Here's what's devastating Puerto Rico's insect populations—and the animals that eat them. The effects spell peril for the entire food web.

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Very few studies have tracked declining population trends across all species, not just insects. Anole lizards, shown above, are a natural predator of arthropods; their average density in the area studied was cut by more than half.
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▼ The world is getting warmer, but insect populations are not doing so hot. Plenty of studies have shown how certain bugs like beesand fireflieshave hemorrhaged numbers over the last several decades. But until now, very few have tracked these trends across all species. As it turns out, things are stupendously worse than we previously thought, and the culprit is—spoiler alert—climate change.
New findings published Monday in  the Proceedings of the National  Academy of Sciencesillustrate how insect and other arthropod populations in the rain forests of Puerto Rico have declined 60-fold over the last four decades; this time span saw a 2 degree Celsius rise in average temperatures. Moreover, the effects are already cascading into losses for the animals that prey on these bugs for food, threatening to crash the intricate food web that sustains and stabilizes the rainforest ecosystem.
“We are not seeing any studies that show that insect groups are doing particularly well,” says Scott Black, the Executive Director for the Xerces Society for Invertebrate Conservation. “This is just the latest study in a long line that show loss and decline of invertebrates at the population level, species level, and loss of invertebrate biomass generally.” Black is not particularly surprised by the new findings, except in how severe the results describe that loss, and that’s part of what makes this latest study so uncomfortable to swallow.
Lead study author Bradford Lister, a biologist at Rensselaer Polytechnic Institute in New York, has been studying the region’s insect populations for nearly forty years, focusing on the El Yunque national forest, located in northeastern Puerto Rico on the slopes of the Luquillo mountains, and the only tropical rain forest within the U.S. National Forest System. When he began in the 1970s, Lister was measuring and tallying estimates of the forest’s insect populations as well as their predators, including birds, lizards, and frogs.
Four decades later, he came back to take measurements of the insects once again, as well as other arthropod species like spiders and centipedes. (▪ ▪ ▪)

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