In a bid to determine how predation habits changed around the world, a team of scientists created and then dispersed almost 2,900 fake caterpillars across 31 different sites ranging from the Arctic Circle to Australia. The fake caterpillars were created with green plasticine, not uncommon to that used by children, and thanks to the material’s malleable properties, was able to show researchers if a predator had bit it.
Spread across 7,200 miles of latitude, six continents and from elevations ranging 0-2,100 meters, researchers placed the fake caterpillars on vegetation and regularly checked on them to record how many bite marks had been left. “But why caterpillars?” You may be asking yourself, well because they can be found everywhere, as the study’s lead author and Swedish University of Agricultural Sciences ecologist, Tomas Roslin explains:
“Geometer moths are among the largest families in the animal kingdom, with some 23,000 currently described species,” he says. “Anywhere you go, some of the local species will have green caterpillars.”
Praised as an innovative and ingenious way of tracking predation rates across the world using a relatively cheap and simple methodology, the study, published in Science, proved to be incredibly successful. The data gathered from the fake caterpillars led researchers to prove that predation was at its highest near the equator, with it lowering distinctly at the poles. For example, a caterpillar in Greenland incurred 87% less of a chance of being predated upon that its’ counterpart in Australia.
Additionally, the study showed that latitude wasn’t the only factor affecting predation rates, but that elevation also played a massive role. The numbers showed that the researchers’ little green companions were exposed to 9.6% less attacks per 100m increase in sea level.
Apart from confirming a long held belief that predation rates were higher where biodiversity was also high, scientists were able to make a discernible discovery that they aren’t entirely sure how to explain. Although predation rates did increase the closer you got to the equator, it was bugs that seemed to be more involved than their mammalian or aviary counterparts.
Why? Well, the current hypothesis inferred from this study is that birds and mammals are able to disperse themselves across a wider range when searching for food, whilst a bug’s size and properties made it more active in the equatorial regions and restricted its overall movement. Craig Benkman, an evolutionary ecologist at the University of Wyoming:
“Their data suggest that bird migration could be so effective that it equalizes predation rates on prey at a global scale,” says Benkman. “That is a remarkable result worth further testing, especially given the decline and vulnerability of so many migratory species.”
Scientists will need more time and a different study to be able to prove their hypothesis, potentially putting to use more of the fake caterpillars that were instrumental to the success of their first study. Stay tuned for more!