Big wild herbivores like jumbos, bison and rhinos can protect local nature by eating and trampling on biodiversity-threatening invasive plant species, researchers from the Uttarakhand-based Wildlife Institute of India (WII) and Aarhus University in Denmark have concluded after assessing huge data gathered from the world's largest wildlife survey conducted in India.
Regarding native plants, they said, that these have evolved in such a way that they can withstand brutal treatment from species of herbivores they have co-existed with for millennia, while invasive plants usually cannot. Their study is published in the scientific journal, Nature Ecology & Evolution.
The researchers used a battery of 26,838 camera stations and 158,979 vegetation plots to assess the relationships between megaherbivores, native plants and alien plants across India sprawling over 121,330 km2 of area.
The study is based on what the researchers call mega-herbivores, i.e. animals weighing more than one ton. In India, these are elephants, rhinos, wild water buffalo and Indian bison (the largest and heaviest bovine in the world).
However, the researchers also pointed out that the results are also relevant for areas that do not have herbivores quite as large as those in India.
The study demonstrates a positive correlation between the number of mega-herbivores and the balance between native and invasive plant species: Where there are many mega-herbivores, there are also many native plants and fewer invasive plants. Because their large size means that they have to eat a lot. And they are used to eating many different plant species, even species with less nutritional value, because they simple cannot afford to be picky. Therefore, they are more likely to include unfamiliar plants in their diet.
The study's lead author, Ninad Avinash Mungi from Aarhus University, however, stressed that "You can easily use a mixture of large, medium and small herbivores. Deer, buffalo, cattle and horses work well together in rewilding projects, and together they can also target different invasive plant species. This also makes efforts more flexible and resilient," he said.
“Megaherbivores, with broad dietary tolerances, could remove large biomass of established plants, facilitating new plant growth…This relationship was strongest in protected areas with midproductive ecosystem and high megaherbivore density but it was lost in areas where thicket-forming alien plants predominated (>40% cover),” said Qamar Qureshi, co-author and senior wildlife expert from the WII.
His colleague from WII and also co-author of the study, Yadvendradev V Jhala added, “by incorporating the role of ecosystem productivity, plants traits and densities of megaherbivores on megaherbivore–vegetation relationships, our study highlights a function of megaherbivores in controlling alien plant proliferation and facilitating diverse native plants in invaded ecosystems.”
The study holds importance for biodiversity rich countries like India where unchecked growth of the invasive plant species are threatening native flora and fauna. The United Nation has designated invasive species as one of the five most important threats to global biodiversity. Invasive species are animals, plants and fungi that are introduced to areas to which they could not spread themselves, and that also harm native biodiversity.