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 February 11, 2020
Hotter, drier El Niños linked to insect decline in the Amazon

 Scientists have found that hotter and drier El Niño events are having major impacts on biodiversity in the Amazon rainforest, including causing the collapse of dung beetle populations, an important indicator species used to gauge the health of a larger ecosystem. According to a new study, dung beetle numbers in the Brazilian state of Pará fell by half following the 2015-2016 El Niño event, and stayed low for at least two years afterwards.

A team of scientists from the United Kingdom, Brazil, and New Zealand tracked dung beetles in 30 forest plots scattered throughout Pará from 2010 to 2017. In total, they counted more than 14,000 dung beetles from 98 species. They also monitored how effectively the beetles were moving dung out of the plots, and how many seeds they were dispersing.

In the first year of their study, the researchers counted 8,000 beetles across their plots. In 2016, following a record-breaking El Niño that caused significant drought and contributed to megafires that burned 7.4 million acres in the Amazon, they counted just 3,700 beetles. In 2017, that number had dropped even further to 2,600. While all forests showed a decline in beetles, the scientists found that areas with wildfires had even fewer dung beetles than those that experienced only drought.

The findings provide "important insights into how human activities [such as agriculture and deforestation] and climate extremes can act together and affect tropical forest biodiversity and ecosystem functioning," Filipe França, an ecologist at Lancaster University and Embrapa Amazônia Oriental in Brazil and lead author of the new study, said in a statement. "The loss of these hardworking beetles could indicate a wider problem that many mammals living in the forest may have also succumbed to the drought and fires. Dung beetles depend on mammal's poo for nesting and feeding, therefore declines in beetles are likely associated with the loss of mammals due to that El Niño drought and fires."

The findings, published in the journal Biotropica earlier this month, are the latest example of the collapse in insect populations worldwide as the world warms and human activities impact ecosystems.