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We all know poop. When it comes to plants, we might think of poop as the manure that gives our yards and crops a little pep and vigor. But poop is also one of the many ways plants propagate.
Plants need a little help getting their offspring out into the world. They’ve evolved many methods to do that, and providing a nutritional bit of food to a passing animal is one such way. It’s a delicate balance though: how to hide your young inside tasty fruits where they could possibly be crushed to death between jaws. That’s quite a gamble and some plants have evolved complex ways to ensure their seeds survive.
Here’s how it generally works. Those flowers we adore in spring often become fruits and berries we associate with summer and fall. When the seed (or seeds) inside are mature, the fruit becomes ripe. Often, the fruit takes on a distinctive color and odor to encourage animals to eat up. The seeds are either discarded when the fruit surrounding it is consumed, or they pass through the animal’s digestive tract. When the animal poops, it passes the seeds away from the parent plant in new areas which allows the plant to colonize new territory. Germinating away from the parent plant also reduces competition for resources like water and soil nutrients, and minimizes spread of diseases between plants that would otherwise be growing too close to one another. The seed also gets an added boost of fertilizer and moisture in the animal waste.
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| Cassowary bird. (Photo: Summerdrought- Creative Commons Attribution-Share Alike 4.0 International |
To weather this challenging journey inside a digestive tract, seeds must have a really strong form of protection like a coating, but not so strong so as the plant cannot germinate. For some plants, their seeds actually go through two digestive tracts which assists with softening that hard shell. This happens when a predator eats another animal that has eaten seeds, as with certain birds of prey that eat seed-eating lizards.
Some plants have evolved so they can only propagate by passing through an animal’s digestive tract. One example is with the cassowary plum (Cerbera floribunda). The fruit of this plant is poisonous to most animals and humans, but not to the cassowary bird of Australia. The bird’s stomach contains a unique combination of enzymes that allow it to digest the fruit while leaving the seed intact.
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| Coyotes at BFL. |
Like with just about everything in the natural world, climate change is altering normal patterns of seed dispersal through poop. Coming into play is an animal we don’t often associate directly with the process: carnivores. Predators often travel longer distances in comparison to their fruit-eating prey. As more habitat becomes degraded and animals must relocate, these predators carrying seed-eating prey in their bellies will be key to dispersing seeds in new territory.
Seed dispersal through poop can be seen in action at one of our own field labs, Brackenridge Field Lab. The examples are plentiful, but one interesting plant is the Japanese raisin. The stem is edible and the fruits are considered a hangover reducer. Recovering from a bender is probably not the reason why coyotes eat it, but their consumption assisted the spread of this plant through the field lab.
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| Photos: Larry Gilbert. |
"Chory-WHAT?"Some cool new words to use at your next Zoom happy hour.Zoochory: dispersal of seeds by animals. Endozoochory: seed dispersal by ingestion by animals. Allochory: a passive seed dispersal where a vector or secondary agent is used to disperse seeds. These vectors may include wind, water, animals or others. Autochory: is the process of fruit and seeds dispersal by means of some kind of physical expulsion, often explosively. The fruit explodes, shooting its seeds some distance to the ground surrounding the parent plant. Autochory is also called discharge dispersal. Diploendozoochory: the transportation of seeds inside two animals at once. Like when a predator has eaten an animal that has eaten a fruit with seeds. Think: Russian nesting dolls. |
SOURCES:
Avis-Riordan, Katie. “How plants hitchhike on animal poo.” Royal Botanic Gardens Kew. April 1, 2020. (https://www.kew.org/read-and-watch/plant-seed-dispersal-animal-poo)
Snowdon, Wallis. “Scat Secrets: Edmonton study explores role of predator poop in spreading plant seeds.” CBC News. Feb 23, 2017. (https://www.cbc.ca/news/canada/edmonton/university-alberta-animal-scat-study-prey-predator-seeds-1.3996489)
“Seven things You (Probably) Didn’t Know About the Cassowary” Rainforest Trust, September 22, 2017 (https://www.rainforesttrust.org/seven-things-probably-dont-know-cassowary/)
