NAGPUR: Though habitat loss, prey depletion and poaching have severely affected wild tiger populations, human settlements and roads place greater barriers on tiger dispersal than distance, according to new research by wildlife scientists.
The study was conducted by wildlife biologist Aditya Joshi and wildlife scientists Srinivas Vaidyanathan, Samrat Mondol, Advait Edgaonkar and Uma Ramakrishnan in 2009-10. The report was published on November 6. The study was carried out in six sanctuaries encompassing major tiger populations of Central India. These sanctuaries, Melghat, Pench, Tadoba, Nagzira and Kanha, in Maharashtra and MP and Nagarjunasagar-Srisailam in Andhra Pradesh.
"Genetic assignment tests indicate long-range tiger dispersal. It is on the order of 650km between PAs, which is much longer than up to 200km previously thought," Joshi told TOI.
Joshi said earlier studies had shown tiger abundance was driven by prey density. However, very little was known about tiger dispersal rates, landscape predictors like roads, vegetation, human habitation influencing such dispersal.
In this study, experts combined genetic approaches with landscape ecology to study tiger dispersal between six tiger reserves and examined how the nature of the intervening landscape influenced the dispersal. "We define connectivity as a larger ecological measurement of gene flow from one population to another by immigrating individuals," said Joshi.
The team obtained tiger DNA from faecal samples collected from 6 parks. Tigers are known to use roads and trails for travelling and regularly mark territories by depositing faeces. Existing roads and trails in the PAs were searched for fresh tiger scat.
Each road or trail was sampled only once to avoid recaptures and maximize the number of different individual in any of the area covered. Scat samples were stored in absolute ethanol and the geographical coordinates were recorded in field. The data thus collected was combined with data from 22 other individual tigers sampled in 2008 and seven sampled in 2010 by Centre for Cellular and Molecular Biology (CCMB) in 2010.
"Our results reveal long-distance dispersal by individual tigers of over 690km, suggesting that either the individual or its parents moved this distance. The assignment tests performed in scat reinforce the results, with high certainty in these estimates.
The study shows that 70% of dispersers are from or going to Kanha, the PA with highest prey and tiger density in the study area. The results support predictions that populations with high density will participate more actively in maintaining connectivity. The dispersal depends positively on population density has been illustrated in several species.
"Our results also show that low-density populations can also have high migration rates, suggesting that tigers may disperse out of sites with low prey abundance's towards high quality habitats," says Joshi.
The study warns that unplanned development would greatly compromise landscape-level connectivity for tiger populations in Central India. The study has re-established Pench-Kanha corridor, where NHAI plans to widen the NH7. With over 13% individuals dispersing within the landscape in the last decade, any developmental activity could hamper connectivity. "For the future, there is need to identify and legally notify areas as critical wildlife corridors," said Joshi.
Central Indian landscape
Largest supporter of tigers
* The Central Indian landscape supports one of the largest tiger populations in world, and has been identified as a global tiger conservation landscape
* Due to large-scale land-use change with increasing urbanization, highways, mining in and around forested habitats, tiger populations within this landscape are isolated
* To enhance existing connectivity between tiger populations, management strategies must address tiger numbers, but more importantly landscape and habitat viability outside and between parks
* Most corridors support local people, and future conservation strategies must include plans to provide earnings to communities based on forests conserved by them