EPOW Ecology Picture of the Week -- Fruit of the Elephant

Explanation: This stately tree of the Congo Basin of tropical central Africa has quite a story to tell.

The fruit is simply enormous and grows directly from the trunk -- a condition in botany known as being sessile, or a fruit that is attached directly by the base and not by a stalk. The fruit is known as the bellybutton fruit because -- well, look at the photo and you tell me. The tree is known by its local French name as arbre à mamelles which transliterates to "tree with udders."

We discovered this tree growing along an elephant trail during a trek into the remote Salonga National Park in the Congo Basin. This was quite auspicious.

Apparently, only elephants can eat this tree's fruit after it has fallen to the forest floor. The elephants pierce the tough husk of the fruit with their tusks. The elephants then disperse the fruit seeds throughout the jungle -- mostly along their traditional movement pathways. When dispersing them in their dung, they provide a rich fertilizer ... and do so mostly along their trails. The seeds then germinate and grow well along the open travel lane where there is more sunlight than under the adjacent dense forest floor.

Over many generations, the forest elephants of the Congo have developed a network of pathways and trails that connect many of these, and other, fruit trees ... and the trails are lined with their defecation and the growth of the dispersed tree seeds.

Apparently, this tree -- perhaps just one tree species among at least two dozen -- seems dependent on the forest elephant for its dispersal, in the same way that the Trewia tree of northern India is dependent on the great Indian one-horned rhinoceros for its dispersal. This is a wonderful example of functional convergence, where two large but unrelated ungulate species -- the elephant and the rhino -- in completely different ecosystems and continents -- Africa and India -- have evolved a very similar ecological functional role and symbiotic relationship with a tree!

Moreover, as with the rhinos of India, the forest elephants of the Congo create and maintain travel pathways that are used secondarily by a variety of other forest creatures, such as wild boar, forest hogs, duiker and other antelopes, and even ecologists on expedition...

In this way, elephant, tree, forest, and ecosystem are united in amazing ecological relations that we are just starting to unravel.

Information:
    Feer, F. 1995. Morphology of fruits dispersed by African forest elephants. African Journal of Ecology 33(3):279-284.
     Hawthorne, W. D. and M. P. E. Parren. 2000. How important are forest elephants to the survival of woody plant species in Upper Guinean forests? Journal of Tropical Ecology 16:133-150.

EPOW - Ecology Picture of the Week