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Jumping SpiderAccording to a new study, invertebrate populations have declined by 45 percent while the human population has doubled.

The study, led by UCL, Stanford and UCSB, focuses on the human impact on invertebrate species (spineless creatures such as insects, arachnids, crustaceans, slugs and worms). It is unique in the sense that most human impact studies focus on vertebrate populations – specifically land-dwelling ones. As the authors note, the human impact on terrestrial vertebrates has been the extinction of 322 species since 1500.

The loss of larger, more visible species has been documented throughout history and resulted in varying environmental fallout. But the decline of insects – less visible and seemingly less consequential – has the potential to cause global disruptions in food supplies.

The study, published in the journal Science, states that insect pollination is necessary for 75 percent of the planet’s crops. Insects also contribute to the health of those crops; in the U.S. alone, pest-killing insects save the agricultural sector an estimated $4.5 billion per year. Invertebrates also aid in nutrient cycling and decomposition, transferring seeds from one place to another.

Researchers discovered that, while vertebrate populations have declined by 25 percent on average, the rate of invertebrate decline was nearly double that. Of species monitored, 45 percent were in decline due to habitat destruction and climate change. In the UK, common insect populations decreased between 30-60 percent over a 40 year period.

Dr. Ben Collen of UCL Biosciences said that he and his colleagues were “shocked” by these numbers. Scientists assumed invertebrates were much more resilient.

Professor Rodolfo Dirzo, the lead author of the study, warns that the decrease in insects will lead to higher rates of disease:

“Where human density is high, you get high rates of defaunation, high incidence of rodents, and thus high levels of pathogens, which increases the risks of disease transmission. Who would have thought that just defaunation would have all these dramatic consequences, but it can be a vicious circle.”

The problem is not so much extinction, he says, but the “loss of critical ecosystem functioning.” This loss will become much more obvious over time, though how to restore it remains to be seen.

To read the full report, Defaunation in the Anthropocene, click here.

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