‘Alien species cause sudden disruption’

Like humans, ungulates—the most important prey base for large carnivores—need calories, proteins, minerals and vitamins. But unlike us, they have a secret weapon: the ability to digest cellulose. This fibrous plant material, tough to most, becomes a feast thanks to specialised bacteria dwelling in either their foregut (ruminants) or hindgut (colon and rectum). In temperate regions, ungulates are limited by energy, but in the tropics the limiting factor is proteins. This constant tug-of-war drives an incredible evolutionary race between plants and herbivores.

Plants evolve defences to prevent herbivory and ungulates evolve ways to overcome these defences. One important plant defence mechanism is using chemicals that can be toxic on consumption. Over thousands of years, mechanisms in ungulates evolved to tolerate or detoxify these chemicals and get to the nitrogen-rich foliage.

The introduction of exotic invasive plants disrupts this coevolutionary balance and native ungulates lose out since they do not have mechanisms to address the novel toxins in the ecosystem. Thus, eating Lantana, for example, beyond a certain proportion of the diet can be poisonous for native Indian species. Additionally, invasive exotics outcompete native flora, diminishing the edible biomass available to native ungulates.

Over vast timescales and sprawling landscapes, ecosystems eventually adapt. Native flora and fauna evolve countermeasures, and ecosystems reach a new, albeit altered, equilibrium. However, human activities complicate this natural process. Rapidly spreading invasives, shrinking habitats and fragmented landscapes leave ungulates facing an uphill battle. Protected area management often advocates creating grasslands from forests to increase the carrying capacity for ungulates, but this practice can exacerbate the problem as grasses have poor nutrient content compared to browse species (a classification of plants and shrubs that herbivores eat) found in the forests. Grasslands in sal forests are an exception since the understory of sal forests have limited nutritive browse species but clearing deciduous miscellaneous forests for making grasslands reduces the carrying capacity of the protected area for ungulates.

Yadvendradev Jhala is the former dean of the Wildlife Institute of India, Dehradun

This column was first published in the January 1-15, 2024 print edition of Down To Earth

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