Demography of a high-density tiger population and its implications for tiger recovery.
Abstract
Prioritizing conservation of source populations within landscapes is proposed as a strategy for recovering tigers globally. We studied population dynamics of tigers in Corbett National Park (CNP) in Indian Terai, which harbours the largest and highest density tiger population in any protected area of the world. Through population viability models, we demonstrate the importance of CNP in tiger recovery within western Terai. We camera trapped 521 km2 of CNP using open population capture-mark-recapture framework between 2010 and 2015 to estimate annual abundance, spatially explicit density, survival, recruitment, temporary movements, sex ratio and proportion of females breeding. We model metapopulation persistence with and without Corbett as a source within western Terai landscape at different levels of poaching and habitat connectivity. In 6 years, we recorded 6,202 photo-captures of 307 individual tigers. Annual tiger abundance and density were stable at 120 (SE 19) and 14 (SE 3) per 100 km2 respectively. Detection probability of tigers was 0.18 (SE 0.03) and detection-corrected male:female sex ratio was female biased (0.80 SE 0.13). Apparent annual survival probability was 0.79 (SE 0.05) for females and 0.60 (SE 0.04) for males. Survival of tigers in CNP (0.68 SE 0.12) was lower than that reported for other populations. CNP tigers showed high reproduction with 54.8 (SE 5.1)% females breeding and with addition of 35 (SE 8)% as new recruits to the population each year. Small tiger populations in western Terai with moderate poaching could only persist through dispersal from CNP. Synthesis and applications: Corbett tiger population was characterized by a stable high density, high reproductive rate and low survival, resulting in high turnover rates (32%-48%) between successive years. Such source populations could sustain low-level poaching and with habitat connectivity, recover tiger populations across the landscape. This study establishes potential thresholds that can likely be achieved by tiger populations under optimal natural conditions and highlights the importance of prioritizing conservation of source populations within tiger landscapes. This information can be used to plan and implement realistic tiger recovery programmes globally.