The Secrets of Seed Dispersal: Hidden In Turtle Poop

This post was written by QBIC sophomore Emmanuel Medrano.

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Liu, Hong, Steven G. Platt, and Christopher K. Borg. "Seed Dispersal by the Florida Box Turtle (Terrapene carolina bauri) in Pine Rockland Forests of the Lower Florida Keys, United States." Oecologia 138.4 (2004): 539-46. 

For animals, it is easy to move between different locations. If they find themselves in an environment they do not like, they can simply migrate to other areas where they may be able to find more food or mates. As a result, populations of animals can occupy a great area of land. Plants, on the other hand, are incapable of this sort of dispersion. As they say, “the apple does not fall far from the tree”. However, plants are in luck, because animals can and do eat apples and other types of fruits. While in the stomach, the fruit becomes digested but the seed remains intact. This seed can then be excreted by the animal, and voila, the seed has moved.

            Seed dispersal is a very important mechanism because it helps plants cover more ground as well as grow in more favorable locations. Seed dispersal is often done by insects, birds, and many types of mammals. However, a study done by Dr. Hong Liu and her colleagues, investigated the role of turtles in dispersing seeds. In her study, Dr. Liu et al. (2004) examines what type of plants the Florida box turtle helps distribute, how the turtle’s digestive system helps the seed grow, and if the removal of fruit pulp plays a role in helping the seed grow.
            To start off, Dr. Liu and her colleagues searched for turtles with the help of a trained dog. After collecting them, the turtles were then placed into plastic buckets filled with 5cm of water (to stimulate bowel movements). The feces were then separated from then seeds by using a 2mm mesh. The seeds were examined to determine what species of plant they came from. This helped them identify what type of plants the box turtle helps by dispersing seeds. Thereafter, Dr. Liu and her colleagues planted the seeds into nursery pots. 

Photo from Wikipedia.

            Dr. Liu selected three species of plants based on how often they were found in the feces and the ease with which they could obtain seeds of these species from the actual plant. The purpose of this experiment was to see if passage through the turtle’s digestive system helped the seed grow. Her experiment wanted to see how many seeds grew (from the total obtained from the feces) and how fast they grew. She and her colleagues also perform a viability test on the seeds that did not grow. This test determined if the seeds could still grow later on and were simply dormant. Dr. Liu and her colleagues hypothesized that the turtle’s digestive system would help digest the fruit’s flesh and pulp, leaving only the seed. Leaving only the seed would then allow the seed to grow faster. To test this, they obtained and planted whole fruits (with the seeds inside), and seeds that had their pulp manually removed. This was done to see how often and how fast these seeds would grow (without passing through a turtle’s stomach).
            After performing various statistical tests, Dr. Liu and her colleagues compared the seeds from each species obtained from the turtle’s feces to the seeds obtained naturally and to those that had their pulp removed. From this, Dr. Liu found that the ability for the seed to grow after passing through a turtle’s stomach, was dependent on the species of plant the seed came from. Seeds from one of the species grew significantly faster and more often after passing through a turtle’s digestive system than seeds that did not. The opposite was true for the other two species they tested (seeds that had not passed through a turtle’s digestive system grew faster and more often). Dr. Liu attributed this variability to the fact that larger seeds are more likely to survive the inside of a turtle’s stomach, while small seeds would probably be digested. Dr. Liu then compared the seeds within the fruits to the seeds that had their pulp manually removed. From this, they found that removing the pulp helped the seeds of all three species grow more often than those still inside a fruit . They also found that removing the pulp only helped one of the three species grow much faster while the other two grew much slower than they would have if they still had the pulp.
            So can it be said that turtles do not play an important role in seed dispersal and that the seeds would be better off inside a fruit than inside a turtle’s stomach? The answer is no. Dr. Liu explains that even though some of the seeds did not grow, they still remained viable. This means that the seeds were simply dormant and could grow later on when conditions were optimal. Dr. Liu explains that the turtles may be preparing the seeds for growth by removing them from the fleshy fruit and the pulp. Dr. Liu’s study demonstrated that box turtles consume a wide variety of fleshy fruits from different plant species in the pine rockland forests of Florida. In the end these turtles help these plants by dispersing their seeds longer distances than the fruits would be able to travel by themselves. Growing in new areas helps these species compete more effectively and encounter more favorable conditions for growth such as better soil, more sunlight, less herbivores, and so on.