Elephants are irreplaceable seed dispersers

Elephants are irreplaceable seed dispersers

Subject: Environment

Section : Species in news

Context: Indian elephants are optimal seed dispersers of three large forest trees in West Bengal.

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• The dispersal of seeds far away from the parent tree maintains the high numbers of tree species in tropical forests. Trees depend on their fruit-eaters for seed dispersal, including elephants: the seeds of fruits they consume pass through their guts, come out undigested with dung and germinate when conditions are right.
• Using a combination of field data and theoretical modelling, scientists find that no herbivore can replace Indian elephants as the optimal seed dispersers of three large forest trees in West Bengal.
• 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).