- A recent study found significantly higher caterpillar predation in Kerala’s sacred groves than in nearby multi-storied home gardens, indicating these small forest patches help sustain predator-prey interactions.
- While predation declined with increasing distance from the Western Ghats within sacred groves, their size did not explain the interactions, suggesting habitat complexity can buffer the effects of fragmentation.
- The findings suggest that culturally protected forest fragments help preserve ecological functions and support ecosystem services in human-dominated landscapes, complementing larger protected forests.
Scattered across India, sacred groves are often celebrated as relics of ancient forests. Protected for generations through cultural and religious traditions, these patches of native vegetation often serve as refuges for native plants, birds and insects. Now, a new study finds that instances of predators eating caterpillars was consistently higher in Kerala’s sacred groves than in nearby multi-storied home gardens, indicating that this ecological process that helps regulate populations of herbivorous insects, was stronger in sacred groves.
“Predation is a fundamental ecological process that shapes community structure and ecosystem functioning,” says Gopika Viswan, a researcher at the Ecology Lab, Central University of Kerala and the study’s co-author, adding that “Changes in predation can trigger strong ecological consequences, including trophic cascades and altered ecosystem stability.”
“Species richness or abundance studies capture only the structure of ecosystems, not how they function. Ecosystems are sustained not merely by the presence of species, but by interactions among them, such as prey-predator interactions,” she explains.
Testing fragmentation
The study was conducted in the northern Malabar region of Kerala’s Kasaragod district, where at least 117 sacred groves are scattered across a mosaic of agricultural areas and home gardens, stretching from the Western Ghats to the Arabian Sea.
Researchers selected 12 sites located between 8 kilometres and 44 km from the Western Ghats. At each site, they paired one sacred grove with one multi-storied home garden close by, located 1-2 km apart, to compare predator-prey interactions across habitats and varying levels of isolation from the biodiversity hotspot. Fieldwork was carried out during January and February in 2024 and 2025, as these months coincide with the peak activity of insectivorous birds and the region.
“The sacred groves and home gardens represent contrasting habitat types embedded within human-dominated landscapes, yet both occur at varying distances from the Western Ghats, which acts as a source pool for species,” says says Palatty Allesh Sinu, associate professor at the Ecology Lab, Central University of Kerala, and the corresponding author. “Sacred groves particularly are islets of forest patches. This allowed us to test some aspects of the theory of island biogeography, especially the effect of distance.”
To measure predation, the researchers deployed 1,296 artificial caterpillars, made from non-toxic, non-hardening, non-drying plasticine across the two habitats. Plasticine caterpillars are widely used in ecological studies because predators leave distinctive bite marks on the soft models, allowing researchers to identify the broad groups responsible for the attacks without directly observing predation. Green and reddish-brown artificial caterpillars, representing the most common caterpillar colours observed at the sites, were placed on leaves, branches and stems of trees and retrieved after 48 hours.
During the second year, the team also deployed 864 freeze-killed mealworms wrapped in a synthetic adhesive, leaving their heads and tails exposed to attract predators and help identify the insects involved. The researchers analysed the data using generalised linear mixed-effects models to test how habitat type, distance from the Western Ghats, caterpillar colour and where the caterpillars were placed influenced predation while accounting for differences among sites and years.
Small forests, big ecological role
Overall, predation rates were significantly higher in sacred groves than in home gardens. Arthropods, particularly ants, were the dominant predators, accounting for about half the attacks (57-61%), while birds were the second most important predator group, contributing 22-35%. The study also found that green caterpillars were attacked less frequently than brown ones, largely because arthropods preyed on them less often. Caterpillars were placed on leaves, branches and stems in both sacred groves and home gardens, and overall predation was lower on leaves than on branches or stems.
Some of the findings challenged the researchers’ expectations. “One of the most surprising outcomes was that predation did not follow a simple, uniform decline with increasing distance from the Western Ghats, as would be expected under classic fragmentation theory. We initially anticipated that increasing isolation from this biodiversity source would reduce predator activity across both habitats. While this expectation held true within sacred groves where predation declined with distance, it was contradicted in home gardens, where both overall and bird predation actually increased,” says Sinu.
The contrasting responses suggest that the ecological effects of fragmentation can depend strongly on habitat type rather than following a universal pattern. The researchers also found that grove size did not explain the observed patterns, indicating that habitat quality and structural complexity, rather than patch size alone, were driving predator activity.
The study also recorded relatively high levels of bird predation compared with many previous tropical studies. According to Viswan, the relatively large size of the artificial caterpillars used in the experiment, coupled with the region’s diverse community of insectivorous birds, likely contributed to the stronger avian predation observed.
Consistently high predation was observed within sacred groves despite their small size and isolation. “The strength and consistency of this effect emphasised the disproportionate ecological importance of even small forest remnants. Sacred groves, despite being isolated and limited in size, maintained high levels of predation across all major predator guilds — arthropods, birds and small mammals — demonstrating that habitat complexity can buffer the negative effects of fragmentation,” says another co-author Bhavya Lakshmi, a researcher at the Ecology Lab, Central University of Kerala.
The findings reinforce the importance of conserving small forest patches. “The broader implication of our study is that conservation in fragmented landscapes cannot rely solely on the protection of large, continuous forests. Small, culturally conserved forest patches such as sacred groves can maintain ecological functions and provide ecosystem services even when isolated within human-dominated landscapes,” says Sinu.
Banner image: A sacred grove in Kasargod, and a plasticine caterpillar displaying bite marks from predators. Images by Bhavya Lakshmi.
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