El Yunque national forest in Puerto Rico. After bees and birds, insects and other arthropods have also suffered massive losses, a study from a Puerto Rico forest published on Monday showed, citing the impact of climate change. (Shutterstock/Dennis van de Water)
After bees and birds, insects and other arthropods have also suffered massive losses, a study from a Puerto Rico forest published on Monday showed, citing the impact of climate change.
Measuring the population of arthropods, which includes insects, caterpillars, and spiders, is not simple but one method is to place sticky traps on the ground and in the forest canopy.
Researchers can also pass nets hundreds of times over the ground or in the foliage before weighing the dry captured biomass.
That is what the biologist Bradford Lister did in 1976 and 1977 in El Yunque National Forest in the US Caribbean commonwealth of Puerto Rico.
Lister, of Rensselaer Polytechnic Institute in Troy, New York, returned there with another biologist in 2011 and 2012 to use the same methods.
They found that the dry weight biomass of arthropods captured in sweep samples had declined 4 to 8 times, and 30 to 60 times in sticky traps, according to their findings published in the US Proceedings of the National Academy of Sciences.
This decline was accompanied by parallel reductions in insectivorous lizards, frogs, and birds, according to observations by the researchers.
"Everything is dropping," Lister told The Washington Post, warning of cascading effects on the food chain.
"If the tropical forests go, it will be yet another catastrophic failure of the whole Earth system," he said, "that will feed back on human beings in an almost unimaginable way."
According to the model used by the researchers, the blame lies principally with global warming. They reach this conclusion by noting Puerto Rico's rising temperature over about 40 years.
The mean maximum temperatures, recorded by a forest weather station, increased 2 C between 1978 and 2015.
Several studies around the world have presented evidence of a reduction in insect biodiversity, and of other animal families.
But the effect of climate change is not uniform.
A study published in the journal Science in August concluded that, except in tropical regions, an increase in temperature was on the contrary going to stimulate the population of harmful insects which will proportionately ravage more humans.
Avoiding global climate chaos will require a major transformation of society and the world economy that is "unprecedented in scale," the United Nations said in a landmark report last week.
It warned that the world must become "carbon neutral" by 2050 to have at least a 50/50 chance of keeping global warming below 1.5 C.