Crocodylians Eat Fruit but may not Disperse the Seeds

Scientists know some species of mammals, birds, turtles, and lizards eat fruit and disperse the still viable seeds across the landscape in their scat.  Surprisingly, 13 of the 18 species of crocodylians in the world are known to actively seek and eat fruit also, yet until recently scientists didn’t know whether the seeds they defecated were still viable or not.  Adam Rosenblatt, formerly of Florida International but currently on the Yale faculty, led the first ever study of fruit seed viability in crocodylian crap.  He analyzed the contents of 54 American alligator stomachs from specimens living in the Everglades.  He found fruit seeds in 12 of them.  His alligators ate the fruit of red mangrove, coco plum, and pond apple, but the latter, a type of pawpaw, was by far the most common fruit found in alligator stomachs.  One specimen had 1286 pond apple seeds in its stomach.  Each pond apple has about 6 seeds, so that means this particular alligator ate at least 200 pond apples.

The scientists planted 20 pond apple seeds recovered from alligator stomachs, resulting in a 0% germination rate vs. a 75% germination rate for pond apple seeds that did not go through an alligator’s digestive system.    Alligators often scavenge well-rotted carcasses infected with toxic bacteria, but their strong digestive acids destroy the toxins.  Dr. Rosenblatt belives these strong digestive acids also destroy the viability of pond apple seeds.  Moreover, alligators have a slow metabolic rate, and the seeds can stay in an alligator’s digestive system for months.  Pond apples germinate rapidly and lose viability if not exposed to soil within a short period of time.  Dr. Rosenblatt doesn’t know if the same holds true for other species of fruit and other species of crocodylians, but it appears that American alligators do not help disperse pond apples.

gator fig. 2

Alligator actively seeking out kumquats.

Pond apple (Anona glabra).  Scientists planted pond apple seeds they recovered from alligator stomachs.  None of them germinated compared to the average 75% germination rate of non-digested pond apple seeds.

Pond apples have been introduced to Australia where they have become an invasive species.  Apparently, the native cassowary and feral pigs are facilitating the spread of this species on that continent.  Cassowaries and hogs have quicker digestive systems and weaker stomach acids than those of alligators, and pond apple seeds are capable of surviving the journey through the alimentary canals of these 2 species.  Pond apple seeds are frequently found sprouting in the fresh cassowary and hog dung.

Cassowary and young.  The seeds from pond apples eaten by cassowaries are viable, and this bird is helping spread this invasive species in Australia.

Reference

Rosenblatt, Adam; and Scotty Zara, Michael Heithore, and Frank Mazzetti

“Are Seeds Carried by Crocodylians Viable? A Test of Crocodilian Suochory Hypothesis”

Southeastern Naturalist 13 (3) 2014

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