Yellow and white garden lizard
Lizard and bird densities in the research area have been halved. Photo: garden lizard, Sri Lanka ©Tony Neilson)

Tropical forest food chains are collapsing

A new scientific study of insect populations should have alarm bells ringing in every corner of the globe.

Imagine you are in a Puerto Rican rainforest, or the dry tropical forest and rolling plains of the Chamela-Cuixmala nature reserve of Mexico. What do you hear?

Probably very little.

According to a just-published report in the Proceedings of the National Academy of Sciences (PNAS), climate-driven declines in arthropod abundance is dramatically altering the rainforest food web.

Arthropods (invertebrates, including insects that have external skeletons), are declining at an alarming rate. While the tropics harbor the majority of arthropod species, little is known about trends in their abundance.

Biomass crash

Researchers Bradford Lister and Andres Garcia compared arthropod biomass in Puerto Rico’s Luquillo rainforest with data taken during the 1970s and found that biomass had fallen 10 to 60 times.

“Our analyses revealed synchronous declines in the lizards, frogs and birds that eat arthropods. Over the past 30 years, forest temperatures have risen 2.0 °C, and our study indicates that climate warming is the driving force behind the collapse of the forest’s food web,” they say in their National Academy of Sciences report.

They also warn that with more research, the impact of climate change on tropical ecosystems may be much greater than currently anticipated.

Giant stick insect being eaten
When their biomass declines, so do bird numbers. Photo: helmeted friarbird with stick insect, ©Tony Neilson

Arthropods down 99%

Insects and other arthropods in the Puerto Rican study have declined by up to 99% over four decades. Most insect declines have previously been documented in temperate ecosystems and blamed on habitat destruction, insecticides, and climate change.

In 1976–77, one of the authors of the new study surveyed insects and other arthropods in the protected Luquillo rainforest with sticky traps and nets. He returned several times between 2011 and 2013 to see how the populations were faring. He found the weight of arthropods collected in ground traps was 97% less than previously.

50% fewer birds

As their biomass declined, so did numbers of animals that eat them. In their Luquillo study, the researchers found that the average density of anole lizards and insectivorous birds fell by half.

A similar thing happened in the Chamela forest of Mexico when the two researchers compared the abundance of arthropods in 2014 with their previous survey in 1987–88. The average maximum daily temperatures in the Mexican forest had risen by 2.4°C. Ecologists know excessive heat can harm animals, especially those that have evolved to live in relatively constant tropical temperatures.

Meanwhile, politicians in countries like Australia continue to deny the science and refuse to slash CO2 emissions to levels that would slow climate change.

Natural Images 2018

ABOUT THE AUTHOR

©2018 TONY NEILSON All Rights Reserved. All images are protected by Australian copyright law and cannot be downloaded or reproduced without my permission. Please contact me.

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2 thoughts on “NEW RESEARCH

  • Andy A October 31, 2018 at 8:24 AM Reply

    Few governments will act on climate change by themselves. The lead has to come from the people, through the ballot box. It is the only way. If the party you vote for won’t act, you’re voting for the wrong party.

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