AsianScientist (Mar. 14, 2025) – Changing just a few aspects of an ecosystem can have cascading impacts. Take grazing animals for example – replacing wild herbivores with livestock leads to changes from plant composition down to the characteristics of the soil. In a 14-year study published in Ecological Applications, researchers have found that these effects extend to insects, disrupting spider populations while grasshoppers, ticks and mites thrive.
“Wild herbivores were once ubiquitous across the Earth. Now, they are restricted to a few parks and reserves. Everywhere else, domesticated animals are now dominant,” said Sumanta Bagchi, Associate Professor at the Centre for Ecological Sciences (CES), Indian Institute of Science (IISc) and corresponding author of the study.
In the Spiti region of the Himalayas, Bagchi and his team fenced off plots of land to study the impact of replacing native herbivores like the yak, bharal, and ibex with local livestock. They tracked over 25,000 insects, as well as analysing vegetation and soil conditions, seeking an understanding of how the identity of grazing animals affects ground-dwelling arthropods.
Grazers alter the ecosystem around them, reducing food availability for other herbivores and changing the proportions of plants growing in the area. “Vegetation and soil biotic and abiotic variables are intertwined in complex ways that we are still unravelling. Arthropods heavily depend on them for food and home, an association developed over centuries with native grazers in the ecosystem,” said Shamik Roy, former PhD student at CES and co-first author. This connection can be disrupted when livestock replace wild grazers.
“One of the most surprising observations was the massive difference in tick and mite abundance between native grazers and livestock,” said Pronoy Baidya, former PhD student at CES and co-first author. As blood-feeders, ticks and mites are vectors for a range of diseases, including zoonotic diseases that spread from animals to humans. This livestock-associated increase in population has concerning implications for both animal and human health.
While ticks and mites were abundant, spider populations were greatly reduced in the livestock-grazing plots. When spiders disappear, their leaf eating prey thrive. “Spiders are predators; their ecological roles are similar to wolves, lions, and tigers. A low abundance of spiders can release grasshoppers from predator control, and lead to many downstream changes in an ecosystem,” said Bagchi. It is still unclear why exactly the spider population is affected in this way, but the team speculate that altered plant composition could hinder their ability to capture prey, reducing their source of food.
The researchers highlight the need to rewild native herbivores, as well as improved surveillance of vector-borne diseases in areas where humans and animals coexist closely. They also advocate for more effective conservation policies for areas with large-scale livestock grazing.
“Currently, most of the commons are rather mismanaged, allowing people from villages to unsustainably utilise these commons for their livelihoods, and in the process denying the local herbivores their grazing areas,” said Baidya. “Our study will hopefully be an example which may nudge governments to take serious steps for freeing up the commons first and then starting proper ecological restoration of these lands.”
—
Source: Indian Institute of Science ; Image: Shutterstock
Disclaimer: This article does not necessarily reflect the views of AsianScientist or its staff.
