Evaluating the importance of scale in estimating tiger populations

Abstract

Population estimation is one of the most important aspects of ecological studies as it plays a pivotal role in establishing priorities for species specific conservation and for delineating management practices. The tiger serves as a flagship and umbrella species for conservation efforts in the Indian subcontinent but, unfortunately wild tiger populations are on a drastic decline owing to factors like poaching, habitat fragmentation and degradation. In such a scenario reliable population estimates prove to be of vital importance. Camera trapping technique has been widely used for population estimation of cryptic carnivores including tigers. An attempt was made, through this study, to arrive at population and density estimates for Corbett NP through camera trapping technique following the mark recapture framework and answering some key questions regarding the importance of sampling effort required for arriving at such reliable estimates. A total of 7865 trap nights yielded 358 captures of 103 individual tigers within an intensively sampled area of (MCP) 420.86 km2. The estimated density of tiger was 16.01 (±1.6) per 100 km2 for RPSV, a new approach to calculate effectively sampled area. These estimates coincided with the estimates using full MMDM method. Also, the conventional method of using half MMDM seems to overestimate the density. The estimated sampling effort required for arriving at accurate and precise estimates of the true population in terms of sampling occasions amounted to 35 - 40 days. Evaluation of the influence of trap density revealed that high trap density (25 traps/km2 ca.) is required to get reliable estimates of population irrespective of the underlying population/density gradient.