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Two pitcher plants side by side.
This carnivorous plant has turned itself into a toilet.
Image: Alastair Robinson

Carnivorous plants eat insects, but what to do if there are not many insects about? Answer: find a new form of food!

Nepenthes, the tropical pitcher plant, is known for its long colourful pitcher. It entices insects to its nectar-covered lid, where they lose their footing. Then they slip and slide down into the pitcher to be drowned in the enzyme fluid below. Yum, breakfast! Pitcher plants live in poor soils, so they need the extra nutrients from their prey to survive.

But several sub species of pitcher plant (N.lowii and N.rajah) live high in the mountain summits of Borneo where insects are few and far between. To survive, they have adapted to take advantage of a different fertilizer: shrew poo! And not just shrew poo but rat scat as well.

Small mammal feeding from pitcher plant and leaving fertilizer for the plant.
This rat is taking a night-time toilet break!
Image: Greenwood, M., C. Clarke, C.C. Lee, A. Gunsalam & R.H. Clarke 2011.

Over time, these pitcher plants have broadened their funnel openings and pushed back their lids. The changes encourage little mountain mammals to sit across the pitcher whilst feeding on nectar and leave their poop, almost like a high-rise toilet.

Scientists first discovered this relationship over 10 years ago, but there’s still plenty to learn. Dr Alastair Robinson from Royal Botanic Gardens Victoria and his colleagues have been studying pitcher plants to see whether poo makes a good snack for a plant.

“We found that nitrogen capture is more than two times greater in species that capture mammal droppings than in other Nepenthes,” says Alastair. So compared to their carnivorous cousins, our poo pitchers are capturing way more nutrients.

Turns out in Borneo’s tough mountainous environment, poop eating plants is the way to grow!

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