- A study on tigers in Central India has shown that in the current scenario of unplanned development, the genetic variability of tiger populations — which determines the ability of a species to adapt to future changes — will decrease.
- Tiger populations in small, isolated protected areas run the risk of local extinction.
- Measures such as restoring and protecting corridors between PAs, and adding a buffer zone around the smaller populations can reduce extinction probability.
- Looking at whether animals are using the corridors provided — called ‘functional connectivity’ — is more important than corridors existing on paper.
About six years ago, a tigress was rescued from an irrigation canal in the western state of Maharashtra in India. Radio-collared by a scientific team, led by Vidya Athreya from Wildlife Conservation Society–India Programme, the tigress and the path she walked for a year pulled back the veil that concealed the lives of these carnivores. What it showed was, perhaps unsurprisingly, that she was much more cognisant of, and perhaps comfortable with, human presence than vice versa. She lived and travelled through a human-dominated and highly fragmented landscape, including villages, roads and croplands. While in the daytime she rested in dense forest patches, most of her active time was nocturnal.
Tigers in India live and have to find ways of survival and movement through a human-dominated landscape. Though afforded protection in tiger reserves, about 35 percent of India’s tigers are estimated to live outside protected areas (PAs). Most of India’s land (95 percent) lies outside these protected areas, and the future of these regions and the changes they undergo will have a significant role to play in tiger conservation, shows a recent paper in Biological Conservation.
The paper, led by Prachi Thatte from the National Centre for Biological Sciences (NCBS), confirms that in the current scenario of unplanned development, the genetic variability of tiger populations, which determines the ability of a species to adapt to future changes, will decrease. Small, isolated PAs will run a high risk of local extinction.
The challenge: maintaining connectivity
India is a dynamic landscape. Except for high altitude or inhabitable or protected areas, it would be hard to imagine a place in status quo for long. And if we add a high growth rate, rapid urbanisation, increasing human densities and associated population pressures on land, maintaining connectivity of PAs is a tough ask. The study finds that habitat connectivity, sub-populations that allow migration, and an increase in population numbers would lead to lower extinction probability.
In the current, rapidly changing land use scenario in India, the paper provides a way to evaluate alternative futures and their impacts on tiger numbers and connectivity. Such approaches can be useful in planning future policies. Considering the imminent, infrastructural changes across India, this gives an essential means to evaluate the impact of proposed infrastructure development quantitatively.
“International policies and targets consider tigers across their range, while the realities and challenges of tiger conservation may be different in various parts of their range,” commented Uma Ramakrishnan, a molecular ecologist at NCBS and a co-author of the paper. “In India, increasing the number of tigers is critical, but, equally important is trying to understand the dynamics of the tiger population in landscapes, which represent sets of connected tiger reserves. Our paper reveals that changes in future landscapes will affect not only tiger connectivity but also their numbers. In other words, the two are inter-linked. Recovery of tiger numbers alone is not sustainable in the absence of connectivity.”
For the study, Thatte and her team collected 580 scat samples from tiger potential areas in the Central Indian Landscape (CIL), which is estimated to have about 700 tigers. The genetic analyses of these samples at a landscape level allowed them to infer what impacts connectivity and thereby genetic variability. And looking towards the year 2100, the team ran future simulations with varying land use change and management scenarios, to understand future connectivity, genetic variability, inbreeding and eventual extinction. The simulations included 11 unsampled protected areas as well, areas that either host tigers or have a high probability of tiger occupancy.
A map showing the study area — The Central Indian Landscape. From Google Maps.
Small populations face the highest risk
One of the primary reasons Thatte wanted to conduct this study is to know what we need to do now to avoid extinctions in the near future. And according to the study, there is a high probability that tigers will go extinct in small tiger reserves such as Bor in Maharashtra.
“Local extinction is what contributes to overall declines. Mammal populations have been declining worldwide. What we see for tigers in CIL is that extent of smaller populations in this landscape leads to high genetic differentiation. The connectivity between large and small areas is critical, and populations which are sensitive are the smaller or the isolated ones; the ones which contribute to the overall health of populations,” she said.
Peering into the future using simulations, the study shows that overall genetic diversity reduced over time in all the simulation scenarios. But adequate measures such as restoring and protecting corridors between PAs can temper this reduction. Adding a buffer zone around the small, currently connected populations reduced the extinction probability to a large extent. However, reducing the dispersal limit, or the maximum distance a tiger can disperse, from 500 km to 300 km in the simulations doubled the average extinction probability of some populations, such as Melghat and Bor. This means that the distance a tiger can move has a strong effect on its survival.
So, can adding a buffer reduce the need for connectivity? No, said Ullas Karanth, director for Science-Asia, for the Wildlife Conservation Society, New York and a part of the Athreya study. “Increasing the buffer will – given normal protection – reduce human impacts, increase space, and potentially increase the tiger population, making the population less vulnerable to ‘demographic’ extinctions such as the ones in Sariska. Corridors, on the other hand, will make the population more robust to potential genetic deleterious effects in the longer term. Both are good, but if the amount of resources is finite, this becomes a trade-off,” he added.
Athreya’s study has shown that tigers do move through coffee, sugar cane and some other crops. Therefore, adding ‘forested government-owned buffers’ may not necessarily be the only possible solution.
The practical considerations of corridors are essential, and they need to be urgently planned along with development projects in India, especially in the context of highway construction and other linear disturbances of protected areas. Road traffic is estimated to grow at about 13 percent per annum over the next 20 years. According to past research as well as Thatte’s paper, human impact is the most significant cause of tiger declines. The paper states that dense human settlements and roads with high traffic are the most resistant to tiger mobility, while degraded forests and plantations offered negligible resistance and agriculture-village matrix offered low resistance. Though tigers seem to tolerate some level of agriculture-village matrix, very large swathes of this land use could impede movement.
Not quite what it seems
What we might consider as corridors viable for wildlife on paper, for instance forest patches, are different from the more important “functional connectivity”, i.e. whether the animals are using the corridor. And this can depend on a lot of factors.
Karanth said, “As far as tigers are concerned, the availability of prey species to feed on while they disperse, and, the absence of persecution if they kill livestock during dispersal through human-dominated landscapes, are critical factors. Type of cover etc. are less important as tigers can disperse at night, over long distances and through plantations, many crops etc.”
What we do know is that these corridors need to be protected them from all threats, degradation, poaching, traffic etc. Sanjay Gubbi, a conservation scientist with the Nature Conservation Foundation, Mysore, has extensive experience with connecting tiger habitats, and has helped join 2,500 sq km of tiger habitat together. He echoed that many of the corridors lie outside protected areas hence do not receive the same legal protection as a protected area, and are often diverted for infrastructural development with little understanding of their importance. Thatte mentions that while delimitation for corridors has been done, they are yet to be legally notified.
“Lot of these areas might be fine in next 10-20 years but tiny ones, like Bor, which has very less forest area around it, are vulnerable. These are the areas that need immediate attention. Legal notification would result in some protection or monitoring regime, which is critical,” Thatte added.
The features of corridors cannot be universal since the demands from these areas are varied. Since the land use matrix and the demands from these land resources are varied, no single solution can be applied to all areas. Gubbi gives a real-life example. At present, he is working on solutions for providing mobile phone and LPG connections to villages around Malai Mahadeshwara Wildlife Sanctuary (MM Hills). But what does this have to do with tigers? It is because this area provides a vital connection between MM Hills and the BRT Tiger Reserve. Moreover, it is also an area under degradation because of fuelwood extraction, which will eventually affect the quality of the corridor. Gubbi added, “By reducing this degradation we hope to improve and strengthen this corridor.”
Across the tiger landscape in India, a large number of these critical threads are at risk of fraying and eventually disappearing. To keep this tiger tapestry alive, we need to fortify these connections and allow secure mobility. “We need to notify corridors for long-term survival. If you notify these after 30 years, the area would have changed a lot because there might not be other areas from where smaller areas can be repopulated,” said Thatte.
Banner Image: A tiger in Central India. Photo by David Raju / Wikimedia Commons.