New Delhi: Asian elephants play a vital role in the ecology of the forest and help spread green cover because of their eating and movement pattern, says a study by the researchers of the Indian Institute of Science and Princeton University.
The researchers studied the eating and movement pattern of the domestic cattle, buffaloes and pachyderms as they are the ones who often venture inside the core of the forest and also travel a significant distance daily. More importantly, these species are herbivores.
They also chose the Buxa Tiger Reserve for their research. The core area of the reserve consists of native vegetation, surrounded by areas consisting of plantations and degraded forest tracts.
According to a 2003 estimate, there are 217 elephants in Buxa.
In the study conducted by Nitin Sekar and Chia-Lo Lee from Princeton University and Prof Raman Sukumar from the IISc over three fruiting seasons (2010-2012), the researchers chose three species of plants for their study: Dillenia indica (the elephant apple), Artocarpus chaplasha (the chaplash) and Careya arborea (wild guava). These are mostly eaten by the cattle, buffaloes and elephants.
"It is well known that elephants can swallow very large seeds and excrete them undigested. Sometimes, seeds that pass through the elephant gut germinate better than those that are taken directly from the tree. Elephants are also able to disperse seeds far and wide due to the fact that they tend to cover several kms every day," the research paper said.
In the fruit trees chosen by the researchers, they found that the elephant apple produces relatively hard fruit that are about 430 gm in weight. Because the hardness of the elephant-apple fruit, it makes pachyderms its predominant consumer. Chaplasha and wild guava trees produce softer fruits, which are easy for smaller fruit-eating species to handle.
The researchers conducted several feeding trials in order to observe how much of each species of fruit passed through each of the three animals' (cattle, buffaloes and elephants) guts, as well as the time spent in the gut. Following this, they assessed the germination rate of seeds that had passed through each of the species' guts.
The domestic cattle retained seeds in their guts for longer periods than elephants did, and elephants excreted far more seeds than cattle. Elephants constantly excreted seeds that germinated as well (if not better) as those that were taken directly from the plant, while this varied in cattle. This was especially noticeable in the case of the elephant apple fruit.
Another part of the study involved tracking the movement of domestic cattle and elephants to see how far they dispersed the seeds.
When they looked at data from GPS collared elephants, they saw that the animals sometimes moved over 50 km in a span of a 100 hours. Similarly, bovid herds were followed through the day, until they settled for the night. The cattle did not move farther than 5 km from their point of origin.
They concluded that elephants were capable of dispersing seeds much farther than domestic cattle and were better dispersers of these seeds when compared to domestic bovids not only in terms of movement, but also because more seeds survive the elephant gut, especially in the case of Dillenia indica. Cattle make for moderately effective dispersers, but cannot achieve the results elephants can.
"I didn't really have strong expectations, actually. If pressed, I guess I can say that I was struck by how few seeds survived gut passage in cattle, especially for elephant fruit, which has such small seeds.
"I was also surprised that the bovids tended to go in the same direction every day when they were grazing and browsing, even though they were usually unsupervised and could go wherever they wanted. That of course made them less likely to disperse seeds very far. I still don't understand why they behave that way," Sekar said.