Puerto Rican insect populations decimated at two degrees

While the temperature in the tropical forests of northeastern Puerto Rico has risen by two degrees Celsius since the mid-1970s, the biomass of arthropods – invertebrate animals such as insects, centipedes and bed bugs – has been multiplied by 60, according to a new results published today in the Proceedings of the National Academy of Sciences.

The findings corroborate the recent warnings of the United Nations Intergovernmental Panel on Climate Change regarding serious threats to the environment, given a global temperature rise of 2.0 degrees Celsius. As in other tropical regions, the Luquillo Rain Forest study area has already reached or exceeded an average temperature increase of 2.0 degrees Celsius, and the study reveals that the consequences are potentially catastrophic.

"Our findings suggest that the effects of global warming in tropical forests could be even greater than expected," said Brad Lister, lead author of the study and faculty member of the Department of Biological Sciences at the Rensselaer Polytechnic Institute. . "Insect populations in the Luquillo Forest are collapsing and, once this has started, the animals that eat them lack food, resulting in reduced reproduction and survival, and therefore, a decrease in abundance. "

"The climate-induced decline in arthropod abundance is restructuring a rainforest food web" is based on data collected between 1976 and 2013 by the authors and the Luquillo long-term ecological research program in three habitats. average altitude of the protected rainforest of Luquillo in Puerto Rico. Meanwhile, average maximum temperatures rose 2.0 degrees Celsius.

The main conclusions include:

• Sticky traps used to sample arthropods on the soil and in the forest cover indicated a collapse of forest arthropods, with biomass catch rates increasing by a factor of 60 between 1976 and 2013.
• The biomass of arthropods collected using a ground sweep net was also multiplied by eight between 1976 and 2013.
• As arthropods declined, both insectivorous lizards, frogs and Luquillo birds suffered a simultaneous decrease.
• The authors also compared estimates of the abundance of arthropods that they had made in the 1980s in the Chamela-Cuixmala Biosphere Reserve, in western Mexico, with those of 2014 During this period, the average temperature increased by 2.4 Celsius and the biomass of arthropods was multiplied by eight.

Cold-blooded animals living in tropical climates are particularly vulnerable to global warming because they are adapted to relatively stable temperatures all year round. Based on their data analyzes, which included new causality assessment techniques, the authors conclude that global warming is the major factor reducing arthropod abundance in the Luquillo Forest. These reductions resulted in a significant upward trophic cascade and the collapse of the forest food web that ensued.

As tropical forests are home to two-thirds of the world's species, these results have a profound impact on the future stability and biodiversity of tropical forest ecosystems, as well as on conservation efforts to mitigate the effects of forcing. climate.

Andres Garcia, of the National Autonomous University of Mexico, was co-author of the study funded by the National Science Foundation.

Research on the effects of climate change is an exciting aspect of The New Polytechnic, a new paradigm for teaching, learning and research in Rensselaer. The foundation of this vision is the recognition that global challenges and opportunities are so important that they can not be adequately addressed, even by the most talented person working alone. The new polytechnic school transforms the overall impact of research, its innovative pedagogy and the life of Rensselaer's students.

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More information:
Bradford C. Lister et al., "The decline in the abundance of arthropods caused by climate restructures the food web of the rainforest," PNAS (2018). www.pnas.org/cgi/doi/10.1073/pnas.1722477115