Two degrees decimated Puerto Rico's insect populations

Credit: CC0 Public Domain

While temperatures in the tropical forests of northeastern Puerto Rico have climbed two degrees Celsius since the mid-1970s, the biomass of arthropods—invertebrate animals such as insects, millipedes, and sowbugs—has declined by as much as 60-fold, according to new findings published today in the Proceedings of the National Academy of Sciences.

The finding supports the recent United Nations Intergovernmental Panel on Climate Change warnings of severe environmental threats given a 2.0 degree Celsius elevation in global temperature. Like some other tropical locations, the study area in the Luquillo rainforest has already reached or exceeded a 2.0 degree Celsius rise in average temperature, and the study finds that the consequences are potentially catastrophic.

"Our results suggest that the effects of climate warming in may be even greater than anticipated" said Brad Lister lead author of the study and a faculty member in the Department of Biological Sciences at Rensselaer Polytechnic Institute. "The insect populations in the Luquillo forest are crashing, and once that begins the animals that eat the insects have insufficient food, which results in decreased reproduction and survivorship and consequent declines in abundance."

"Climate Driven Declines in Arthropod Abundance Restructure a Rainforest Food Web" is based on data collected between 1976 and 2013 by the authors and the Luquillo Long Term Ecological Research program at three mid-elevation habitats in Puerto Rico's protected Luquillo rainforest. During this time, mean maximum temperatures have risen by 2.0 degrees Celsius.

Major findings include:

  • Sticky traps used to sample arthropods on the ground and in the forest canopy were indicative of a collapse in forest arthropods, with biomass catch rates falling up to 60-fold between 1976 and 2013.
  • The biomass of arthropods collected by ground-level sweep netting also declined as much as eight-fold from 1976 to 2013.
  • As arthropods declined, simultaneous decreases occurred in Luquillo's insectivorous lizards, frogs, and birds.
  • The authors also compared estimates of abundance they made in the 1980s in the Chamela-Cuixmala Biosphere Reserve in western Mexico with estimates from 2014. Over this time period mean temperature increased 2.4 Celsius and arthropod biomass declined eightfold.

Cold blooded animals living in tropical climates are particularly vulnerable to climate warming since that they are adapted to relatively stable year-round temperatures. Given their analyses of the data, which included new techniques to assess causality, the authors conclude that is the major driver of reductions in arthropod abundance in the Luquillo forest. These reductions have precipitated a major bottom-up trophic cascade and consequent collapse of the food web.

Given that tropical forests harbor two thirds of the Earth's species, these results have profound implications for the future stability and biodiversity of rainforest ecosystems, as well as conservation efforts aimed at mitigating the effects of climate forcing.

Andres Garcia, of the Universidad Nacional Autònoma de Mèxico, was co-author on the study which was funded by the National Science Foundation.

Research into the effects of change is an exciting aspect of The New Polytechnic, an emerging paradigm for teaching, learning, and research at Rensselaer. The foundation for this vision is the recognition that global challenges and opportunities are so great they cannot be adequately addressed by even the most talented person working alone. The New Polytechnic is transformative in the global impact of research, in its innovative pedagogy, and in the lives of students at Rensselaer.

Explore further

Tropical treetops are warming, putting sensitive species at risk

More information: Bradford C. Lister el al., "Climate-driven declines in arthropod abundance restructure a rainforest food web," PNAS (2018).
Citation: Two degrees decimated Puerto Rico's insect populations (2018, October 15) retrieved 23 September 2019 from
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Oct 15, 2018
Vikings raised cattle, wheat and barley on Greenland for something like 400 years. Too cold today.

Oct 15, 2018
You never hear about the good things warming does.

Oct 15, 2018
This is probably how the Sahara died

Oct 16, 2018
Yeah, the Greenland Vikings gad a good run. A short good run. Then a lengthy miserable, starveling die-off because they weren't smart enough to adapt to Climate Change.

Meanwhile, the despised Skraellings. There before the Easterlings showed up. Adapted to the rude, crude, uncouth savages. Surviving the feckless colony and it's bitter failure. Then thriving through the Little Ice Age.

Since so ,many commentators refuse to learn the methods that made successful colonies thrive? Such as the Great Migration, the Mormons and the Boers.

Perhaps studying the failures such as Viking Greenland, Plymouth, Jamestown or the Hapsburg's could teach what stupid, murderously egotistical mistakes to avoid?

Nahh, not going to happen!

It would mean the commentators cherished comicbooks are wrong.
And Superman won't be showing up to save their sorry asses!

Oct 16, 2018
No evidence for wheat growing in Greenland at all. Zip, zilch, nada. The evidence for barley consists of a few scorched grains in a single layer at the bottom of one trash heap. "The find also substantiates a well-known text from about 1250, 'King's mirror (Konungs skuggsjá)', which mentions in passing that the Vikings attempted to grow grain on Greenland. It is the only report about cultivating barley that we have from that time and says: "As to whether any sort of grain can grow there, my belief is that the country draws but little profit from that source. And yet there are men among those who are counted the wealthiest and most prominent who have tried to sow grain as an experiment; but the great majority in that country do not know what bread is, having never seen it."" https://ancientfo...eenland/

Oct 17, 2018
No mention of pesticide use?

Oct 17, 2018
"If the corn had been imported, it would have been threshed, so finding parts of grains of barley is a very strong indication that the Vikings grew their own corn," he adds. The find also confirms researchers' theory that the Vikings tried to continue the form of life they knew so well from their original homes.

The Vikings also tried to grow other agricultural crops. Their attempts to grow these crops and barley did not last long, however, as the climate cooled over the next couple of centuries until the Little Ice Age started in the 13th century.


Oct 27, 2018
Cross-species effects of effluent pharma products co-ordinate with temperature variations and breakdown of microplastics not withstanding, emergent decline of social responsibility and rage to display material wealth should be the canary in the coal mine. An entirely novel move to understanding the relationship between living nature and human viability is necessary for survival now; it is abundantly clear.

Nov 26, 2018
Now I am worried, insects are evolutionary adaptable.

And here we have anti-scientists asking for non-existent positive effects from mass extinction level environmental stresses, that come too fast to be useful while humans exist. (We may have a million years; species diversity and so bioproductivity recovers from mass extinctions over a few million years.) The Dumb is Strong in those ones.

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