https://www.theguardian.com/environment/2019/jan/15/insect-collapse-we-are-destroying-our-life-support-systems
[links and images in online article]
Insect collapse: ‘We are destroying our life support systems’
Damian Carrington Environment editor
Tue 15 Jan 2019 06.00 GMT
Scientist Brad Lister returned to Puerto Rican rainforest after 35 years
to find 98% of ground insects had vanished
“We knew that something was amiss in the first couple days,” said Brad
Lister. “We were driving into the forest and at the same time both
Andres and I said: ‘Where are all the birds?’ There was nothing.”
His return to the Luquillo rainforest in Puerto Rico after 35 years was
to reveal an appalling discovery. The insect population that once
provided plentiful food for birds throughout the mountainous national
park had collapsed. On the ground, 98% had gone. Up in the leafy canopy,
80% had vanished. The most likely culprit by far is global warming.
“It was just astonishing,” Lister said. “Before, both the sticky ground
plates and canopy plates would be covered with insects. You’d be there
for hours picking them off the plates at night. But now the plates would
come down after 12 hours in the tropical forest with a couple of lonely
insects trapped or none at all.”
“It was a true collapse of the insect populations in that rainforest,”
he said. “We began to realise this is terrible – a very, very disturbing
result.”
Earth’s bugs outweigh humans 17 times over and are such a fundamental
foundation of the food chain that scientists say a crash in insect
numbers risks “ecological Armageddon”. When Lister’s study was published
in October, one expert called the findings “hyper-alarming”.
The Puerto Rico work is one of just a handful of studies assessing this
vital issue, but those that do exist are deeply worrying. Flying insect
numbers in Germany’s natural reserves have plunged 75% in just 25 years.
The virtual disappearance of birds in an Australian eucalyptus forest
was blamed on a lack of insects caused by drought and heat. Lister and
his colleague Andrés García also found that insect numbers in a dry
forest in Mexico had fallen 80% since the 1980s.
“We are essentially destroying the very life support systems that allow
us to sustain our existence on the planet, along with all the other life
on the planet,” Lister said. “It is just horrifying to watch us decimate
the natural world like this.”
It was not insects that drew Lister to the Luquillo rainforest for the
first time in the mid-1970s. “I was interested in competition among the
anoles lizards,” he said. “They’re the most diverse group of vertebrates
in the world and even by that time had become a paradigm for ecology and
evolutionary studies.”
The forest immediately captivated Lister, a lecturer at Rensselaer
Polytechnic University in the US. “It was and still is the most
beautiful forest I have ever been in. It’s almost enchanted. There’s the
lush verdant forest and cascading waterfalls, and along the roadsides
there are carpets of multicoloured flowers. It’s a phantasmagoric
landscape.”
It was important to measure insect numbers, as these are the lizards’
main food, but at the time he thought nothing more of it. Returning to
the national park decades later, however, the difference was startling.
“One of the things I noticed in the forest was a lack of butterflies,”
he said. “They used to be all along the roadside, especially after the
rain stopped, hundreds upon hundreds of them. But we couldn’t see one
butterfly.”
Since Lister’s first visits to Luquillo, other scientists had predicted
that tropical insects, having evolved in a very stable climate, would be
much more sensitive to climate warming. “If you go a little bit past the
thermal optimum for tropical insects, their fitness just plummets,” he said.
As the data came in, the predictions were confirmed in startling
fashion. “The number of hot spells, temperatures above 29C, have
increased tremendously,” he said. “It went from zero in the 1970s up to
something like 44% of the days.” Factors important elsewhere in the
world, such as destruction of habitat and pesticide use, could not
explain the plummeting insect populations in Luquillo, which has long
been a protected area.
Data on other animals that feed on bugs backed up the findings. “The
frogs and birds had also declined simultaneously by about 50% to 65%,”
Lister said. The population of one dazzling green bird that eats almost
nothing but insects, the Puerto Rican tody, dropped by 90%.
Lister calls these impacts a “bottom-up trophic cascade”, in which the
knock-on effects of the insect collapse surge up through the food chain.
“I don’t think most people have a systems view of the natural world,” he
said. “But it’s all connected and when the invertebrates are declining
the entire food web is going to suffer and degrade. It is a system-wide
effect.”
To understand the global scale of an insect collapse that has so far
only been glimpsed, Lister says, there is an urgent need for much more
research in many more habitats. “More data, that is my mantra,” he said.
The problem is that there were very few studies of insect numbers in
past decades to serve as a baseline, but Lister is undeterred: “There’s
no time like the present to start asking what’s going on.”