Imagine. Imagine the journey of a wild tiger, its lustrous orange fur eluding exposure in the grasses, branches, and ridges it traverses. Daintily yet steadily stalking its prey, gracefully yet ferociously securing its next meal, all the while trusting its natural impulse to trek forward. But what is this drive to continue trekking? Is it the faint whiff of a potential mate nearby, the fervid desire to protect an established territory or perhaps the familiar rumble of hunger? In any case, the freedom of vast, minimally disturbed habitat has become increasingly difficult to obtain with the expansive degradation and fragmentation of land. As a result, its journey is sporadically diverted if not halted by whizzing vehicles on unfamiliar roads and the crashing of trees alongside whirring machinery. Onward it travels, though, progressively evading this onslaught of disruption by discovering sheltered routes and corridors to reach its destination eventually.

Our tiger, one of only approximately 4,500 wild tigers in the world, shares a similar journey to its peers. Over the past few decades, increasing human populations and dramatic land-use changes have contributed to massive amounts of deforestation and habitat fragmentation in critical tiger habitats, leaving small, isolated populations at high risks of inbreeding and local extinction. These are global issues that not only imperil the future viability of entire populations of this culturally significant species but also disrupt whole ecosystems when the land can no longer support them. This pattern of habitat loss has enormous global implications as well, as continued deforestation further exacerbates the negative effects of climate change and increases human-wildlife interactions and conflict. 

While humans are the greatest threat to tigers, we also provide the greatest hope for their survival. One tiger conservation strategy is the creation and maintenance of wildlife corridors, which are strips of natural habitat that connect populations separated by anthropogenic pressures. Corridors play essential roles in providing landscape connectivity critical to increasing gene flow between separated populations, decreasing overall extinction risk in species threatened by deforestation and fragmentation, and maintaining biodiversity levels critical for continued ecosystem health. While there are concerns that corridors can increase the risk of introduced pathogens and predators, increase fire risk, and exacerbate edge effects, the benefits seem to outweigh the drawbacks. 

Fractured landscapes

Tiger landscapes are extremely fragmented due to increased urbanisation, road infrastructure development, and agricultural expansion. These threats are detrimental and ongoing. For example, future large-scale road systems such as China’s Belt and Road Initiative and Sumatra’s Trans-Sumatran Highway as well as many other small-scale road developments will continue to cut through tigers’ remaining range, exacerbating habitat fragmentation, poaching access, prey depletion, and direct mortality through vehicle collisions. Some tiger habitats have suffered from these growing threats more than others, including Rajaji National Park in the far-western Terai Arc Landscape and Ranthambore Tiger Reserve in India, Khao Yai National Park in eastern Thailand, and Way Kambas National Park in southwestern Sumatra. Tigers are assumed to have been extirpated from Khao Yai, just as they have previously been in Cambodia, Laos, and Vietnam. Tiger individuals in Rajaji, Ranthambore, and Way Kambas have been separated from adjacent populations for so long that they are suffering from the negative impacts of inbreeding and are no longer able to successfully survive and reproduce as a population over time. These small populations require the assistance of genetic rescue through translocations of genetically differentiated populations to become once again genetically viable.

Isolation

Tiger populations that have been isolated from other populations for long periods of time have been shown to demonstrate many unique negative effects. High levels of inbreeding are common for small, isolated populations like those aforementioned as well as the tiger population in Ranthambore Tiger Reserve in India. These populations accumulate harmful alleles, or variations of a gene, that have been inherited by descent from related parents, which reduces population fitness. One extremely unique physiological response to isolation can be found in the tiger population of Similipal Tiger Reserve in eastern India, where over one-third of all tigers are pseudomelanistic—a variant of pigmentation expressed in these tigers as wide and fused black stripes that alter their primary colour from lusty orange to black. This trait is a result of the high relatedness between individuals in this population. Another interesting effect of isolation has been the alteration of sex ratios from female-biased to male-biased in Dudhwa and Katarniaghat tiger populations, two other Indian tiger groups. This shift to male-biased adult sex ratios results in increased intra-species conflict between multiple males as well as between dominant males and cubs sired by subordinate males. This increased competition for females due to isolation further threatens the success of these tiger populations over time. 

Fostering recovery

While tiger populations have previously suffered many declines and continue to be challenged by fragmentation and human development, recovery of their landscapes and populations is possible. For example, joint efforts between Russia and China to ban logging, improve anti-poaching efforts, and decrease human densities within the Lesser Khinghan Mountains, the Laoyeling landscape, and the Wandashan Mountains has significantly increased tiger populations and has encouraged greater levels of resettling across these landscapes. In Rajaji National Park in India, tiger populations tripled over 13 years with tigers occupying almost 90 percent of available habitat after a program voluntarily relocating pastoralist communities took place, replacing these previously livestock-rich areas with protected areas connecting Rajaji National Park with Corbett National Park. In Huai Kha Khaeng Wildlife Sanctuary in Thailand, intense wildlife management and protection efforts over five years has allowed this landscape to hold the largest breeding population and density of tigers in Southeast Asia and to become a source site for replenishing tiger populations across the entire Western Forest Complex.

Reconnecting landscapes

Conservation initiatives have recently been crucial to many successful landscape reconnections. The Khata Corridor connecting Bardia to Katarniaghat Wildlife Sanctuary in India, for example, was meticulously developed from a contiguous series of 74 community forests. Conservation organisations like World Wide Fund for Nature Nepal initiated early restoration efforts in this landscape alongside local communities in 2001, in the hopes that income-generating sustainable livelihoods would garner additional support and stewardship. This plan succeeded, and many local communities have since been working to protect this corridor system for both their own livelihoods and the continued survival of native wildlife populations. 

Another significant landscape reconnection is the RIMBA initiative, which currently provides the sole linkage between many east-central tiger habitats and west-central protected areas in Sumatra. This region’s surrounding non-protected landscapes possess some of the highest deforestation rates in the world, which has contributed to significant difficulty in maintaining the corridor’s functionality. However, organisations such as the Wildlife Conservation Society, Fauna & Flora International and World Wide Fund for Nature Indonesia are devoted to upholding effective management in this region by continuing to work with local communities and improving monitoring technology. 

Reconnecting landscapes can be very challenging due to factors such as ineffective leadership, poor communication and action planning between governments and local communities, and lack of accountability. However, the growing field of connectivity conservation is working toward counteracting these challenges to implement successful projects devoted to protecting and establishing ecological connectivity, and the most successful connectivity conservation plans are enhanced by leadership continuity, stakeholder steadfastness, legislative mandates, goal specificity, adequate funding, and public outreach. Coalitions of scientists, conservationists, and concerned citizens can contribute to this cause and support tiger connectivity conservation by (1) donating to initiatives committed to tiger corridor development and maintenance, reforestation efforts, and tiger protection; (2) supporting local and national legislation devoted to habitat protection; (3) leading or assisting focal media campaigns to garner support for connectivity action; and (4) incorporating connectivity into plans for network expansion.

Imagine once again. Imagine the journey of the world’s wild tigers. Consider how your actions impact them and what steps you could take to safeguard their treks starting today.

Further Reading

Carter, N., A. Killion, T. Easter, J. Brandt, and A. Ford. 2020. Road development in Asia: Assessing the range-wide risks to tigers. Science advances 6(18): eaaz9619. 

Harihar, A., B. Pandav, M. Ghosh-Harihar, and J. Goodrich. 2020. Demographic and ecological correlates of a recovering tiger (Panthera tigris) population: Lessons learnt from 13 years of monitoring. Biological conservation 252(1): 108848.

Keeley, A., P. Beier, T. Creech, K. Jones, R. Jongman, G. Stonecipher, and G. Tabor. 2019. Thirty years of connectivity conservation planning: An assessment of factors influencing plan implementation. Environmental research letters 14(10): 103001.

Photos: Wikimedia Commons