Over the last decade or so, numerous accounts have emerged from India to illustrate the perilous state of its endangered tiger populations. Perhaps the most high profile of these surrounded the extirpation of tigers from the Sariska reserve in Rajasthan in 2004, an event that proved to be the catalyst for a fundamental review of conservation policy in India. The most poignant story I have heard from this period, however, emerged via Prerna Singh Bindra in her book ‘The King and I’. Reporting from one of the lesser known reserves, Palamau in the state of Jharkand, Bindra recounted the sad tale of Rani, a six year old tigress. She was the last remaining member of her species to inhabit the park and she continued to patrol her territory, issuing a series of plaintive calls to attract a suitable mate that no longer existed, oblivious to the futility of her situation. Reality dictated that Rani was doomed to live out the rest of her life in isolation, the last of her kind. The reason behind her enforced solitude was not difficult to comprehend as Palamau had become a virtual island, its connectivity with outlying habitat blocked by a combination of human encroachment and development. The despondency of this tale is compounded by the inescapable fact that such episodes are likely to increase in the future as the permeability of tiger reserves becomes further compromised. And, once critical dispersal corridors are lost, they are notoriously difficult to recreate.
David Quammen offers an interesting analogy in this regard, likening the habitat matrix to that of a Persian carpet. In its entirety, the pattern of the carpet is clear, flowing seamlessly across its surface. Imagine though, taking a knife to the carpet and slicing it into a series of smaller squares. The pattern is now disrupted, each edge of each fragment fraying and unravelling further over time, the gaps between becoming more pronounced. Even the most experienced of restorers is unlikely to be able to replicate the original pattern, to fuse the frayed threads back into a semblance of its former connectedness. This is the same for a tiger landscape and, to add a further dimension, the area of decline in each of the remaining habitat fragments becomes subject to an increasing edge effect. In order to explain this phenomenon, let us return to the example of the carpet. Say, in its original state, the carpet measures 10 metres on each of its four sides. This gives us a total edge of 40 metres. It is this area that is more prone to deterioration than any other portion of our carpet and we can see from a quick glance that it has been strengthened by an extra layer of stitching to prevent it from scuffing and fraying. Now, say we cut the carpet into one metre squares and lay these individual fragments side by side in an approximation of the original design. Now, the edges of our individual remnants add up to 400 metres, a ten-fold increase. When the metre-square fragments are initially laid side by side they may fit closely together with only small fissures between, but as the cumulative effects of foot traffic act upon the fabric over time, so the individual edges are revealed and erode at a faster rate. Returning to the core issue of our eroded tiger reserves, this process of fragmentation leaves the remaining habitat patches prone to increased human encroachment and industrial infiltration, accelerating the rate of decline. What were once uninterrupted habitats harbouring healthy tiger populations become a series of disconnected islands as, as we have seen in the previous post, this leaves resident tigers increasingly susceptible to the pernicious effects of inbreeding depression.
The previous article entitled ‘Cat of 9 Tails’ focused on the thorny issue of taxonomic inflation, recognising that the subspecies approach may have inadvertently contributed to a depletion in genetic diversity across the tiger’s geographical range. Today, in India, it is claimed that tigers now occupy a mere seven percent of their historical habitat and that over 90 percent of their number are restricted within the country’s network of protected reserves in at least 76 discrete groups. Two recent studies published in the ‘Proceedings of the Royal Society B’ in 2013 suggest that, in India at least, this has occurred as a result of an ongoing decline in connectivity between increasingly isolated units of tiger habitat.
Loss of habitat has long been viewed as a major obstacle to effective tiger conservation but it is arguably its fragmentation that has exacted the greatest toll on the big cats. A fundamental understanding of tiger culture and behaviour reveals how the blocking of key dispersal routes has led to insularity in modern day tiger populations, an issue that may have dire repercussions for the long-term persistence of the species. In the first paper, researchers studied historical levels of mitochondrial DNA found in tigers that had been hunted during the period of the British Raj, now contained in museums, and compared the data against those of their modern day descendants. Their findings suggested that, over the intervening period, genetic heterogeneity had declined and that only 93 percent of historical DNA variants remained.
Michael Bruford, one of paper’s co-authors, emphasised the link between this loss of diversity and the partitioning of tigers in small pockets of protection that have lost connectivity to outlying forests. “This will not go away until wild places are managed coherently” he argued, adding that the Indian authorities needed to rethink the way in which it measured conservation success, rather than continue to restrict its focus on tiger numbers alone. The second paper picked up on this theme, focusing on tigers inhabiting different zones of the Satpura – Maikal landscape of central India, investigating their genetic make-up to ascertain the extent to which corridors were functional or not. Their results pointed categorically towards the fact that the highest rate of gene flow coincided with sites displaying the greatest habitat connectivity. This, the authors argued, had major implications for conservation policy and practice, consistent with an emphasis on landscape-level protection measures. Here, the broader theme of source-sink dynamics needs to be considered.
Source populations describe those tigers occupying prime habitat in the core areas of inviolate reserves, utilising the available space to establish their territories in prey-rich, protected landscapes suitable for breeding. As their numbers grow, older tigers can become displaced through territorial contest and, as they mature, sub-adults are forced to disperse in order to establish their own territories. In each case, areas on the periphery of reserves act as transit routes, and to be effective, need to connect other source areas to maximise the potential for genetic exchange. The areas between these source locations are known as sinks and these zones contain transient tigers seeking to disperse. They can therefore be seen as sites of potential conflict as tigers come into contact with humans communities living in close proximity to the reserves. It is within these buffer areas through which transient tigers pass, and sometimes settle, that are referred to as sinks. Here, the habitat is less secure and subject to enhanced levels of human presence and associated development pressure. It is also these areas that have become an arena in which a variety of human-tiger conflicts are played out, particularly in those spaces where critical corridors have been disrupted, effectively trapping tigers within human-dominated environments. Remedial activity within these sinks is therefore viewed as a prerequisite in the broader battle for tiger survival.
Action to rehabilitate sink areas has tended to play a secondary role to the protection of source populations. This focus on the core areas of tiger reserves is of vital importance as, without successful breeding, movement beyond protected area boundaries remains limited. However, given the reported resurgence in tiger numbers reported in the All-India Tiger Estimation of 2014, the stocking density of certain tiger reserves is rapidly approaching saturation. In this case, the presence of transient tigers seeking to disperse is generating increasing pressure in the sinks. The task of rehabilitating these passages, however complex it may be, is therefore of vital importance to any landscape-level conservation approach. Rigid adherence to the conservation of source populations is no longer a viable proposition and it can be argued that forest officials are currently doing just half the job and that action in the sinks is now imperative. As intimated above, though, this is far from a simple task. There are major hurdles involved in the re-establishment of an appropriately linked-up landscape matrix in sink areas.
These buffer zones are designed to be multiple use in nature and contain human settlements and the supportive infrastructure required to survive in what are perceived to be hostile environments. Marginalised local communities often rely on the availability of firewood to meet their energy needs, also utilising the space to rear and graze their livestock. Here, cattle and goats compete with tiger prey for resources and, in the absence of sufficient prey, domestic livestock becomes an alternative food source for tigers, heightening the potential for conflict.
The future of these sinks remains under pressure for development and, just as its difficult to turn back the clock, it is virtually impossible to hold back time. Recent reviews of india’s inability to sustain its economic growth rate have identified the relative paucity of infrastructure as a determining factor in its failure to match China’s meteoric rise as a global economic powerhouse. This understanding will inevitably contribute to more pressure for infrastructure in and around tiger reserves, evidenced by recent developments in the Kanha-Pench landscape, subject to the construction of National Highways 6 and 7. Effective planning is crucial to such developments and, in an effort to reduce their impacts on endangered wildlife, the introduction of a smart green infrastructure (SGI) approach is essential. SGI is a planning mechanism and is based on the identification of a hierarchy of mitigation responses, consisting of four distinct options: avoidance, minimisation, restoration and offset. These categories reflect the extent to which any proposed infrastructure is required and provides planners with a series of options in countering the associated decline in habitat connectivity as a consequence of development. Roads are undoubtedly a threat to tiger dispersal.
While road kill incidents remain comparatively rare, highways nevertheless create a major barrier to tiger mobility and can fracture historical dispersal corridors. Proponents of SGI claim, however, that new developments of this kind may also provide an opportunity to enhance connectivity, while opponents view it as just another justification for development to take place in vulnerable natural venues.
Let us now consider some of the benefits that may accrue from the adoption of the SGI process. Firstly, it embeds wildlife concerns into the planning process and creates a situation, in theory at least, where applications may be refused, or roads re-routed, if they are deemed to be detrimental to conservation objectives. Secondly, if such developments do receive a green light, which they inevitably will in most cases, then the SGI process demands that minimisation of resulting disruption must be considered and acted upon. This is perhaps more feasible than the avoidance option. Restricting our focus to the construction of roads it is useful at this point to consider one potential scenario. In places where transport networks intersect with key migration routes, it is possible to construct underpasses or to raise the level of roads to enable the safe passage of wildlife. Where potential accident hotspots can be identified, these can be fenced off in order to channel animals towards safer crossing points where strict, enforceable speed regulations can be imposed. This could be supported by the fitting of CCTV technology to monitor not just speed transgressions but as an early warning system to the presence of suspected poachers. In recognition of the expanded edge effect that such developments create, the issue of compensatory and offset investments can be used not only to fund increased patrols in vulnerable areas but also to provide services to local communities. This is vital in areas where human-tiger conflicts are deeply entrenched and may prove to be a way in which to reduce the incidence of such conflict and build support for wildlife within these marginalised communities.
At present it is unclear how successful SGI will prove to be in protecting vulnerable tiger corridors. Indeed, in India, it remains far from certain that it will even be adopted as a central component of the planning process. What is clear, however, is that in the absence of remedial action in sink areas, tiger landscapes are likely to lose their connectivity altogether.
Today, these areas are subject to no legal protection and concern is thus mounting that the fabric of tiger habitats will become increasingly frayed, unravelling at a greater pace over time as development opportunities are taken up. Without action being taken to reverse this trend, there are two outcomes that are likely to emerge. First, emphasis on the exclusive protection of source sites may culminate in tigers existing as boutique populations, requiring enhanced levels of human intervention to effect the levels of genetic exchange sufficient to perpetuate the species over the long-term. The resulting tiger groups may become, to all intents and purposes, captive, existing merely for show to the hordes of tourists descending on the remaining showcase parks. Second, the tiger may be abandoned to its own devices, left to slowly succumb to the injurious effects of inbreeding depression. Here, we may be creating more Ranis, isolated tigers forced to wander aimlessly down roads that lead nowhere, waiting impotently for the demise of their species. Neither scenario provides much hope for the future of the tiger in the wild, so it is vital that we act now to protect and, where needed, restore our carpet, to reconnect all of its fibres to make it as complete as possible, before decay becomes irreversible and the tiger becomes lost to the wild forever.