I previously said that poaching for the Traditional Asian Medicine (TAM) trade is the most immediate threat to wild tigers. But there is another issue that could lead to Panthera tigris’ extinction: habitat fragmentation.
Although tigers are habitat generalists, they are reluctant to cross human-dominated terrain (Smith, 1993). This means that as protected areas in tiger range countries become increasingly surrounded by civilization, tiger populations are becoming isolated (Harihar & Pandav, 2012; Gubbi, Mukherjee, Swaminath, & Poornesha, 2015; Wikramanayake et al., 2011).
Why Habitat Fragmentation Matters
The isolation brought about by habitat fragmentation has serious implications. First of all, it can lead to high levels of inbreeding that will reduce the genetic fitness of a population (Mondol, Bruford, & Ramakrishnan, 2013; Yumnam et al., 2014). Small populations of large carnivores are also vulnerable to human-caused mortality at the edges of protected areas (Woodroffe & Ginsberg, 1998). This may be especially true for tigers. Smith (1993) found that when prime habitat was not available, dispersing male tigers sometimes settled near human-dominated landscapes until a better territory opened up. This carries substantial risks for tigers, and might lead to human-tiger conflict.
Lastly, habitat fragmentation can exacerbate the effects of poaching (Cushman, McRae, Adriaensen, Beier, Shirley, & Zeller, 2013). If populations are isolated, tigers from neighboring reserves cannot help replace hunted individuals. This contributed to the extinctions of tigers in Sariska and Panna reserves in the early 2000’s (Yumnam et al., 2014; Wikramanayake et al., 2011).
The Importance of Corridors
A popular solution to lessen the effects of habitat fragmentation is the establishment of biological corridors. These are pathways of viable habitat that allow animals to move throughout a landscape. Sufficiently protected corridors can encourage gene flow between populations (Mondol et al., 2013; Rabinowitz, 2014), partially offset losses from poaching, and benefit more creatures than just the target species (Yumnam et al., 2014).
Moreover, establishing biological corridors presents an excellent opportunity for community involvement. Local people played an important role in restoring habitat connectivity in the Terai Arc Landscape (TAL) of northwestern India and southern Nepal (Dinerstein et al., 2007). Involving the public in conservation activities has been linked to environmental advocacy (Silvertown, Buesching, Jacobson, & Rebelo, 2013), so it should be pursued whenever possible.
Landscape Connectivity vs Protected Area Security
Given that conservation funding is in short supply, is it better to focus on habitat connectivity or reducing human-caused mortality within reserves?
Ultimately this will come down to what is most necessary in a given area. For example, Yumnam et al. (2014) used genetic testing to determine that tiger populations in central India face imminent isolation. Tigers in Bandhavgarh National Park were already cut off from neighboring reserves. In such a case, immediate action should be taken to reestablish connectivity and safeguard existing corridors.
But tigers’ biological characteristics make them more vulnerable to human-caused mortality than smaller felids (Chapron et al., 2008). This means that in general, poaching within protected areas should be addressed first. When tigers are not sufficiently protected their numbers decline: sometimes drastically. Therefore poaching within source sites must be brought under control in order to allow for healthy dispersal behavior (Walston et al., 2010).
In 2010, all 13 tiger range countries vowed to double wild tiger numbers by 2022 (GTRP, 2011). To my knowledge, this is the first time the world has united so strongly for a single species.
Poaching of tigers must be significantly reduced in order to ensure their short-term survival. But once adequate protection has been established in a location, landscape-level connectivity needs to be secured. Of course this is a general strategy, and it may have to be altered to fit specific situations.
Above all, conservationists should continuously monitor the effectiveness of their interventions. This will allow them to identify the actions that will most effectively lead to a better future for both people and tigers (Pullin, Sutherland, Gardner, Kapos, & Fa, 2013).
Cushman, S. A., McRae, B., Adriaensen, F., Beier, P., Shirley, M., & Zeller, K. (2013). Biological corridors and connectivity. In D. W. Macdonald and K. J. Willis (Eds.), Key Topics in Conservation Biology 2 (384-404). West Sussex, UK: John Wiley & Sons, Ltd.
Yumnam, B., Jhala, Y. V., Qureshi, Q., Maldonado, J. E., Gopal, R., Saini, S., … Fleischer, R. C. (2014). Prioritizing tiger conservation through landscape genetics and habitat linkages. PLoS ONE. http://dx.doi.org/10.1371/journal.pone.0111207.
Walston, J., Robinson, J. G., Bennett, E. L., Breitenmoser, U., da Fonseca, G. A. B., Goodrich, J., … Wibisono, H. (2010). Bringing tigers back from the brink – the six percent solution. PLoS Biology, 8(9): e1000485. http://dx.doi.org/10.1371/journal.pbio.1000485.
Wikramanayake, E., Dinerstein, E., Seidensticker, J., Lumpkin, S., Pandav, B., Shrestha, M., … Than, U. (2011). A landscape-based conservation strategy to double the wild tiger population. Conservation Letters, 4, 219-227. http://dx.doi.org/10.1111/j.1755-263X.2010.00162.x.
Woodroffe, R., & Ginsberg, J. R. (1998). Edge effects and the extinction of populations inside protected areas. Science, 280, 2126-2128.