The Gardeners of the Forest

Elephants are the major gardeners of the rainforest. Weighing around 4000 kg, they are more than twice as large as the next biggest sympatric animal species (the one-horned rhinoceros) and four times as large as the third-place finisher (the gaur, Bos gaurus). Current taxonomy recognizes two extant species of elephant, the African elephant (Loxodonta africana), with forest and savannah subspecies, and the Asian elephant (Elephas maximus). They disperse massive amounts of seeds in conditions adequate for germination and establishment of tree seedlings, with estimates ranging between 300-2000 seeds/km2/day depending on elephant species and habitat. Recent studies indicate that seeds taken from elephant dung germinated as well or better than seeds from bovid dung or directly from fruit. Elephants were calculated to move seeds up to 10 times as far as domestic bovids. When elephants are missing, there are no ecological counterparts to compensate their absence.

The video from the Elephant Reintroduction Foundation nicely cartoons the type of mechanistic models that help us to estimate the ecological functions derived from mutualistic interactions between these megafrugivores and plants.
An empirical probability model estimated that the loss of elephants would result in reductions of about 66%, 42%, and 26% in the number of successfully dispersed seeds of key species such as Dillenia indica (chalta), Careya arborea (kumbhi), and Artocarpus chaplasha (lator), without compensation. In compensation scenarios, other frugivores could ameliorate reductions in dispersal, making them as low as 6% if species such as gaur (Bos gaurus) persist. Thus the importance of elephants as seed dispersers is amplified by the population reductions of other large disperser species throughout tropical Asia. The African and Asian elephants are the exclusive or near-exclusive disperser of a considerable number of plant species. The loss of forest elephants (and other large-bodied dispersers) may lead to a wave of recruitment failure among animal-dispersed tree species, and favor regeneration of the species-poor abiotically dispersed guild of trees.

– Beaune, D., Fruth, B., Bollache, L., Hohmann, G. & Bretagnolle, F. (2013). Doom of the elephant-dependent trees in a Congo tropical forest. Forest Ecology and Management, 295, 109–117.
– Blake, S., Deem, S.L., Mossimbo, E., Maisels, F. & Walsh, P. (2009) Forest elephants: tree planters of the Congo. Biotropica, 41, 459–468.
– Campos-Arceiz, A., & Blake, S. (2011). Megagardeners of the forest – the role of elephants in seed dispersal. Acta Oecologica, 37, 542-553.
– Sekar, N., Lee, C.L. & Sukumar, R. (2015). In the elephant’s seed shadow: the prospects of domestic bovids as replacement dispersers of three tropical Asian trees. Ecology, 96, 2093–2105.
– Sukumar, R. (2003). The living elephants: evolutionary ecology, behavior, and conservation. New York: Oxford Univ. Press.

Author: Pedro Jordano

Fazendo ciéncia e soltando pipa... I'm an evolutionary ecologist, working on how ecological interactions, e.g. mutualisms, shape complex ecological systems. Sevilla, España ·

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