Friend or foe? The way bats disperse seeds benefit farmers: Study

Fruit bats perceived to be more beneficial due to clumped seed dispersal of commercially important crops such as cashew and areca

Breeding season of Indian Flying Foxes (large fruit bats that we regularly encounter) corresponds with the cashew fruiting season in peak summer | Photo Credit: FILE PHOTO

The way bats disperse seeds needs to be sustained as an important ecosystem service despite some latent zoonotic risk, said a study that focused on human-bat interactions in five agroforestry landscapes along India’s Western Ghats for selected commercial fruit crops such as cashew, areca, banana and other fleshy fruits. The researchers explored the connection between seed dispersal by bats, how people perceived and tracked bat seed dispersal for economic value generation, and potential socio-ecological pathways for disease risk.

Their paper, ‘Forbidden fruits? Ecosystem services from seed dispersal by fruit bats in the context of latent zoonotic risk,’ was published in the peer reviewed journal Oikos. The researchers, Kadambari Deshpande, Abi T. Vanak, M. Soubadra Devy and Jagdish Krishnaswamy (now at the Indian Institute for Human Settlements) are from the Ashoka Trust for Research in Ecology and the Environment (ATREE).

Speaking to The Hindu, Ms. Deshpande said bats have mostly been portrayed and perceived negatively. Apart from coming across some “positive, interesting and new narratives” in Kerala, the Nipah virus outbreak in that State in 2018 was another factor that triggered them to include an analysis of likely disease risk in the study.

“We found that people tracked bat-dispersed seeds and collected them for use, realising significant economic value from the process. Overall, fruit bats were perceived to be more beneficial due to clumped seed dispersal of commercially important crops such as cashew and areca, than harmful due to damage or loss to pulpy fruits like banana or guava. We found that areas where perceptions of benefits from bats were high were areas with lower likelihood of zoonotic risk,” she explained.

Bats helped reduce labour costs

As bats aggregated seeds or nuts of valuable cash crops such as cashew and areca, it helped in reduction of labour costs. Even the pulpy fruits, if harvested early when still unripe, would also not incur losses, as bats ate mostly ripened fruits. If farmers acted in a timely manner to harvest fruits, they could also avoid most fruit damage by bats, she explained.

In terms of disease risks, they detected an overall negative correlation between social perceptions about bats and potential disease risks. This means that in areas where people reported greater benefits from bats, risks were lower.

Highest for cashew

The study also found that the extent of bat-mediated clump-dispersal was highest for cashew, especially in isolated plantations. Expanding on this, Ms. Deshpande said on the one hand, bats benefit cashew-associated people significantly by dispersing cashews in clumps near plantations. On the other hand, it is likely that disease risk might be associated particularly with cashew plantations as bats love cashew-apples because of the juicy pulp, strong scent, and fruit position away from foliage that makes them easy to detect and pluck. Compared to other fleshy fruits that are generally harvested unripe, cashew-apples are generally left on trees till they ripen, increasing the chance of bat visitations.

“Subsequently, human contact with bat-eaten cashew-apples increases at the time of seed collection and handling of bat-bitten fruits, which may have bat secretions on fruit surfaces. Breeding season of Indian Flying Foxes (large fruit bats that we regularly encounter) corresponds with the cashew fruiting season in peak summer. Breeding females are under higher stress, which can increase the risk of viral transmission onto fruits and thereby to people,” she said, adding that many such factors might lead to contact pathways between bats and people, which could likely increase risks too.

Since COVID-19, has there been any change in the perception towards bats? There is more awareness about the existence of bats in our surroundings since the pandemic began, but people still need to read through the news about bats with more discretion, they say. “Among the rural and peri-urban residents, perceptions and attitudes towards bats have not changed drastically from largely positive to negative, which is an encouraging sign. Human-bat relationships really need to be brought to the fore, not just for more awareness, but also to spread the right kind of knowledge and caution to be exercised, to maximise benefits from bats while minimising potential risks,” Ms. Deshpande concluded.