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Temperature change wreaks havoc on Puerto Rico insect populations

By on October 16, 2018

SAN JUAN – While temperatures in the tropical forests of northeastern Puerto Rico climbed 2 degrees Celsius (3.6 degrees Fahrenheit) since the mid-1970s, the population of arthropods– invertebrate animals such as insects, millipedes and sowbugs–declined by as much as 60-fold, according to new findings published 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 degree Celsius elevation in global temperature. Like some other tropical locations, the study area in the El Yunque National Forest in Luquillo has already reached or exceeded a 2 degree Celsius rise in average temperature, and the study found that the consequences are potentially catastrophic.

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“Our results suggest that the effects of climate warming in tropical forests 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.”

The study, “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 habitats in Puerto Rico’s protected Luquillo rainforest. During this time, mean maximum temperatures have risen by 2 degrees Celsius.

Another major finding is that as arthropods declined, the number of Luquillo’s insectivorous lizards, frogs, and birds declined.

“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 climate warming 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 forest 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,” reads a release issued by Rensselaer Polytechnic Institute.

Rensselaer faculty and alumni represent 86 members of the National Academy of Engineering, 18 members of the National Academy of Sciences, 26 members of the American Academy of Arts and Sciences, 8 members of the National Academy of Medicine, 8 members of the National Academy of Inventors, and 5 members of the National Inventors Hall of Fame, as well as 6 National Medal of Technology winners, 5 National Medal of Science winners, and a Nobel Prize winner in Physics.

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

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