The progressivedisappearance of large seed-dispersing mammals, such as elephants and rhinos, endangers the structural integrity and biodiversity of the tropical forests of Southeast Asia. An international team of researchers, with Spanish participation, confirms that not even other herbivores such as tapirs can replace them.
“Themegaherbivores are “gardeners” of the humid tropical forests: they favor the regeneration of the forest and maintain its structure and biodiversity “, Ahimsa Campos-Arceiz, lead author of a study published in Biotropica and researcher at the School of Geography of the University of Nottingham in Malaysia, explains to the SINC agency. In these forests of East Asia, the great diversity of plant species prevents there is enough space for all the trees to germinate and grow.In addition to the low light, the dispersal of seeds is complicated by the absence of wind as they are trees of up to 90 meters high Vegetation is therefore limited to dispersal by animals that consume the pulp and spread the seed by dropping it, regurgitating it or defecating it after a few hours.
In the case of large seeds, “the plant needs a large animal that is capable of eating, transporting and defecating the seeds in good conditions”, according to Luis Santamaría, co-author and researcher at the Mediterranean Institute for Advanced Studies (IMEDEA) of the CSIC . This is where elephants and rhinos come into play, which digest food poorly and disperse large amounts of seeds over great distances due to their slow digestion.
However, habitat loss, man-elephant conflict and poaching havereduced by 95% the historical range of distribution of the Asian elephant ( Elephas maximus ), and have left rhinos one step from extinction:less than 50 individuals remain of the Javan rhinoceros ( Rhinoceros sonicus ) and 200 of the Sumatran rhinoceros (Dicerorhinus sumatrensis ). According to the red list of the International Union for Conservation of Nature (IUCN), elephants are in “danger of extinction” and the two species of rhinoceros are “critically endangered”.
Faced with this situation, the research team evaluated the capacity as a seed disperser of another large herbivore weighing 300 kg, which for cultural reasons is not hunted and which has a digestive system similar to that of elephants and rhinos: the Asian tapir (Tapirus indicus). The study allowed us to analyze the effect of tapir dispersal on the survival of seeds from nine different plants, including some large ones, such as mangoes and durians, and other smaller ones, such as the “elephant apple” (Dillenia indica). The results show, among others, that tapirs defecated 8% of the 224 tamarind seeds ingested (of which none germinated), compared to 75% of the 2,390 seeds ingested by the elephant (of which 65% germinated). . In short, they are not good dispersers for plants with large fruits and seeds.
According to the authors, if megaherbivores disappear from the ecosystem, their contribution to ecological processes will be lost and the ecological trajectories of the ecosystem will change irreversibly, so that “the most likely consequences would be the change in the structure of the forest and understory, and the loss of certain species “.Elephants and rhinos have unique ecological functions and cannot be substituted by other species. In this sense, species that depend on large animals will become increasingly rare, while those that depend on the wind or smaller and more abundant animals will increase in density and importance.
To avoid this scenario, the researchers suggest protecting megafauna, and in some cases reintroducing previously disappeared megaherbivore species.
