combined with human activity (mainly cattle ranching), has led to a massive drop in the number of dung beetles in the Amazon. The effects of the drop have lasted at least two years, according to new research.
The study was carried out by an international team at the Lancaster Environment Centre in the United Kingdom.
The El Niño of 2015-16 “delivered a very significant drought and, in combination with human activities such as agriculture, livestock and deforestation, contributed to mega wildfires that burned more than three million hectares of Amazon forests, including a million hectares in just one region,” the researchers say in a press release.
The effects of droughts and wildfires on Amazonia’s trees have been studied for decades, but researchers were less clear about the impacts on fauna and the role they have in ecosystem functioning.
Dung beetles are key for spreading nutrients and seeds, and they are important indicator insects used to gauge the overall health of an ecosystem.
Counting Amazon dung beetles
The international team of scientists from the UK, Brazil and New Zealand counted more than 14,000 dung beetles from 98 species across 30 forest plots in the Brazilian state of Pará, within the Amazon, through several surveys conducted between 2010 and 2017.
They also monitored how much dung was removed and how many seeds were dispersed by dung beetles.
The researchers counted around 8,000 beetles across the plots in 2010. However, in 2016, following the El Niño, numbers had plummeted to around 3,700 and in 2017 they found just 2,600 beetles.
Human disturbance, through activities such as deforestation and predatory logging, significantly increases the flammability of the forests – as forest fires do not occur naturally in the Amazon.
All surveyed forests saw beetle numbers fall, though the results also show that forests that burned had fewer beetles than those areas that had just experienced drought.
“Our investigation provides important insights into how human activities and climate extremes can act together and affect tropical forest biodiversity and ecosystem functioning,” said lead researcher Dr Filipe França from the Lancaster Environment Centre at Lancaster University and associate researcher at Embrapa Amazônia Oriental in Brazil.
The decrease in the number of beetles could also signal a decrease in the number of mammals, who may have died in the fires, since the insects depends on their poo for nesting and feeding, the researcher adds.
This thesis is corroborated by a previous study that shows that mammal presence has a large influence on dung beetles.
Another problem with the loss of beetles is that it may be harder for forest to regenerate after extreme drought and fire events.
“We found far fewer dung beetles after the El Niño event, and those that survived were struggling to do their work of spreading nutrients and seeds in forests already impacted either by drought alone or in areas that also experienced fires”, explained Professor Rodrigo Fadini from the Federal University of Western Pará in Brazil.
“Taken together, the research findings suggest that human activities can interact with climate extremes in different ways and that, combined or not, these disturbances can threat the delicate balance of tropical forest fauna, including insects, and their key contribution to ecosystem processes,” the researchers note.