17th October 2018
New study finds massive loss of insects in Puerto Rico
A study by the Rensselaer Polytechnic Institute finds that insect populations in Puerto Rico have crashed since the 1970s. The fall may be caused by rising tropical forest temperatures.
Since the mid-1970s, average temperatures in the tropical forests of northeastern Puerto Rico have risen by 2°C. Meanwhile, 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 this week in the journal Proceedings of the National Academy of Sciences (PNAS).
This study supports a new IPCC warning of severe environmental threats from a 2°C rise in the global temperature and the need for the world's nations to aim for a 1.5°C limit. Like some other tropical locations, the study area in the Luquillo rainforest has already reached or exceeded 2°C and the researchers believe the consequences are potentially catastrophic – not just for insects, but the entire food chain.
"Our results suggest that the effects of climate warming in tropical forests may be even greater than anticipated," says Brad Lister, lead author 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."
Data was collected between 1976 and 2013 by the authors and the Luquillo Long Term Ecological Research program at three mid-elevation habitats in the protected Luquillo rainforest. During this time, mean maximum temperatures increased by 2.0°C.
Major findings included:
Cold-blooded animals living in tropical climates are particularly vulnerable to climate warming, since 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 harbour 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 future effects of climate forcing.
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