If ever there was a mutually beneficial relationship, the arrangement between the pitcher plant and the shrew is one. The pitcher plant is a carnivorous plant with jug-shaped leaves forming a deep opening inside of which their digestive enzymes metabolize food. Most of the time, carnivorous plants eat insects (certain larger ones even eat small animals like mice and birds), but some, like the Nepenthes lowii pitcher plants dine on a particular delicacy.
In order to survive and grow, most plants need the basics: water, sunlight, air and nutrients. The top necessary nutrients are nitrogen, phosphorus and potassium. Nitrogen is considered the most important and plants absorb it more than any of the other elements.
Researchers studying N. lowii pitcher plants on the Southeast Asian island of Borneo found that the plants derived much of their nutrition from the feces of the tree shrew, a small mammal native to that mountainous, tropical forest region. Tree shews resemble squirrels, but are not rodents. They are slender animals with a long muzzle and sharp claws. Their diet includes insects, seeds and fruit. It turns out that shrew poop is rich in the much-needed nitrogen that the pitcher plant needs to thrive. Indeed, 57 to 100 percent of the nitrogen that the pitcher plant consumes comes from fecal matter.
It is very hard for carnivorous plants in mountain areas to find ants and other insects to eat, so the pitcher plants had to adapt. It is mainly the aerial pitcher plants that devour shrew feces. These pitcher plants are mature plants that attach themselves to vines to make it easier for the shrews to jump on (and poop in) them. The pitcher plant’s opening, also known as a pitfall trap, is suitably shaped for the shrew to place his bottom on in order to to eliminate waste. It is much like a toilet seat. When it rains, the water even washes the waste down into the funnel of the plant. Nature remembers to flush!
So, what does the shrew get in return for its precious poop? Well, the mountain tree shrew loves the nectar on the underside of pitcher plant’s leaves near the plant’s opening. While the shrew is licking the sugary treat, he is also efficiently positioned over the plant’s pit and is able to enjoy a meal and have a bowel movement without moving from his tropical toilet. It’s a “you scratch my back, I’ll scratch yours” type of business transaction.
Researchers believe this reciprocal relationship has been going on for a while. Besides clinging to vines to keep themselves above ground to give the shrew easy access to them, the pitcher plant also adapted in other ways to make its feces feast more available. Studies show the varieties of pitcher plants that are ground plants have slippery rims in order to trap insects. However, the aerial pitcher’s rim is not slick in order that the tree shrew can avoid falling off the plant during its meal and bathroom break. The N. lowii pitcher plants produce the most amount of nectar of any of their species and this keeps the abundant population of tree shrews happily fed. The plant is also sturdy enough to hold the small animal, which is usually not more than half a pound in weight.
The shrews also choose favorite plants to which they like to return for their dessert and dump. The researchers have videotaped evidence of this odd conduct that show the tree shrews rubbing the lids of their preferred plant with their genitals in order to leave their scent and stake their claim. They go back to the same plants repeatedly when it’s eating and pooping time.
This curious quid pro quo between the pitcher plant and the tree shrew gives a humorous, but strong example of the interdependent and interconnected nature of our world.