Plasticine caterpillars reveal a global pattern in predation

University of Alberta researchers contribute to a new global study that reveals predation hotspots

Julie Naylor - 18 May 2017

A new study has revealed a global pattern of predation on insect herbivores. It is well known that the tropics have many more species than the polar regions, and mountain valleys have more species than high summits. But now we know how ecological interactions among species, such as herbivory and predation, change across these latitudinal and elevational gradients.

Three University of Alberta biologists contributed to an international team of 40 researchers from 21 countries who made this discovery by examining predation rates of model plasticine caterpillars eaten along an 11,635 km gradient from the Arctic Circle to southern Australia, and from sea level to over 2000 m. What they found was that a caterpillar close to the poles has only one-eighth of the chance of being eaten compared to a caterpillar at the Equator, and that caterpillars living on mountain-tops were much less likely to be consumed.

"What was most fascinating was that the pattern was mirrored on both sides of the Equator and also across elevational gradients," says Tomas Roslin from the University of Helsinki in Finland, who led the analyses. "Moving up a mountain slope, you find the same decrease in predation risk as when moving towards the poles. This suggests a common driver could be controlling species interactions at a global scale."

The results were achieved with remarkably simple materials. To measure local predation rates, researchers glued thousands of caterpillars made from children's plasticine, a type of modeling clay, to common plant species. They left these "dummy caterpillars" exposed to predator attack, and revisited them several times to check for attack marks. The predators of caterpillars, such as birds, small mammals and ants, are tricked into thinking the model caterpillars the real thing, only realizing they have been deceived when they have taken a bite.

"By working together and using simple and easily replicated protocols, research teams from around the world can contribute to solving big global questions." -David Hik

University of Alberta's David Hik (Biological Sciences), and postdoctoral fellows Isabel Barrio and Erin Cameron contributed observations from experimental sites located in alpine tundra in the southwest Yukon and aspen parkland near Cooking Lake, Alberta, the only two Canadian sites in study. Predation rates at these sites fit the pattern observed globally suggesting that the role of predators in controlling invertebrate herbivores can be predicted over diverse landscapes, and predation can potentially limit the number of herbivores, even in more extreme environments.

Barrio and Hik have been studying factors influencing patterns of invertebrate herbivory in tundra environments for several years as part of the Herbivory Network, hosted by the University of Alberta. "These sorts of elegant, collaborative and distributed experiments make it possible to understand changes across continents. By working together and using simple and easily replicated protocols, research teams from around the world can contribute to solving big global questions", according to Hik. "We have been conducting similar types of distributed experiments in tundra environments, and we hope that this approach will also help us to better predict some of the potential impacts of rapid global warming in these environments."

The results were published in Science on May 18, 2017.