Population Status of a Cryptic Top Predator: An Island-Wide Assessment of Tigers in Sumatran Rainforests

Abstract

Large carnivores living in tropical rainforests are under immense pressure from the rapid conversion of their habitat. In response, millions of dollars are spent on conserving these species. However, the cost-effectiveness of such investments is poorly understood and this is largely because the requisite population estimates are difficult to achieve at appropriate spatial scales for these secretive species. Here, we apply a robust detection/non-detection sampling technique to produce the first reliable population metric (occupancy) for a critically endangered large carnivore; the Sumatran tiger (Panthera tigris sumatrae). From 2007–2009, seven landscapes were surveyed through 13,511 km of transects in 394 grid cells (17×17 km). Tiger sign was detected in 206 cells, producing a naive estimate of 0.52. However, after controlling for an unequal detection probability (where p = 0.13±0.017; ±S.E.), the estimated tiger occupancy was 0.72±0.048. Whilst the Sumatra-wide survey results gives cause for optimism, a significant negative correlation between occupancy and recent deforestation was found. For example, the Northern Riau landscape had an average deforestation rate of 9.8%/yr and by far the lowest occupancy (0.33±0.055). Our results highlight the key tiger areas in need of protection and have led to one area (Leuser-Ulu Masen) being upgraded as a ‘global priority’ for wild tiger conservation. However, Sumatra has one of the highest global deforestation rates and the two largest tiger landscapes identified in this study will become highly fragmented if their respective proposed roads networks are approved. Thus, it is vital that the Indonesian government tackles these threats, e.g. through improved land-use planning, if it is to succeed in meeting its ambitious National Tiger Recovery Plan targets of doubling the number of Sumatran tigers by 2022.

Coexistence between wildlife and humans at fine spatial scales

“…The estimates of tiger density across our study site in Chitwan were higher than numerous sites in Central and North India (24) and several times higher than sites in Laos, Indonesia, Malaysia, and Bhutan (25)(26)(27)(28). In addition, tiger occupancy was 12-30% greater than sites in Indonesia and India (29,30). Human foot traffic across the study site was also orders of magnitude greater than traffic reported for other areas of the tigers' range (using similar methodology) (25,26).…”

Influence of prey depletion and human disturbance on tiger occupancy in Nepal

“…More recently, tiger distribution studies outside of Nepal have used a relatively new approach (occupancy surveys) to assess tiger presence at the landscape scale (Linkie et al, 2006;Hines et al, 2010;Karanth et al, 2011;Wibisono et al, 2011;Sunarto et al, 2012). These studies differ from earlier research in Nepal, in part, by explicitly addressing the issue of detectability, accounting for search effort and analyzing additional covariates (e.g.…”

“…relative prey abundance and human disturbance). The utilization of occupancy methods across various tiger landscapes can also allow for more robust comparisons at regional scales (Wibisono et al, 2011).…”

Evaluating a Survey Landscape for Tiger Abundance in the Confluence of the Western and Eastern Ghats

“…biological pollution of wild population. Briggs and Smith 10 estimated the nitrogen and phosphorus from intensively developed shrimp ponds in Thailand as it was reported that these inputs were not converted to shrimp biomass as expected, rather there was a possibility that they were released into the surrounding environment 11,12 . It may be mentioned here that in many studies the range and severity of shrimp farming impacts have been either exaggerated or misrepresented, mainly owing to the high profitability/ visibility of the aquaculture sector, failure to distinguish between actual and hypothetical hazards 13 and projection of piece meal studies which were location-specific.…”

“…This helps in identifying source sites with high levels of certainty on tiger numbers, helping manage tiger populations in a true meta-population framework. Though attempts have been made to map occupancy of tigers at wider scales [10][11][12] , there is a need to estimate density, and absolute abundance at individual protected area scale, where reasonable logistical opportunities and resources exist. This could ultimately help in achieving global tiger recovery targets through improved coverage of scientifically assessed data.…”