A disturbing new study finds that global warming helped drive as much as a 60-fold decline in insect population in Puerto Rico’s tropical rainforest between 1976 and 2013.
“Our results suggest that the effects of climate warming in tropical forests may be even greater than anticipated,” said lead author, biologist Brad Lister, of Rensselaer Polytechnic Institute (RPI).
And that’s a potentially catastrophic problem given that the forest saw 3.6°F (2°C) warming during that time — yet warming this century is on track to be far greater.
These new findings follow several studies in recent years that found collapsing insect populations around the world.
A 2014 review of scientific literature and data in the journal Science found the number of insects “such as beetles, butterflies, spiders and worms has decreased by 45 percent” since 1980. The reason: “loss of habitat and global climate disruption.”
And a 2017 Dutch study found that in the past three decades, a stunning three-fourths of the total insect population was lost in 63 protected nature reserves in Germany. The decline was even bigger in mid-summer. The researchers speculate that pesticides may have played a role in the decline — but the RPI biologists argue in their new study that the Dutch scientists “did not thoroughly analyze a number of climate-change variables.”
The RPI researchers explain why pesticides did not cause the insect crash in their study in the Proceedings of the National Academy of Sciences published Monday: “Due to the ongoing reduction in agriculture and associated farmland, pesticides use in Puerto Rico also fell up to 80% between 1969 and 2012.”
They note that cold-blooded creatures, such as insects, “living in tropical climates are particularly vulnerable to climate warming since they are adapted to relatively stable year-round temperatures.” So what seems like a small increase in average temperatures can be devastating.
Along with the insect crash in Puerto Rico, the study found “synchronous declines in the lizards, frogs, and birds that eat” the insects. The study’s bottom line: “Climate warming is the driving force behind the collapse of the forest’s food web.”
The researchers also found a similarly devastating drop in insect population in a tropical dry forest in western Mexico. Between the late 1980s and 2014, the temperature rose in 2.4°C (4.3°F) in this biosphere research — and “we found an eightfold decrease in the dry-weight biomass” of the insects caught in ground traps daily.
What’s especially worrisome about the sharp decline in insects in so many places is that insects play an essential role in the food chain. They also provide crucial services such as pollinating crops.
So these findings are “a real wake-up call — a clarion call — that the phenomenon could be much, much bigger, and across many more ecosystems,” invertebrate expert David Wagner (who was not involved in the study) told the Washington Post.
He added, “This is one of the most disturbing articles I have ever read.”