Insect collapse in the Tropics points to climate change as the only factor warns Puerto Rican study.

I keep vigil.

Changes in temperature and weather patterns from a warming planet pose threats to millions of species (including humans) found in the tropics - that is because tropical species are thermally sensitive to changes in air temperature. The situation for the circle of life is dire as our fossil fuel addiction begins to kill off the base of the terrestrial food chain. 

Some tropical species might be able to move to colder climates as the earth continues to heat up, but most won’t be able to evolve in time putting tropical species at a higher risk of extinction than their counterparts in temperate regions. For example, in the Amazon, tropical trees are migrating upslope in the Andes to their extinction. Failure to migrate is of many factors that will cause the tropics to empty as the climate crisis intensifies. 

Also, a recent jaw-dropping study finds that in Puerto Rico's El Yunque National Forest found that ground insect populations had dropped 98% and in the canopy by 80 percent over just a 35-year time frame in the Caribbean island’s Luquillo rainforest. 

Bits of Science report on the newly discovered nightmare:

Climate news does not get worse: new field data show total insect (and other arthropod) biomass in Central American rainforest has declined 10 to 60 times since the 1970s. Meanwhile also insectivores, like lizards, frogs, and birds, are rapidly declining in the Luquillo rainforest of Puerto Rico. The driving force: climate warming.

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You probably recall last years shock study about rapid insect decline in North-West Europe. Inside German nature reserves flying insect populations declined by a staggering 76 percent in only 27 years, a German-Dutch research group wrote in PNAS.

Well, apparently, in the tropics the decline is even worse. At least in the tropical rainforests of Puerto Rice, two ecologists, Bradford Lister and Andres Garcia from Rensselaer Polytechnic University and Universidad Nacional Autónoma de México respectively conclude in the same journal.

There’s another big difference. The European insect decline study points in the direction of agriculture (insecticides) and other land use factors (habitat degradation, ecological inertia). In Puerto Rico, though the strongest driver of the insect decline is climate change – that’s at least what their statistical model shows as the only very likely cause, able to replicate the monitored sharp species declines.

And to be more specific: it’s temperature rise, the researchers add, not cyclones (from which the forest can thus far relatively quickly recover) or the El Niño/La Niña Southern Oscillation (ENSO). Droughts are locally more complex: while the Amazon rainforest is clearly drying out (from the South) the Central-American rainforests are more vulnerable to direct heat stress, but also increasingly to droughts.

The Guardian reports on the study:  Insect collapse: ‘We are destroying our life support systems’

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”.

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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%.

“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.”

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.

Katy Tur has been tackling the climate story lately and in the below video she interviews climatologist Michael Mann. 

Thanks for reading and caring. We have elections to win in 2020.