The Endochory Story

February 2020
EndochoryDid you ever wonder why blackberries grow right along the trail? Endochory is the term used to describe when seeds are ingested (but not digested) by an animal and then pass the seeds through the intestines. Most of us learn that a good relationship takes maintenance. Plants and animals have formed some unique partnerships that ensure the benefits keep them coming back for more. The benefits can be very direct where the plants literally cater to the needs of the animals by wrapping edible fruit around tiny seeds. The animal gets a meal and the seeds get a free ride to a new destination; They are then deposited in a dollop of fertilizer and often in habitats where they are most likely to take root. In the case of the blackberry, sometimes right on the trail.
Plants have exploited, or rather, employed animals as seed dispersers because the animals are often paid for their service by wrapping or attaching nutritious and/or sweetened materials to the seeds. If the seeds are small enough it is most efficient to just swallow them whole and move on. Most of the fruits humans enjoy started from plants bearing tiny and often bitter fruits that are now unrecognizable from their ancestral parents. Through selective breeding we have produced unusually large and hyper-sweetened fruits that we now enjoy, including strawberries, figs, apples, bananas, and raspberries to name a few. As an employee, the animal then carries out its last task by carefully placing the seeds where they have their greatest chance for survival.
In many cases, to ensure the seeds arrive at the best quality habitat, the plant will target specific animal groups. For example, mammals have the ability to use the sense of smell to detect ripe fruits but most birds (except vultures) are not able to smell their food. If a plant is targeting mammals, the fruit may remain the same drab green color but soften and smell ripe. Without the ability to smell, a bird would need to check every fruit to learn which ones to eat, which they will do, but it takes time without the guarantee of success. If a plant wants the seeds to “fly” a bit farther, it may target birds by signaling ripeness with a change of color from green to bright red (like our native rose and Toyon). For example, the chili pequin peppers native to the southwestern U.S. and south into Latin America, advertise ripeness by turning bright red and add an extra kick to ensure it is specifically a bird that eats the fruit and not a mammal by using a spicy oil (Capsaicin) to burn the taste buds on the mammalian tongue (which most birds do not have).
But you do not have to look far for examples of these endochory relationships. We can turn to a common group of plants known as Mistletoe. The name is derived from its relationship with the birds seen eating the berries and where it grows. Apparently the word “Mistel” is the Anglo-Saxon term for “feces”, and “toe” can roughly be translated as “twig”, which gives us “feces-on-a-twig.” Birds that rely on mistletoe fruit to get through the winter, digest part but not all of the fleshy fruit, and excrete the seeds which retain a sticky coating that helps the seeds adhere to the branches in the exact location where it needs to grow.
As you walk along Putah Creek at this time of year you can still see bright red “hips” of our native rose (Rosa californica), “Christmas berry” Toyon (Heteromeles arbutifolia), possibly some remnant elderberry (Sambucus nigra) and maybe (mostly eaten by now) a few sweet dried raisins from our native grape (Vitis californica) all of which are beckoning to a hungry animal to have snack and then complete their seed “dooty” …possibly right on the trail.
Brian Keeley, Putah Creek Council Stewardship Program Manager
Rosa californica photo by Jerry Kirkhart