Amla And Friends – An Unlikely Investigation
Soumya Prasad shares fascinating insights about langur-chital interaction in amla seed dispersal in a riveting essay.
Photo: Soumya Prasad
On a late December evening in 2000, my field assistant Ramsaran and I sat near the Dhaulkhand Rao, nestled deep inside the Himalayan foothill forests of the Rajaji National Park. We pondered over the Indian gooseberry (amla) seeds we had noticed on the riverbed a month ago. We had spent weeks watching the amla trees trying to figure out who ate its fruit.
Amla fruits are collected by people living in the vicinity of forests to make pickles, shampoos and cosmetics. Other researchers have documented how this fruit supports forest-dependent livelihoods across India. There were also reports of declining amla populations from several locations, and concerns that this could affect the economic returns. Surprisingly, little research had been conducted on the animals that disperse the amla seeds as well as the ecology of the tree, information which is vital to our understanding of population declines in forests dependent on natural seed dispersal.
So far, we hadn’t seen a single bird feeding on the fruit. Macaques, civets and bears appeared disinterested as well. An occasional troop of langurs dropped by once or twice a month to spend the day clumsily feeding on fruits and leaves. A lot of fruits and branches fell as these heavy animals moved through the fragile branches of the amla tree. Often, after taking a bite or two, the langur would drop the remaining fruit. In winter months, chital would frequently follow langur troops and wait below the trees for the falling fruits and leaves. The large chital stags would bully the younger ones for the most rewarding spots. While we never saw langur swallow the fruit whole, the chital and barking deer appeared to do so. Despite spotting scopes and binoculars, the grass and leaf litter made it tough for us to be sure.
However, to establish fruit-eating by deer, we needed conclusive evidence. We marked fruiting branches and fallen fruit to record information on the rates at which the fruits were being removed by animals. Yet, after weeks of efforts, other than the fruits that bore langur-bite marks, we were unable to find evidence of fruits or seeds in faeces of deer or any other animal.
It was then that Dr. S. P. Goyal, my professor at the Wildlife Institute of India, lent us some camera traps. The first traps we set up were triggered by ‘pressure pads’. But this did not allow us to differentiate an animal visitor walking past the tree from one that actually fed on the fruit. That’s when Meherban, our field assistant, came up with a brilliant solution. We tied fruits to the camera trigger wire to obtain our first evidence for deer feeding on amla.
Photo: Raman Kumar
REVISITING THE STUDY
A few years later, I teamed up with the remarkable Dr. Andre Pittet from the electronics department of the Indian Institute of Science to develop a novel technique to quantify fruit-eating using camera traps. We programmed our cameras to take photographs every two minutes after animals triggered the camera-trap. On comparing the number of fruits remaining in the photos across this time-delay sequence (four photographs in eight minutes), we could tell fruit eaters from casual visitors. For the first time ever, our camera trap results allowed us to quantify the relative quantities of fruits consumed by different animals.
Done and dusted, we reached a conclusion – langur drop amla fruit, which are swallowed by deer. But do deer disperse these seeds as well? Earlier scientific work suggested that deer damaged larger seeds and were poor dispersers. Deer often disperse small grass and herbaceous seeds in their dung, but amla seeds were too large to come out in deer dung.
On the forest floor, we had been observing piles of cleaned out amla seeds, along with seeds of trees such as Terminalia chebula (harda), Terminalia bellirica (bahera) Ziziphus xylopyrus (ghoti) and Ziziphus mauritiana (ber). We suspected these were regurgitated by deer, but to prove the same, it would take us years. Deer are ruminating animals, with multi-chambered stomachs. The rumen, a large fore-stomach chamber is lined with bacteria, which break down fibres from grass and leaves. Due to a constraint on the size of particles that can move out of the rumen (~ 1 mm. for chital), larger particles are brought back into the mouth for re-chewing
(cud-chewing/ruminantion). Hard seeds of amla, ber, harda, ghoti and bahera resist being broken down during repeated mastication and are therefore regurgitated.
Photo: Soumya Prasad
SEARCHING FOR ANSWERS
To track this part of the amla’s story, I went on a two-year yatra across India to study chital in captivity. Across zoos and rescue centres, chital refused steadfastly to feed on amla, probably because they had never tasted any wild fruits!
In 2002, we found some chital in rescue centres in a remote village in the Western Ghats. These had been reared on kitchen scraps and wild fruit. Voila! These chital gave some amazing insights on seed dispersal by deer.
Amla was indeed regurgitated by deer as we had suspected all along. Chital expelled most of the fruit they fed on in shiny lots of seeds, devoid of pulp. These seeds spend between 10-40 hours in the rumen. As the chital move around in the forest, seeds get dispersed, away from parent trees and often at chital ‘bedding sites’. My colleague Sachin tracked the movement patterns of chital in Rajaji between 2013-16 to understand how the deer deposit seeds and consequently build forests.
The nutritional rewards provided by the amla tree to chital and langur undoubtedly ensure that the seeds get dispersed far and wide, which in turn ensures the survival of the plant. To address the benefits we humans derive (nutrition and economics), it is critical that we factor in the impact humans have on the deer-amla relationship.
Our ongoing work suggests that as long as we maintain patches of forest free from human harvests, deer will continue to provide vital dispersal services to the surrounding areas. Of course, there are several unanswered questions. In many forest areas, deer have declined or completely disappeared. Cattle and other domestic ruminants are poor replacements for the seed dispersal services compared to chital as domestic ruminants often rest in sheds. Consequently, dispersed seeds end up close to human habitation.
Photo: Soumya Prasad
Bottom line? The decline in amla populations and the associated economics can only be addressed by balancing the ecological relationships between humans with other species.
Author: Soumya Prasad, First published in: Sanctuary Asia, Vol. XXXVIII No. 6, June 2018.