News reports have come out about Asian Elephants (Elephas maximus) being crucial to the dispersal of the seeds of three different species of plants – the Chaplash Tree (Artocarpus chaplasha), the Slow Match Tree (Careya arborea) and last but not the least, the Elephant Apple (Dillenia indica). Studies indicate that like their distant cousins, the African Forest Elephants (Loxodonta cyclotis), the Asian Elephants help spread the seeds of forest trees more effectively than any other species of herbivore (like wild and domestic bovids). Biologists have discovered that megaherbivores like Elephants improve the chances of successful germination in fruit-bearing plants by a significant percentage.
The consumption of wild fruit and the passage of the seeds within, through their digestive tract, boosts the survival rate of seedlings. Scientists also found that Elephants can spread seeds over far greater distances than other frugivores (like monkeys and rodents). Some African Forest Elephants were found scattering seeds over a distance of more than 50 km in the Central African Rainforests. While this is further proof of the beauty and intricacy of the web of life, it also raises troubling questions. How are plants like the Chaplash Tree, the Slow Match Tree and, the Elephant Apple going to fare in forests where Asian Elephants no longer flourish?
This is what ‘The Hindu’ newspaper published in its article, ‘Elephants are Irreplaceable Seed Dispersers’, (by Aathira Perinchery, dated January 6, 2018):
Scientists at Bengaluru’s Indian Institute of Sciences and Princeton University, USA, quantified the role of Indian elephants and other herbivores (including Indian gaur, cattle, monkeys and wild squirrels) in dispersing the seeds of three tree species – the elephant apple tree (Dillenia indica), the slow match tree (Careya arborea) and chaplash, a jackfruit tree endemic to north-eastern India (Artocarpus chaplasha) – in Buxa Tiger Reserve, West Bengal.
The team collated previous field data, including camera-trapping and watching fruiting trees to see what fruits and how many each herbivore ate, counting seeds in dung and testing how many germinated. Using this and available data from literature, they quantified aspects of seed dispersal such as the time that seeds spent in animals’ guts, the distance that the seed was dispersed and natural processes that killed dispersed seeds.
Incorporating these into a probability-based model, the team’s study published in Conservation Biology found that without elephants, the number of seeds that survived after dispersal decreased to between 26% and 72% for each of the three tree species if other animals fail to compensate for the elephants. Though compensatory fruit removal by other animals negated this pattern, seed dispersal distance still declined by 30% for elephant apple and 90% for chaplash. Elephants dispersed seeds between 40 and 50 km, far higher than gaur (10 km) and cattle and buffaloes (5 km).
The following is an excerpt from the Scientific American’s article ‘Asian Elephants Help Seed the Forest’ (by John R Platt, dated November 11, 2016):
Researchers from University of Hohenheim in Germany and other institutions tested this out with a fruit highly associated with elephants: the chulta, or elephant apple (Dillenia indica), an economically important fruiting tree native to Southeast Asia. A trial conducted in Thailand involved feeding the apples to six female elephants, all of which were rescued from previous lives as street beggars. The researchers then followed the elephants, tracked how many hours it took for the apples to be defecated out, and collected the dung and used a sieve to retrieve the apples’ tiny seeds.
After that monumental task they planted 1,200 elephant apple seeds, including some control seeds chopped directly out of the fruit, and found that those which had been consumed and partially digested by pachyderms had the highest germination success rates. The more time before the seeds were pooped out, the better they did. The digested seeds also germinated faster than those which had not first gone through an elephant’s gut. This, the authors wrote, is important because once the seeds are on the ground they can be eaten by other predators. The faster the seeds sprout, the more likely they are to survive.
The studies just go to show how the loss of even one species could tilt the balance of entire ecosystems and endanger the prospects of those which are dependent on them. Something similar is happening to Balanites wilsoniana, a species of tree found in Central and Western Africa. The declining numbers of African Bush Elephants (Loxodonta africana) is endangering the future of the tree in countries like Uganda. Something similar should have wiped out the Avocado (Persea americana) of Central America. Fortunately, the species hung on, thanks to human beings arriving in the New World and taking over the role of the native megafauna they had wiped out (Giant Ground Sloths, Gomphotheres and Mammoths). What lies in store for the Elephant Apple?
Image Attribution: The image above, sourced from Wikimedia Commons, is a photograph of the fruits and foliage of the Elephant Apple. It was uploaded by Primejyothi.
- ‘Elephants are Irreplaceable Seed Dispersers’, (by Aathira Perinchery, dated January 6, 2018), The Hindu
- ‘Asian Elephants Help Seed the Forest’ (by John R Platt, dated November 11, 2016), Scientific American
- ‘Elephants: the Gardeners of Asia’s and Africa’s forests’ (by Jeremy Hance, dated April 25, 2011), Mongabay
- ‘On the Importance of Elephant Poop’ (by Sarah Zielinski, dated July 28, 2015), Science News
- ‘Why the Avocado Should Have Gone the Way of the Dodo’ (by K Annabelle Smith, dated October 24, 2013), Smithsonian.com