Grazing and invasive species impact food availability for wild herbivores in MM Hills, finds study

Wild elephants grazing in MM hills. Photo by Dincy Mariyam.

  • Researchers reconstructed the diet of wild and domestic herbivores in MM Hills, Karnataka, using environmental DNA to understand dietary niche overlap.
  • This method of study is expected to generate a detailed diet of herbivores, analyse their fecal matter in a non-invasive way and remove the difficulties in traditional methods, according to the authors.
  • The study finds that an increase in the spread of invasive alien species is increasing the competition between domestic and wild herbivores in resource sharing and partitioning.

In October 2022, two elephants were electrocuted to death in Assam. Further investigation revealed that this accident had occurred while the tuskers were foraging in areas with heavy human habitation. In the last decade up to December 31, 2020, more than 1,160 elephants have died in India due to human interventions. In the wild, elephants and all other mammal populations are threatened due to habitat degradation, Invasive Alien Species (IAS) and hunting/poaching. In addition to this, domestic herbivores and their presence also impacts wild herbivores.

India is home to seven to eight percent of global mammalian species and of these, over 150 species fall within the Schedule I and II categories. India is also home to about 162 different breeds of domesticated animals. A recent study  that explored the relationships between cattle and biodiversity in a multiuse landscape exposed that domesticated herbivore mammals can create disequilibrium in the wild due to overlapping feeding patterns and livestock density in Protected Areas (PAs).

Grazing in Protected Areas 

In India, livestock grazing and non-timber forest products (NTFP) collection by local and indigenous communities are permitted in many PAs and are protected under the Forest Right Act (2006). “Livestock contributes towards providing nutritional and economic security to the communities and is a major part of their various traditional agricultural practices. However, apart from such communities and traditional forest dwellers in several instances, herders from outside PAs occasionally camp inside forests to graze their livestock, which is banned in many PAs,” says Siddappa Setty, who has been working with communities in PAs across India for over two decades.

The coexistence of domestic and wild herbivores comes with its challenges. “Global studies indicate that wild herbivores are threatened by growing livestock grazing in PAs for two major reasons. Firstly, rampant grazing in reserved forests leads to habitat loss for wildlife, which leads to crop raids by wild herbivores in the neighbouring agricultural areas. Secondly, there is a possibility of infectious diseases spreading from the domestic to the wild (such as foot and mouth disease),” says G. Ravikanth, Senior Fellow at ATREE, a research trust in Bengaluru.

eDNA based exploration

The Malai Mahadeshwara Wildlife Sanctuary (MM Hills) in Karnataka is an important elephant corridor and home to longstanding tribal communities and their livestock. Domestic herbivores live close to wild herbivores at the sanctuary, which is also an extension of the Biligiri Ranganatha Swamy Temple Tiger Reserve (BRT). Previous reports from the study area have highlighted the potential impact of livestock grazing in MM Hills, creating the risk of food shortage and spreading diseases. “Resources for wild and domestic herbivores have reduced because of the invasion of Lantana camara in the MM Hills region,” says Setty.

The lush forests of Malai Mahadeshwara Wildlife Sanctuary in Karnataka. Rampant grazing in the reserved forest has an impact on the habitat of wild herbivores, according to a study. Photo by Dincy Mariyam.

Domesticated herbivores generally have a competitive advantage over local wild herbivores owing to the support they get from supplemental feeding during periods of scarcity. However, rampant illegal grazing in the forests leads to the loss of fodder for wildlife, especially during the drought years. This could not only impact their survival but also result in human-wildlife conflict . Due to this increase in pressure and the dietary overlap between wild and domestic herbivores, wild herbivores are at risk. This called for a study to assess the risk posed by domestic herbivores to wild herbivores in MM Hills.

The advancement of genomics and the wider availability of data now make it possible to solve complex ecological problems with genetic tools. eDNA (Environmental DNA) metabarcoding is used widely for various biodiversity monitoring projects globally. “The traditional methods involve: (a) direct observations of the animals, (b) looking for undigested and identifiable plant remains, or (c) looking at the gut content. All of these methods are either too time-consuming or invasive. However, eDNA methods are faster, more reliable and provide much more information than any of the traditional methods,” states Ravikanth, who is also a co-author of the study that employed eDNA metabarcoding to understand the diet of herbivores.

In this study, eDNA techniques utilised fecal matter for DNA isolation and amplified the DNA in the feces samples. The undegraded plant DNA present in fecal matter was extracted using meticulous DNA extraction protocols. The researchers examined a specific section of the DNA (TCL region) and compared it with the reference database to create a plant profile based on fecal matter.

The main findings

The study reconstructed the diet chart of ten herbivorous mammals from MM Hills. The animals in the study mostly consumed various types of grass (Poaceae), followed by different species of legumes (Fabaceae). The narrower the dietary preferences of a given species are, the more difficult it is for the species to adapt to upcoming changes in habitat and resource availability. The study concluded that elephants (Elephas maximus) and bonnet macaques (Macaca radiata) are the most threatened.

Asian elephants in India are a flagship species and have played a major role in India’s history and culture. A 2015 report that studied the habitat occupancy by the Asian Elephant in the Western Ghats, states that 60 percent of Asian elephants are found in India. Among the Indian states, Karnataka is home to the majority of India’s elephant population. In MM Hills, elephants were reported to be majorly dependent on different types of grasses in their diet, which is similar to other studies from southern India. During the rainy season, they mostly depend on woody plants and graminoids. Livestock such as cattle and domestic goats have a dietary overlap with that of the Asian elephant. Local studies from Bandipur Tiger Reserve and studies from Kenya support this, showing a reduction in large wildlife such as elephants with the increased presence of livestock.

Invasive plant species like Lantana Camara have impacted resources for wild mammals in forests.  Photo by Samratmaina2019/Wikimedia Commons.

The bonnet macaque, a well-known endemic frugivore of peninsular India, is in the vulnerable category of the IUCN Red List. The study showed that they highly depend on leguminous plants (63 percent) and occasionally tamarind, and they had a very narrow diet range. Apart from macaques, several wild herbivores such as wild boar (Sus scrofa), Indian hare (Lepus nigricollis), porcupine (Hystrix indica), sambar (Rusa unicolor) and barking deer (Muntiacus muntjak) have been shown to lose their food to cattle and goats in MM Hills. According to Ravikanth, there have also been several cases of disease transmission from domestic to wild herbivores reported from Bandipur and Nagarhole Tiger Reserves.

“Communities are aware of the impacts that grazing is creating in the wild, but they also need livestock for their nutritional and economic security. It is simply not possible for them to afford modern machines that may substitute for livestock,” says Siddappa. Farmers around the PA also tend to grow economically important crops such as sugar cane, which attracts these wild herbivores outside the PA boundaries.

To mitigate the impacts of domestic herbivores on forest wildlife, better management backed by scientific evidence is necessary. Genetic tools are just one way of understanding what herbivores eat and why, improving our understanding of the current scenario in our PA. “As environmental change continues to threaten biodiversity in the area, the need to continue monitoring both the wildlife species themselves and the interaction between wildlife and domestic livestock becomes more urgent,” the study states.

Read more: Large grass-munching herbivores can stabilise soil carbon

Banner image: Wild elephants grazing in The Malai Mahadeshwara Wildlife Sanctuary. Invasive alien species and livestock grazing are proving to be threat to the wild herbivores population in India. Photo by Dincy Mariyam.

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