“Hyperalarming” study shows massive loss of insect populations and corresponding declines in lizards, frogs, and birds – “Everything is dropping”

Desdemona Despair

By Ben Guarino
15 October 2018

(The Washington Post) – Insects around the world are in a crisis, according to a small but growing number of long-term studies showing dramatic declines in invertebrate populations. A new report suggests that the problem is more widespread than scientists realized. Huge numbers of bugs have been lost in a pristine national forest in Puerto Rico, the study found, and the forest’s insect-eating animals have gone missing, too.

In 2014, an international team of biologists estimated that, in the past 35 years, the abundance of invertebrates such as beetles and bees had decreased by 45 percent. In places where long-term insect data are available, mainly in Europe, insect numbers are plummeting. A study last year showed a 76 percent decrease in flying insects in the past few decades in German nature preserves.

The latest report, published Monday in the Proceedings of the National Academy of Sciences, shows that this startling loss of insect abundance extends to the Americas. The study’s authors implicate climate change in the loss of tropical invertebrates.

“This study in PNAS is a real wake-up call — a clarion call — that the phenomenon could be much, much bigger, and across many more ecosystems,” said David Wagner, an expert in invertebrate conservation at the University of Connecticut who was not involved with this research. He added: “This is one of the most disturbing articles I have ever read.”

Bradford Lister, a biologist at Rensselaer Polytechnic Institute in New York, has been studying rain forest insects in Puerto Rico since the 1970s. If Puerto Rico is the island of enchantment — “la isla del encanto” — then its rain forest is “the enchanted forest on the enchanted isle,” he said. Birds and coqui frogs trill beneath a 50-foot-tall emerald canopy. The forest, named El Yunque, is well-protected. Spanish King Alfonso XII claimed the jungle as a 19th-century royal preserve. Decades later, Theodore Roosevelt made it a national reserve, and El Yunque remains the only tropical rain forest in the National Forest system.

“We went down in ’76, ’77 expressly to measure the resources: the insects and the insectivores in the rain forest, the birds, the frogs, the lizards,” Lister said.

He came back nearly 40 years later, with his colleague Andrés García, an ecologist at the National Autonomous University of Mexico. What the scientists did not see on their return troubled them. “Boy, it was immediately obvious when we went into that forest,” Lister said. Fewer birds flitted overhead. The butterflies, once abundant, had all but vanished.

García and Lister once again measured the forest’s insects and other invertebrates, a group called arthropods that includes spiders and centipedes. The researchers trapped arthropods on the ground in plates covered in a sticky glue, and raised several more plates about three feet into the canopy. The researchers also swept nets over the brush hundreds of times, collecting the critters that crawled through the vegetation.

Each technique revealed the biomass (the dry weight of all the captured invertebrates) had significantly decreased from 1976 to the present day. The sweep sample biomass decreased to a fourth or an eighth of what it had been. Between January 1977 and January 2013, the catch rate in the sticky ground traps fell 60-fold.

“Everything is dropping,” Lister said. The most common invertebrates in the rain forest — the moths, the butterflies, the grasshoppers, the spiders, and others — are all far less abundant.

“Holy crap,” Wagner said of the 60-fold loss.

Louisiana State University entomologist Timothy Schowalter, who is not an author of the recent report, has studied this forest since the 1990s. The new research is consistent with his data, as well as the European biomass studies. “It takes these long-term sites, with consistent sampling across a long period of time, to document these trends,” he said. “I find their data pretty compelling.” [more]

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‘Hyperalarming’ study shows massive insect loss

By Mary L. Martialay
15 October 2018

(RPI) – 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 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.”

“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 eightfold from 1976 to 2013.
• As arthropods declined, simultaneous decreases occurred in Luquillo’s insectivorous lizards, frogs, and birds.
• The authors also compared estimates of arthropod 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 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.

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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 Autónoma de México, was co-author on the study, which was funded by the National Science Foundation.

Research into the effects of climate 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.

Two Degrees Decimated Puerto Rico’s Insect Populations

ABSTRACT: A number of studies indicate that tropical arthropods should be particularly vulnerable to climate warming. If these predictions are realized, climate warming may have a more profound impact on the functioning and diversity of tropical forests than currently anticipated. Although arthropods comprise over two-thirds of terrestrial species, information on their abundance and extinction rates in tropical habitats is severely limited. Here we analyze data on arthropod and insectivore abundances taken between 1976 and 2012 at two midelevation habitats in Puerto Rico’s Luquillo rainforest. During this time, mean maximum temperatures have risen by 2.0 °C. Using the same study area and methods employed by Lister in the 1970s, we discovered that the dry weight biomass of arthropods captured in sweep samples had declined 4 to 8 times, and 30 to 60 times in sticky traps. Analysis of long-term data on canopy arthropods and walking sticks taken as part of the Luquillo Long-Term Ecological Research program revealed sustained declines in abundance over two decades, as well as negative regressions of abundance on mean maximum temperatures. We also document parallel decreases in Luquillo’s insectivorous lizards, frogs, and birds. While El Niño/Southern Oscillation influences the abundance of forest arthropods, climate warming is the major driver of reductions in arthropod abundance, indirectly precipitating a bottom-up trophic cascade and consequent collapse of the forest food web.

SIGNIFICANCE: 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. We 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. If supported by further research, the impact of climate change on tropical ecosystems may be much greater than currently anticipated.

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Climate-driven declines in arthropod abundance restructure a rainforest food web