Why Are Scientists Gluing Fake Caterpillars?

May 31, 2017 By James H, Young Editor
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The world is filled with many diverse environments, each unique with its own ecosystem of living organisms.

From the lush green rainforests to the hot deserts, from the colorful deciduous forests to the white barren tundra -- the plants, animals and non-living things that comprise the ecosystem form a complex relationship and interact with each other. This relationship varies depending on the conditions of the environment like temperature, sunlight, water, fertility of soil, etc.

There is a lot more biodiversity (or more life) in a rainforest when compared to a tundra, but here’s a question: does the biodiversity of an area affect the likelihood of a prey being eaten? In other words, does a prey have the same chance of being consumed on both environments? A group of scientists conducted an experiment where they glued plastic caterpillars in natural habitats around the world. What did they find out?

What is Predation Risk?

Predation risk is the chance of being preyed upon, or the chance of a prey being caught and consumed by predators.

Predation risk plays an important role in how organisms, specifically prey, adapt and behave in order to survive. For example, a white-furred rabbit is more likely to be seen when against a green/brown environment, so its predation risk is pretty high. On the contrary, the same white-furred rabbit is not as likely to be seen in snow, lowering its predation risk.

Predation risk comes into play especially when foraging for food. Herbivores might want to find the best places for food in abundance -- it’s their best chance of survival, right? But, their respective predators might know that as well. If a predator knows that its prey will arrive at the food source, the predation risk increases as the prey is now more likely to be caught by the predator. So it is not always a good idea to go to the very best place for foraging; the oblivious prey just might be eaten instead.

The Study Results

Back to the testing of the plastic caterpillars. Caterpillars made of plasticine were glued onto leaves and other surfaces around the habitat.

When animals came to eat it, they left marks that tell the scientists what came by. Teeth marks mean a mammal tried to eat it, wedge-shaped marks mean a bird came by, and small piercings mean insects or arthropods tried to eat it. By doing this test all over the globe, scientists tracked down the predation rates in the habitats.

So what was the result? The caterpillars were eight times more likely to be eaten in habitats along the Equator than in habitats at the poles. In other words, caterpillars in a rainforest are  more likely to be eaten! But why? The habitats closer to the Equator house a lot more organisms, especially those belonging to the insect and arthropod family--  the biggest predator of these caterpillars.

In habitats closer to the poles, there are less of those predators, and since mammals and birds are not as likely to catch the caterpillars, there was less predation of the plastic worms. And this pattern occurs all throughout the world!

In the future, scientists are now planning to do the same thing, but with plants that prey consume!